Application guide. The LEDset interface. www.osram.com/ledset

Application guide. The LEDset interface. www.osram.com/ledset
www.osram.com/ledset
Application guide.
The LEDset interface.
CONTENTS
General notes:
As the specifications of the applied components are subject to change, OSRAM does not take
liability for the technical accuracy of the application solutions shown in this application guide.
For current specifications, please refer to the data sheets of the respective components.
Please also note that LED standards are changing rapidly and that this application guide can
therefore only reflect the status of the listed standards on the date published. Please check the
latest edition of any standard at the following websites or with your national trade association.
www.cenelec.org
www.cen.eu
www.iec.ch
2
CONTENTS
1. Introduction
1.1. Features and benefits
4
5
2. LEDset specifications
2.1. General overview
2.2. LEDset characteristic
2.2.1. General description
2.2.2. Implementation in the OSRAM ECG
2.3. Technical details
2.3.1. Bias current (Iset)
2.3.2. +12Vset
2.3.3. Fault protection
2.3.4. Insulation
2.3.5. Color coding
2.3.6. Cable length
2.3.7. Fault conditions/troubleshooting
2.3.7.1. Incorrect wiring
2.3.7.2. Missing control wire (Vset)
2.3.8. Connection of multiple ECGs
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3. LEDset applications
3.1. Current setting
3.1.1. Setting by external resistor
3.1.2. Step dimming (StepDIM)
3.2. Local dimming
3.2.1. Potentiometer application
3.2.2. Light sensor application
3.2.2.1. Using OSRAM DIM
MICO/PICO
3.2.2.2. Using customized sensors
3.2.2.3. General notes on local
dimming: LEDset, “current set”
combination
3.3. Thermal derating
3.3.1. Overtemperature protection
3.3.1.1. Application solution 1 –
TMP300 solution
3.3.1.2. Application solution 2 –
LM26 solution
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24
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3.3.1.3. Application solution 3 –
NPC SM6611 solution
3.3.1.4. Application solution 4 –
SI S-5841 solution
3.3.1.5. Application solution 5 –
MM3488 solution
3.3.1.6. Application solution 6 –
TC620(1) solution
3.3.1.7. General notes on IC
temperature switches:
choice and usage
3.3.2. Overtemperature protection
(discrete NTC)
3.3.2.1. Application solution 1 –
overtemperature protection
by comparator
3.3.2.2. Application solution 2 –
overtemperature management
by comparator:
two-step output
3.3.2.3. Application solution 3 –
overtemperature management:
continuous derating
and switch-off
3.3.2.4. Application solution 4 –
LEDset and current set
combination: direct NTC
connection
3.3.2.5. Application solution 5 –
overtemperature management:
microcontroller
(MCU) approach
3.4. +12Vset auxiliary supply
3.4.1. Aesthetic use
3.4.2. Active cooling
3.5. Constant lumen output
3.6. Combination of features
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INTRODUCTION
1. Introduction
LED technology is changing the world of general lighting. In
luminaire design, however, the various benefits of LEDs, e.g.
their high level of flexibility in operating luminaires, can only
be achieved with perfectly matched control gears. This is further complicated by the rapid improvement of the efficacy
and current capability of LED technologies, which asks for
even greater adaptability of the corresponding control gears.
Purpose of this application guide:
The purpose of this application guide is to provide basic technical information on the LEDset interface, focusing on application
solutions that illustrate the specific functions of this new interface and show how these can be used. The application solutions
demonstrate that the LEDset interface opens up many opportunities for customizing your LED-based luminaire: the simplicity
and flexibility of LEDset gives you the freedom to develop new
luminaire system features.
4
OPTOTRONIC® control gears with LEDset interface can meet
this demand for greater adaptability by supporting a wide
power and current range and by their future-proof design,
which makes them ready for coming LED generations.
INTRODUCTION
1.1. Features and benefits
LEDset helps you to meet important market requirements:
•
•
•
•
Future-proof solutions in terms of lumen output
Long-life operation
Customization of the luminaire
Energy saving
OPTOTRONIC®
In combination with OSRAM LED power supplies, the
LEDset interface offers full flexibility and a future-proof
system with the following features and benefits:
•
•
•
•
•
•
Current setting
Thermal protection
High current accuracy
Auxiliary supply 12 V
Local dimming
Simple wiring
LED module
+12Vset
Signal (Vset)
GNDset
Power lines
Current
setting
Local
dimming
• By resistor
• With lin/log
potentiometer
• StepDIM
Overtemperature
derating
Auxiliary
supply
Constant
lumen output
• For control
logic (μc, IC)
on the LED
module
• For 12 V lowpower LED
module
Figure 1: LEDset application features.
5
LEDset SPECIFICATIONS
2. LEDset specifications
2.1. General overview
LEDset is a 3-wire analog control interface designed for
OPTOTRONIC® constant-current LED power supplies. It
allows setting the output current of the electronic control
gear (ECG) by providing a highly accurate voltage reference
(Vset) to the ECG. Thanks to the control accuracy and simplicity of LEDset, control gears become highly adaptable and
can cover a wide range of applications. The output current
can be set/dimmed by a passive device (e.g. resistor) or by
an external imposed-voltage control signal.
Moreover, the interface gives more freedom in the design of
customized systems by providing a stabilized 12 V auxiliary
voltage (+12Vset) that can supply an active circuit, for example on the LED module, extending a simple temperaturedependent current derating circuit to a more complex microcontroller-based flux control.
Figure 2: LEDset interface wiring (block diagram).
6
The main features of the LEDset interface can be
summarized as follows:
• Output current setting interface for constant-current ECGs
• 3-wire interface
– +12Vset: Stabilized 12 V auxiliary voltage (+/-10 %)
– Vset: Voltage reference in the range of 0 to 12 V (+10 %)
– GNDset: Ground reference of the LEDset interface
• Output current setting by analog input voltage control (Vset)
– For current setting, the Vset control voltage is within the
range of 10 V
– The LEDset characteristic is a fixed relationship between
the Vset voltage and the percentage of the maximum
nominal current of the control gear (relative coding)
• High-output LED current accuracy
– Overall control system provides an Inommax tolerance
of up to +/-5 %
– Accurate bias current generator on Vset for very precise
current setting via passive control (fixed/variable resistor)
• 12 V auxiliary output (+12Vset) for the supply of electronic
ICs/circuits or the control of a fan (future extension)
• ECGs can be used in a wide power and current operating
range
LEDset SPECIFICATIONS
2.2. LEDset characteristic
2.2.1. General description
With the LEDset interface, the output current can be defined
relative to the maximum nominal output current of the control
gear.
The basic relationship between the LEDset voltage (Vset)
and the ECG output current (Iout) is defined by the following
equation:
Iout
Inommax
(Vset 1)
where Inommax is the maximum nominal output current of
the ECG and Vset voltage is the voltage between Vset and
GNDset.
The relationship is valid for values of Iout that are within
the current range of the control gear, i.e. between Imin
and Inommax.
The generic Iout versus the Vset characteristic is shown in
figure 3.
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Figure 3: Generic Iout vs. Vset characteristic.
Designation of lines:
Blue line: Ideal case
Orange line: Typical real ECG behavior with Imin
limitation and no turn-off capability
0 < Vset < Vmin
Iout = lmin or lout = 0 (see chapter 2.2.2. for details)
Vmin < Vset < 10 V
Iout according to LEDset relationship
10 V < Vset < 11 V
Iout = Inommax
11 V < Vset < 12 V + 10 % (Vset, open)
Iout = Imin (i.e. Iout = 0 if the ECG has a turn-off capability)
Table 1: LED output current as function of Vset.
7
LEDset SPECIFICATIONS
Note:
Vmin is the Vset voltage value corresponding to the minimum
deliverable current (Imin) of the ECG. The Imin is specified in
the datasheet of the applied ECG. Based on the LEDset relationship between Iout and Vset, it is possible to calculate the
typical Vmin of the ECG.
2.2.2. Implementation in the OSRAM ECG
Based on the general LEDset specification, two different
LEDset implementations can currently be found in constantcurrent OSRAM ECGs (for details, please refer to the datasheet of the specific product).
Figure 4a: Case I.
Product examples:
3DIM + LEDset (LT)
OT 45/220-240/700 3DIMLT E
OT 90/220-240/700 3DIMLT E
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Example:
When using the OT 35/220-240/700 with a nominal current
of 700 mA, the minimum current is 100 mA (according to the
datasheet of the ECG) and the Vmin is as follows:
Vmin
Imin
Inom
9+1
2.28 V
Basically, the two cases differ due to the minimum current
limitation of the ECGs. An ECG’s turn-off capability – rather
than the minimum current holding between Vmin and 0 V –
makes the difference between the cases.
The following diagrams describe the different cases implemented in OSRAM LEDset ECGs:
Figure 4b: Case II.
LEDset
OT 90/220-240/700 LT E
Vmin
Product examples:
LEDset (LT) + current setting (CS)
OT 35/220-240/700 LTCS
OT 45/220-240/700 LTCS
LEDset SPECIFICATIONS
2.3. Technical details
This chapter gives a general overview of the technical details
of the LEDset interface. For further details and deviations
from this basic information, please refer to the datasheet
and instruction sheet of the respective control gear.
2.3.1. Bias current (Iset)
2.3.4. Insulation
The LEDset interface is an active interface since the Vset input can actually generate a constant current output (bias
current), allowing the Vset voltage to be achieved through
“passive” circuits (e.g. current setting by resistor, light sensors etc.).
All ECGs with LEDset interface have the following minimal
insulation barriers:
The integrated current generator provides a very stable bias
current (Iset) of 274 μA over the complete operating range of
the control gear. Thanks to this feature, unwanted current
variations due to temperature changes, which occur in many
ECGs with similar control interfaces, can be avoided.
2.3.2. +12Vset
The stabilized 12 V auxiliary voltage is able to supply a
current of up to 15 mA (laux). The voltage accuracy is within
a tolerance of ±10 %. A future power extension will provide
an even greater capability to supply more powerful loads
(such as an external fan for active cooling applications).
For details regarding the maximum allowable output power,
please refer to the datasheet and instruction sheet of the
respective control gear.
2.3.3. Fault protection
The +12Vset is protected against short circuit (+12Vset –
GNDset). Vset is protected up to the 12 V + 10 %.
Primary
circuit
Secondary
circuit
LEDset
Primary
circuit
–
Depending
on the ECG
Depending
on the ECG
Secondary
circuit
Depending
on the ECG
–
No insulation
LEDset
Depending
on the ECG
No insulation
–
Table 2: Insulation barriers of LEDset ECGs.
There is no galvanic insulation between the LEDset interface
and the secondary circuit.
Note: If the LEDset ECG is to be used in a system that must
be classified as SELV (Safety Extra-Low Voltage), any circuit
connected to the LEDset interface of an SELV or SELVequivalent control gear can only be used if double-insulated
from the mains.
The LEDset interface has no specific protection against electrostatic discharge (ESD). Therefore, it is recommended that
any circuit (e.g. accessible potentiometer) connected to the
LEDset interface port has a proper insulation against touchable parts.
Moreover, the negative pole of the LED load (LED-) must not
be connected to the GNDset terminal.
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LEDset SPECIFICATIONS
2.3.5. Color coding
2.3.6. Cable length
The color coding for the connector of the LEDset interface is
defined as follows:
The maximum length of LEDset cables should not exceed
2 m. Further limitations to cable length generally derive from
EMI emission or immunity issues or directly from product
specification details. For detailed information, please refer to
the datasheet or instruction sheet of the respective LEDset
control gear.
LED+
Red
LED-
Black
LEDset GNDset
Gray
LEDset Vset
Violet
LEDset +12Vset
Blue
Table 3: Color coding.
LED+ and LED- are the power outputs of the control gear.
The position and order of the terminals can vary between the
different LEDset ECG types.
2.3.7. Fault conditions/troubleshooting
2.3.7.1. Incorrect wiring
2.3.7.2. Missing control wire (Vset)
The LEDset interface has been designed to inherently protect itself and the LED module against incorrect wiring on the
secondary side of the control gear. Incorrect connections
between LED+ and Vset or GNDset can irreversibly damage
the ECG.
LEDset is an interface intended for the current setting and
thermal management of an LED module. If the Vset terminal
is not connected to the control unit, the thermal protection of
the LED module and its correct current setting will not work.
Other possible incorrect wirings on the secondary side do
not affect the operation of the ECG once they are removed
(irrespective of problems regarding the connected external
LEDset ECGs).
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This fault condition may result in an undetected overheating
of the LED module. In order to protect the LED module in
this condition, the absence of a control signal (Vset open or
Vset * 11 V) is detected and the ECG is shut down or set to
its minimum current (see figure 3).
LEDset SPECIFICATIONS
2.3.8. Connection of multiple ECGs
Depending on the LEDset control gear, the Vset signals can
be connected in parallel to set the current of multiple ECGs
by a resistor. This connection is allowed in case of a local
dimming application on a luminaire supplied by more than
one ECG.
In general, if n is the number of ECGs to be connected together to a local dimmer or current setting resistance, Rset/n
is the resistance value to be considered (where Rset is the
value needed to set the current of one single ECG).
Example: an office luminaire with two ECGs locally dimmed
by a 22 k1 potentiometer.
Figure 5 shows a parallel connection of two LEDset interfaces. The interfaces share a resistor Rset, with which it is
possible to set the output current. Current setting by external
resistor is explained in detail in chapter 3.1.1.
Figure 5: Parallel connection of two LEDset interfaces.
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LEDset APPLICATIONS
3. LEDset applications
3.1. Current setting
3.1.1. Setting by external resistor
If the application requires a specific fixed output current, the
easiest way to set the output current is to apply a resistor
between Vset and GNDset.
As mentioned in chapter 2.3.1., the LEDset interface is an
active interface that is able to generate a constant current
output (Iset) and thus allows the use of “passive” circuits
(e.g. resistor) to achieve the setting voltage (Vset).
Figure 6: Current setting by external resistor.
The resistor can be placed either on the terminal block of the
ECG or on the LED module (plug-and-play solution but with
two additional wires that have to be considered for cabling
design).
As a function of the LEDset interface, the Vset value is
related to the percentage of the ECG’s maximum nominal
current.
Iout
[ %]
Inommax
12
(Vset 1)
9
100
This means that the absolute value of the output current
depends on the maximum nominal current of the ECG.
Setting the output current Ioutmax on an ECG with Inommax =
700 mA will differ from setting the same Iout on an ECG with
Inommax = 1500 mA.
LEDset APPLICATIONS
The following table shows the output current values obtained by applying
a 1 % resistor (from E96 series unless otherwise specified) for two different
ECGs with a nominal current of 700 mA and 1500 mA, respectively.
Rset – E96 series
(unless otherwise
specified)
Vset [V]
Iout/Inom [%]
Inom [mA] = 700
Inom [mA] = 1500
0
0.0
0
0
0
3830
1.0
1
4
8
7500
2.1
12
82
176
11300
3.1
23
163
349
14700
4.0
34
235
505
15000
4.1
35
242
518
19100
5.2
47
329
706
20000 (E24)
5.5
50
348
747
21000
5.8
53
370
792
23200
6.4
60
417
893
25500
7.0
67
466
998
27000 (E24)
7.4
71
498
1066
28000
7.7
74
519
1112
30100
8.2
81
564
1208
34000
9.3
92
647
1386
36500 (E48)
10.0
100
700
1500
38300
> 10.0
100
700
1500
39000 (E24)
> 10.0
100
700
1500
40200 (and up to 60000) > 10.0
100
700
1500
Table 4: Current setting by external resistor.
For more information, please see the notes on page 14.
13
LEDset APPLICATIONS
Note 1: The E96 series covers a wide range of values. The
table contains only some sample values of this series. Please
check the standard E96 series to find the value best suited
for meeting your current setting requirements.
Note 4: Since the Iset current value is very low, the power
rating of the resistor is not an issue to be considered when
selecting the resistor (considering a maximum value of
50 k1
PRset = 3.8 mW).
Note 2: The values given above are calculated without considering the possible power and/or output voltage and/or
minimum output current limitations which depend specifically
on the output characteristics of the chosen ECG. Please
refer to the respective product datasheet.
Note 5: If the value of the commercial resistor differs too
much from the calculated resistance, connecting resistors in
series/parallel might help to obtain the precise required value.
Note 3: The resistor tolerance has an effect on the accuracy
of the current setting. Available standard tolerances are 5 %,
2 %, 1 %, 0.5 %, 0.25 % and 0.1 %. LEDset ECGs are designed to provide up to 5 % of the overall control accuracy
(Rset – Iout) if Rset is a resistor with a tolerance of up to 1 %.
If higher than 1 %, the tolerance of Rset must be considered in
the Iout tolerance calculation.
Note 6: It is not recommended to set the Vset by dividing
the +12Vset voltage by a resistor divider. This setting is in
fact more complicated. Moreover, the stated accuracy tolerance of ±5 % for the overall control system may not be longer achieved because it is directly affected by the +12Vset
voltage tolerance which is ±10 %.
Example:
This example is meant to help in choosing the most suitable commercial resistor for a given system.
The calculation applies to an OT 35/220-240/700 LTCS in LEDset configuration to set an output current of 580 mA.
Starting from the basic relationship:
Vset
1+9
Iout
Inom
8.33 V
where Iout = 580 mA and Inommax = 700 mA
Therefore:
Rset
Vset
Iset
30.87 kȍ
where Iset = 274 μA
Looking at available values of commercial resistors (i.e. E96 series), 30.9 k1 is the best choice.
The recalculated real current setting would be:
Vset
14
Rset Iset
8.47 V
and therefore Iout = 580.7 mA
LEDset APPLICATIONS
3.1.2. Step dimming (StepDIM)
Based on the previous chapter (3.1.1.), the current setting
by resistor can be easily extended by an additional step dimming function. By switching between two external resistance
values, the output current can be changed to two different
levels (i.e. one to set the nominal current to 100 % and one
to step down to 40 %). Shorting the Vset to GNDset allows
turning off the LED module while the ECG is still supplied
with mains voltage.
Possible solutions are shown in the following block diagram:
7a: Manual solution.
7b: Relay-based solution.
Figure 7: Step dimming by two resistor values.
For more information, please see the note on page 16.
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LEDset APPLICATIONS
Switching can be carried out either by a switch (manual
activation, see figure 7a) or by using a relay (see figure 7b).
While Rset1 sets the current level Iout1, the equivalent parallel
resistance RsetEQ (Rset1||Rset2) sets Iout2.
Note: In both cases (7a and 7b), two main issues need
to be considered when selecting the components:
• Performance
The relay contacts or switch contacts must be suitable for
applications with a very low current. Selecting the right
type (low contact resistance, oxidation-proof etc.), i.e.
golden-plated or bifurcated contacts, is therefore essential.
• Safety/SELV (Separated or Safety Extra-Low Voltage)
In case of SELV systems, insulation between contact circuit and actuator part – the human finger (7a) or the coil
of the relay (7b) – must be considered. For example, if
the relay control line is in some way referred to the mains
potential, a double insulation must be provided between
the coil circuit and the contact side of the component so
that the SELV property of the system is ensured. In case
of a control line that is already double-insulated from the
mains, a standard low-cost signal relay can be used.
In any case, please refer to the safety standard EN
61347-2-13 for ECG requirements and to EN 60589-1
for luminaire requirements.
For a relay-based solution (see figure 7b) where the control
line is not galvanically insulated from the mains or the mains
potential, the following relays can, for example, be used:
Control line
Supplier
230 VAC
Low voltage
OMRON
G2R1Z230VAC
G2R1AP3230VAC
G5V1 series (one contact pole)
G6S series (golden-plated – 3 V, 5 V, 12 V, 24 V)
PANASONIC
PA(D)1a series (bifurcated – 3 V, 5 V, 12 V, 24 V)
Table 5: Step dimming by resistor – suitable relays.
The use of double-contact or/and bi-stable relays extend
the configuration possibilities of the LEDset interface
(more current steps, pulse-based relay control line etc.).
16
LEDset APPLICATIONS
3.2. Local dimming
3.2.1. Potentiometer application
If an application requires the dimmability of a luminaire, a simple and economical solution can be to implement a local dimming function by a logarithmic or linear potentiometer. In this
case, the term “local dimming” refers to the possibility to set
the current of a single luminaire system by a potentiometer.
Figure 8: Local dimming – potentiometer application.
The LEDset interface has been designed for the application
of standard potentiometers with standard rated resistances
of 47 k1 or 50 k1 and a tolerance of ±20 %.
> 11 V, changing the output current setting to Imin or 0 %
(see table 1).
Using a potentiometer with a nominal value within this range
allows dimming by changing the current from Inommax
(at Vset > 10 V but less than 11 V) to 0 mA (at Vset < 1 V) or
higher, taking account of the Imin limit and the turn-off
capability (see cases I and II in chapter 2.2.2.).
Note 2: Local dimming means that the used dimming device
is a single-insulated potentiometer or a potentiometer that
is part of a multifunctional device and needs to be doubleinsulated from the parts related to the mains potential if the
application is SELV-classified (see general note on insulation
in chapter 2.3.4).
Note 1: Potentiometers with nominal values lower than
47 k1 - 20 % do not provide the complete dimmable range of
the output current. Nominal values higher than 50 k1 + 20 %,
however, can enable the device to reach the range of Vset
Suitable potentiometers for this application are for example:
• Vishay P16 NP 47K 20 % A (linear potentiometer)
• Vishay P10 YM AG 47K 5 % (medium-cost potentiometer)
• Tyco CB10KH473ME (low-cost potentiometer)
17
LEDset APPLICATIONS
3.2.2. Light sensor application
Daylight compensation can be easily obtained with the
LEDset interface by connecting existing commercial light
sensors (only plug-and-play sensors as described in the
following chapter). Light sensing can be approached by
using standard 1…10 V-compatible light sensors or by developing light sensors from IC chips and converting their output
signal to the Vset range of the LEDset interface.
3.2.2.1. Using OSRAM DIM MICO/PICO
DIM MICO/PICO is a light sensor from OSRAM which is
compatible with 1…10 V interfaces. The sensor works once
it is connected directly between Vset and GNDset.
This sensor is used to monitor, measure and maintain the
brightness level of its detection area to a preset value, which
is adjustable by a setpoint potentiometer screw. Once the
daylight decreases and the brightness of the area reaches or
falls below the preset value, the sensor starts to increase its
impedance between Vset and GNDset, thus increasing the
Vset voltage level. The higher current demand to the LEDset
ECG results in an artificial light compensation by the light of
the LED module.
Note: The 274 μA of Iset are enough to supply the sensor.
Particular attention should be paid to presetting the brightness setpoint of the sensor, referring to the setup procedures
described in the DIM MICO/PICO datasheet. In any case,
Vset should be in the range of 10 to 11 V at the desired
maximum current output (no daylight present) to avoid
reaching the turn-off range of the LEDset interface characteristic (see figure 4).
This warning does not apply if a LEDset ECG is used in
combination with a current set (CS) configuration. For more
details, please see chapter 3.2.2.3. General notes on local
dimming: LEDset and “current set” combination.
For more detailed information about DIM MICO/PICO,
please refer to www.osram.com/lms-sensors
18
Figure 9: Local dimming – light sensor application with DIM MICO/PICO.
LEDset APPLICATIONS
3.2.2.2. Using customized sensors
Various light sensors can be used in place of the previously
mentioned OSRAM DIM MICO/PICO. Once the output
sensor is compatible with the LEDset interface, the resulting
control possibilities can perfectly fit the needs of the application.
In the following example, a light sensor is connected to a
microcontroller (MCU) before going to the Vset output signal,
introducing more flexibility into the light management and,
at the same time, adding more managing possibilities (i.e.
temperature management as explained in chapter 3.3.2.5.
Application solution 5 – overtemperature management:
microcontroller (MCU) approach).
Please consider: When using a LEDset interface, the Vset
voltage range needs to be considered. Regardless of the used
sensor, the maximum Vset voltage should not exceed 11 V
(as described in chapter 2.2.1. General description) because,
otherwise, Imin or the turn-off condition (Iout = 0 mA) could
be reached.
For some ECGs, it is possible to exceed the 11 V in a specific
operation mode, while keeping the nominal output current
(Inommax) at its maximum value. This behavior is described in
the next chapter (3.2.2.3.).
Figure 10: Local dimming – light sensor – custom application.
19
LEDset APPLICATIONS
3.2.2.3. General notes on local dimming:
LEDset, “current set” combination
For some applications, the turn-off capability provided by
the LEDset characteristic above 11 V might not be an
appropriate feature.
Therefore, some LEDset ECGs can combine the LEDset
interface with the so-called “current set” (CS) feature.
Product examples are the OT 35/220-240/700 LTCS and
OT 45/220-240/700 LTCS (LTCS means “LEDset” (LT)
and “current set” (CS)).
20
On those devices, it is possible to set the current control
functionality by dip switch to work with a “pure” LEDset
interface as described in chapter 2, or to combine it with a
current set (CS) configuration: 350, 500 and 700 mA where
the maximum nominal currents (Inommax) can be selected.
The Vset signal can still be used to control/set the output
current of the ECG as in a “pure” LEDset control –
with the difference being only in regards to the Vset characteristic above 11 V.
A typical characteristic of this configuration is shown in
figure 11.
LEDset APPLICATIONS
Figure 11: Local dimming – example of the LTCS characteristic of the OT 35(45)/220-240/700 LTCS.
Above 10 V and higher, the output current is maintained at
its maximum nominal value without turning off the ECG. In
this case, the accuracy features of the LEDset interface
can also be combined with inflexible light sensors with an
output range higher than 11 V. This capability to maintain
the Inommax from 10 to +12 V +10 % without turning off the
ECG output easily solves possible issues.
Furthermore, the current set configuration also allows the
ECG to continuously supply its Inommax current if the Vset
input is left open (floating).
21
LEDset APPLICATIONS
3.3. Thermal derating
With its simple and flexible properties, the LEDset interface
allows users to manage the LED module temperature directly
with the ECG.
Luminaire manufacturers prefer to customize their products
via different approaches to manage temperature deratings
and/or protections.
One-step (switch-off) or two-step (intermediate current level
and switch-off) solutions satisfy the simpler, more common
requirements for thermal protection/management (figures
12a and 12b). Besides, more sophisticated management solutions need to control a continuous derating of the current
as a function of the temperature before turning off the LED
module (figures 12c and 12d).
Moreover, a different luminaire type, luminaire application or
a general luminaire maker approach always requires a specific
Iout vs. Tset (LED module temperature) characteristic in
terms of temperature thresholds and current values.
22
The LEDset interface allows users to strategically define their
module temperature management, thus providing the possibility to implement their own specific solution with
reliable accuracy.
Thanks to the auxiliary voltage output of the ECG (+12Vset),
simple and more sophisticated “active” solutions can be
realized and directly implemented on the LED module or on
a smart spot of the luminaire.
Providing an extremely high level of flexibility and overall
accuracy, the LEDset interface is also suitable for emergency
applications where the fine-tuning is essential to ensure
safe and reliable operation at an ambient temperature of
up to 70 °C.
LEDset APPLICATIONS
Application solutions
Complexity
level
For detailed information,
please see chapters:
a)
Low
3.3.1. Overtemperature protection
3.3.1.1. Application solution 1 – TMP300 solution
3.3.1.2. Application solution 2 – LM26 solution
3.3.1.3. Application solution 3 – NPC SM6611 solution
3.3.1.4. Application solution 4 – SI S-5841 solution
3.3.1.5. Application solution 5 – MM3488 solution
Medium
3.3.2. Overtemperature protection (discrete NTC)
3.3.2.1. Application solution 1 – overtemperature protection by comparator
Low
3.3.1. Overtemperature protection
3.3.1.6. Application solution 6 – TC620(1) solution
Medium
3.3.2. Overtemperature protection (discrete NTC)
3.3.2.2. Application solution 2 – overtemperature management
by comparator – two-step output
c)
Medium
3.3.2. Overtemperature protection (discrete NTC)
3.3.2.3. Application solution 3 – overtemperature management:
continuous derating and switch-off
d)
Very low
3.3.2. Overtemperature protection (discrete NTC)
3.3.2.4. Application solution 4 – LEDset and current set
combination: direct NTC connetion
e)
Medium/
high
3.3.2. Overtemperature protection (discrete NTC)
3.3.2.5. Application solution 5 – overtemperature management:
microcontroller (MCU) approach
b)
Figure 12: Thermal derating – overview of application solutions.
23
LEDset APPLICATIONS
3.3.1. Overtemperature protection
A possible approach for overtemperature protection is to
simply use the so-called “temperature switch ICs” – an easy,
relatively cheap and low-component-number solution.
3.3.1.1. Application solution 1 – TMP300 solution
TMP300 (Texas Instruments) is a digital output temperature
switch IC. Its voltage supply range is 1.8–18 V, therefore it
can be directly supplied by the LEDset +12Vset terminal.
The open drain output is to be connected to the Vset terminal of the LEDset interface, thus obtaining the ECG shut-
Figure 13: Thermal protection – TMP300 solution.
For more information, please see the general notes on page 33.
24
The following chapters provide some example solutions of
different simple implementations realized by commercially
available ICs with integrated temperature sensing capability. A
schematic reference shows their interface with LEDset ECGs.
down when the temperature of the LED module exceeds a
certain TsetTH (temperature threshold).
The trigger temperature TsetTH can be set between -40 °C
and +125 °C by an external resistor (Rtemp), calculated as
follows:
Rtemp
10 (50 + TsetTH)
[kȍ]
3
LEDset APPLICATIONS
The schematic of the circuit is shown in figure 13. Proper
by-pass capacitors (100 nF 25V X7R SMD type) should be
added on the supply line and Rtemp to ensure a noiseless
application.
The hysteresis of the temperature threshold can be set in
two different ways:
• 5 °C if pin 4 is grounded;
• 10 °C if pin 4 is connected to pin 6 (Vcc).
A setting resistance (Rset) can be integrated into the
circuit in order to set the operating current of the system
as described in 3.1.1.
Example:
Conditions:
Iout = Inommax
TsetTH = 80 °C
Rtemp
10 (50 + TsetTH)
3
433 kȍ
Form E96 series, a commercial value is 432 k1 ± 1 %.
Figure 14: TMP300 solution – output characteristic.
Based on this value, the
TsetTH
3 Rtemp
10
2
50
79.6 °C
1
For Rset, a 39 k1 ± 1 % will provide that Iout = 100 %
Inommax. Connecting pin 4 to the GNDset enables a hysteresis
of 5 °C. Figure 14 shows the resulting behavior of this circuit.
Figure 15: TMP300 solution – real circuit (1) appearance with connector
block (2).
25
LEDset APPLICATIONS
3.3.1.2. Application solution 2 – LM26 solution
LM26 (National Semiconductor) is a digital output temperature switch IC with a factory-programmed trip point ranging
from -55 °C to 110 °C (in increments of 1 °C). LM26 can have
four different configurations of the digital output. Version C
(active-high, push-pull on OS output) is needed for this application.
Figure 16: Thermal protection – LM26 solution.
In figure 16, a reference schematic is shown. Since the maximum operating voltage is limited to 5.5 V, a voltage regulator
is needed in order to supply LM26 from the LEDset interface.
The simplest solution is to clamp the supply voltage on pin 4
with a Zener diode (D1). In order to ensure a sufficient reverse
current to the diode, a proper value of R1 has to be selected.
A by-pass capacitor (C1) between pin 4 and ground (pin 2) is
recommended.
Figure 17: LM26 solution – output characteristic.
2
The hysteresis of the temperature threshold can be set at:
• 10 °C if pin 1 is grounded;
• 2 °C if pin 1 is connected to pin 4 (Vcc).
1
The LM26 digital output drives a transistor (Q1) which pulls
the Vset node down when an overtemperature condition is
detected. Q1 can either be a bipolar or a logic-level FET device with a voltage rating above 12 V. A device with low leakage current (namely lower than 1 μA) is mandatory. For this
reason, bipolar transistors are preferred (i.e. BC847).
For more information, please see the general notes on page 33.
26
Figure 18: LM26 solution – real circuit (1) appearance with connector
block (2).
LEDset APPLICATIONS
3.3.1.3. Application solution 3 – NPC SM6611 solution
SM6611 (NCP) is a temperature switch IC able to change
the state of an output pin (invert) when the chip temperature
exceeds a preset temperature (TsetTH). The TsetTH temperature detection is managed by hysteresis (10 °C) to prevent
unstable output switching (sensed temperature close to the
preset temperature). SM6611 series propose 6 preset TsetTH
temperatures, 2 output configurations (push-pull, open drain).
In figure 19a, a reference schematic is shown. The maximum
operating voltage of the IC is +15 V and the open drain
output can withstand 10 V maximum. The control could be
directly used as in figure 19a. A safer implementation is
shown in figure 19b where the output pin is connected to
the Vset via transistor (in case of a voltage higher than 10 V).
A maximum leakage current of 1 μA on the open drain
output allows the use of the IC without affecting the control
accuracy (over the Iset).
Figure 19a: Thermal protection – SM6611 solution.
Figure 19b: Thermal protection – SM6611 solution.
Example:
Considering a TsetTH of 75 °C, the following devices can
be used:
• SM6611DAH in case of direct connection to LEDset
(case a – not recommended)
• SM6611DBH in case of direct connection to LEDset via
transistor (case b)
For more information, please see the general notes on page 33.
27
LEDset APPLICATIONS
3.3.1.4. Application solution 4 – SI S-5841 solution
The SI S-5841 (SI – Seiko Instruments Inc.) series is a temperature switch IC which detects a certain temperature and
sends a signal to an external device. Various combinations
of the parameters such as the detection temperature, output
form and output logic can be selected.
In package SOT-23-5, five TsetTH temperatures are available
as factory settings (+55 °C, +65 °C, +75 °C, +85 °C, +95 °C).
the detection temperature (+TD), the DET pin is at a low level.
Although the output from the comparator goes active due to
noise if the period in which this status continues is shorter
than the noise suppression time, the DET pin keeps its low
level. However, if the period in which the output of the internal comparator is active is longer than the noise suppression
time, the DET pin is set to a high level. In case of +12 V
range supply voltage, the noise suppression time is about
1.2 –1.5 s.
More than the previous ICs, the S-5841 series also has a
noise suppression time (tdelay). If the temperature is lower than
In figure 20a, a reference schematic is shown. The maximum
operating voltage of the IC is +12 V and the open drain
output can withstand 12 V maximum. The control could be
directly used as in figure 20a. By the way, a safer and highly
recommended implementation is shown in figure 20b where
the output pin is connected to the Vset via a transistor and
the supply voltage is simply reduced by a Zener diode and a
resistor (+12 V can have a tolerance of +10 %).
Figure 20a: Thermal protection – S-5841 solution (direct connection).
Figure 20b: Thermal protection – S-5841 solution (via output transistor and voltage regulator).
A maximum leakage current of 1 μA on the open drain output
allows the use of the IC without affecting the control accuracy
(over the Iset).
Example:
Considering a TsetTH of 75 °C and a hysteresis of 4 °C,
the following devices can be used:
• S-5841B75D-M5T1U (open drain) in case of direct
connection to LEDset (case a – not recommended)
• S-5841B75A-M5T1U (CMOS out) in case of connection
to LEDset via transistor (case b)
In both cases, pin 1 must be tied to Vcc (pin 4).
The temperature hysteresis is set by the HYS1 pin (and/or
HYS2 pin), offering the choice between four values: 0 °C,
2 °C, 4 °C, 10 °C (the configuration depends on ordering part
number and package type).
For more information, please see the general notes on page 33.
28
LEDset APPLICATIONS
3.3.1.5. Application solution 5 – MM3488 solution
The MM3488 (MITSuMI) is a temperature switch IC that
changes the IC output level from “low” to “high” when the
temperature around the IC reaches the detection temperature. With the hysteresis function (5 °C, 10 °C, 15 °C), the IC
output level returns to “low” when the ambient temperature
drops to the temperature hysteresis selected after detection.
Detection temperature TsetTH can be selected in steps of
1.0 °C between 60 and 90 °C with rank expansion (available
as factory-trimmed value), with a detection temperature
accuracy of ±2.0 °C.
The very-small-outline package SSON-4B allows saving
space on the LED module, compensating for the higher
overall number of components with respect to the previous
solutions.
A noise rejection time tnoise between 250 and 500 μs allows
debouncing the temperature signal, preventing unstable output switching caused by possible noise.
In figure 21, a reference schematic is shown. Since the maximum operating voltage is limited to 5.5 V, a voltage regulator
is needed in order to supply the MM3488 via the LEDset
interface. The simplest solution is to clamp the supply voltage with a Zener diode (D1). In order to ensure a sufficient
reverse current to the diode, a proper value of R1 has to be
selected. A by-pass capacitor (C1) between pin 4 and ground
(pin 2) is recommended.
D1 = 5 V1 5 % signal Zener diode (i.e. NXP BZT52H-C5V1)
C1 = 100 nF 25 V 10 % X7R 0603
Q1 = NPN signal transistor (BC847)
R1 = 1K 5 % 0603
R2 = 10K 5 % 0603
R3 = 100K 5 % 0603
Figure 21: Thermal protection – MM3488 solution (via output transistor).
Since the IC output is only an open drain, a pull-up resistor
is needed.
Example:
Considering a TsetTH of 75 °C and a hysteresis of 5 °C,
the following device can be used:
• MM3488575RRE
For more information, please see the general notes on page 33.
29
LEDset APPLICATIONS
The TC620 and TC621 (from Microchip) are programmable
logic output temperature detectors designed for use in thermal management applications. The TC620 features an onboard temperature sensor, while the TC621 connects to an
external NTC thermistor for remote sensing applications.
the user-programmed limits. The CONTROL (hysteresis)
output is driven high when the temperature equals the “high
limit” setting and returns to “low” when the temperature falls
below the “low limit” setting. This output can be used to provide “on/off” control to a cooling fan or heater. The TC621
provides the same output functions, except that the logical
states are inverted.
Both devices feature dual thermal interrupt outputs (“high
limit” and “low limit”), each of which is programmed with a
single external resistor. With the TC620, these outputs are
driven active (high) when the measured temperature equals
Below, an application example using the TC620 is given.
Thanks to the two programmable temperatures, it is possible
to set an intermediate current level before turning the LED
module off completely.
3.3.1.6. Application solution 6 – TC620(1) solution
C1 = 100 nF 25 V 10 % X7R 0603
Q1, Q2 = NPN signal transistor (i.e. BC847)
R2 = 330 k1 5 % 0603
R3 = 330 k1 5 % 0603
Rset1
Rset2
RHS
RLS
Figure 22: Thermal derating – TC620 solution.
For more information, please see the general notes on page 33.
30
see example on the right
LEDset APPLICATIONS
Figure 23: TC620 solution – output characteristic.
Figure 24: TC620 solution – RTRIP vs. temperature.
Example:
Conditions:
TsetH = 80 °C
TsetL = 70 °C
In order to achieve the 70 % of Inommax, the equivalent parallel resistance RsetEQ (Rset1||Rset2) to be chosen must be
about 26.7 k1 (see table 4 in chapter 3.1.1.).
IoutH = 0 % Inommax
IoutL = 70 % Inommax
With the TC620 datasheet, it is possible to calculate the
resistance value for the temperature trip points:
RTRIP
0.5997 T
2.1312
(see figure 24)
Therefore:
RHS = 161.5 k1
RHS = 162 k1 (E96 1% series)
TsetH = 80.6 °C
RLS = 151.9 k1
RLS = 150 k1 (E96 1% series)
TsetL = 68.8 °C
RsetEQ
Rset1 Rset2
Rset1 + Rset2
26.7 kȍ
Rset2
Rset1 RsetEQ
Rset1 RsetEQ
61.8 kȍ
Rset2 = 61.9 k1
(E96 1 % series)
Recalculating, the real Iout = 70.2 % of Inommax.
Regarding Rset resistor:
Rset1 = 47 k1 1 % (100 % of Inommax – see chapter 3.1.1.)
31
LEDset APPLICATIONS
Note: For a precise calculation, the VCEsat of Q2 should also be considered. For a
BC847 transistor, the voltage drop is in the range between 40 and 50 mV depending
on the temperature of the device. In figure 25, the voltage drop relates to a temperature
range between -55 and +150 °C. In the described application solution, however, the
temperature of Q2 is generally within a tighter range when it is active. Therefore, the
voltage drop variation will be smaller than in figure 25.
The RsetEQ model should be as follows:
BC847B; lC/lB = 20.
(1) Tamb = 150 °C.
(2) Tamb = 25 °C.
(3) Tamb = -55 °C.
Figure 25: BC847 – collector-emitter saturation voltage vs. collector current
(NXP reference data).
Considering the calculated Rset1 and Rset2 and introducing a
voltage drop of Q1 = 45 mV :
Vset
Rset2 Iset + VCEsat
Rset2
1+
Rset1
7.37 V and therefore Iout = 70.4 % of Inommax
The error introduced by the transistor affects the overall control
accuracy of the ECG by about 0.2 % (to be added to the 5 % of the
ECG itself). The severity of the error depends on the working point
and the transistor Vce. Choosing a lower output current increases
the severity of the error (i.e. Iout = 35 % of Inommax
0.3 %).
32
LEDset APPLICATIONS
3.3.1.7. General notes on IC temperature switches:
choice and usage
• For all the above application solutions, the Rset can be
either a fixed resistor or a variable resistor usable for local
dimming (as described in 3.2.).
• For all the above application solutions except application
solution 6, the output of the IC (direct output or output via
transistor) can be connected to the Vset line via an Rset2
resistor. In this way, in case of overtemperature, the output
current can be set to a percentage of Inommax instead of
completely switching off the LED module as shown in the
example cases. Application solution 6 allows implementing
both conditions, partial load and switch-off control.
Figure 26: Two-step solution without switch-off.
• When choosing IC temperature switches, the following
issues must be considered:
– Leakage current of the output stage of the control
module: In case of an open-drain output solution directly
connected to Vset, the leakage current should be as low
as possible (10 μA already lead to an error of 3 %) in
order not to affect the overall control accuracy.
– Supply voltage: If the IC cannot withstand the +12 V,
a voltage regulator must be used.
– Supply current: In LEDset ECGs of the first generation,
the supply current provided by the +12Vset terminal must
be kept lower than 15 mA.
– Transistor output solution:
- Suitable if the maximum voltage of the output pin of the
IC cannot withstand the maximum Vset that applies to
the respective application.
- Suitable if the leakage current of the output pin of the
IC becomes too high (a leakage current of more than
10 μA affects the overall control accuracy of the ECG by
3 % (to be added to the 5 % of the ECG itself).
33
LEDset APPLICATIONS
3.3.2. Overtemperature protection (discrete NTC)
The application solutions analyzed in 3.3.1. show the implementation of the LED module’s overtemperature protection
by means of a dedicated IC chip that integrates the temperature sensing. Similar results can be achieved by implementing
electronic circuits based on a discrete NTC component and
an OPAMP (operation amplifier) which acts like a comparator.
Benefits of this solution:
• The cost of the circuit components is lower.
• In some applications, the sensing component needs to be
placed very close to the LED or in other places where
space can be a problem. The use of a discrete NTC
(i.e. an SMD NTC) can solve this issue.
• It allows the implementation of continuous derating
functions (not only steps of Iout).
Drawbacks:
• The NTC resistance variation needs to be converted into a
useful signal according to the operating range of the Vset
characteristic. This implies the need for a higher number of
(low-cost) components.
• Depending on the complexity, the tuning of the circuit design needs more time, especially concerning the variation
of the Vset output with respect to the tolerance of the discrete components used.
3.3.2.1. Application solution 1 –
overtemperature protection by comparator
This chapter shows how an overtemperature protection
circuit can be implemented by using an OPAMP IC in positive feedback configuration (acting like a comparator).
Figure 27: Thermal derating – NTC + OPAMP solution.
34
Figure 28: NTC + OPAMP solution – output characteristic.
LEDset APPLICATIONS
The circuit configuration allows setting a hysteresis between
on and off state, thus avoiding spurious and unwanted light
flickering/toggling: focusing on the comparator circuit, the
R1, R4 and R3 resistors set the trip threshold voltages VTRIP+
(related to TsetTH- 6THyst) and VTRIP- (related to TsetTH).
These VTRIP voltages are compared with the voltage
related to the divider realized by the R2 and NTC resistors.
Based on the NTC characteristic (resistance vs. temperature)
and the pull-up resistor (R2 in this case), it is possible to tune
the circuit to customer needs. Once the VNTC (voltage across
the NTC) becomes higher than VTRIP+, the comparator output
goes to low state. Consequently, Q1 opens and the LED
module is supplied by the current which has been set by the
Rset resistance.
However, when VNTC becomes lower than VTRIP-, the output
of the comparator turns on Q1 and thus the Iout becomes
0 mA.
2
Example:
Requirements:
TsetTH = 76 °C
6THyst = 6 °C
1
Iout = Inommax
Ioutfault = 0 mA
Figure 29: NTC + OPAMP solution – real circuit (1) appearance with
connector block (2).
By selecting the following components,
the result shown in figure 30 can be achieved:
R1 = 100 k1 0603 1 % (general purpose)
R2 = 270 k1 0603 1 % (general purpose)
R3 = 560 k1 0603 1 % (general purpose)
R4 = 36 k1 0603 1 % (general purpose)
Rset = 39 k1 0603 5 % (general purpose)
RNTC = NTCS0805E3683GXT (680 k1 2 % 0805) (glass-protected – Vishay)
U1 = LM2904M – SO8 (general purpose)
Q1 = BC847 – SOT23 (general purpose)
C1 = 100 nF X7R 0603 (general purpose)
(by-pass capacitor to be placed as close as possible to the power pins of U1)
Figure 30: Thermal derating – NTC + OPAMP solution (example).
35
LEDset APPLICATIONS
3.3.2.2. Application solution 2 –
overtemperature management by comparator: two-step output
The following application is basically similar to the one described in
chapter 3.3.1.6. Application solution 6 – TC620(1) solution. The
circuit is obtained by using a low-cost dual OPAMP, which allows
setting two trip temperatures (TsetH and TsetL) and their relative
hysteresis by extending the circuit functionality described in chapter
3.3.2.1. Application solution 1 – overtemperature protection by
comparator.
Figure 31: Thermal derating – NTC + OPAMP solution: two-step output – schematic.
36
Figure 32: NTC + OPAMP solution: two-step output – characteristic.
LEDset APPLICATIONS
Example:
Requirements:
TsetH = 70 °C
TsetL = 55 °C
6THyst = 5 °C
Iout = Inommax
Ioutwarning = 60 % Inommax
Ioutfault= 0 mA
By selecting the following components,
the result shown in figure 33 can be achieved:
R1 = 68.1 k1 0603 1 % (general purpose)
R2 = 270 k1 0603 1 % (general purpose)
R3 = 560 k1 0603 1 % (general purpose)
R4 = 20.5 k1 0603 1 % (general purpose)
R5 = 560 k1 0603 1 % (general purpose)
R6 = 36 k1 0603 1 % (general purpose)
Rset1 = 18 k1 0603 1 % (general purpose)
Rset2 = 22 k1 0603 1 % (general purpose)
RNTC = NTCS0805E3683GXT (680 k1 2 % 0805) (glass-protected – Vishay)
U1 = LM2904M – SO8 (general purpose)
Q1, Q2 = BC847 – SOT23 (general purpose)
C1, C2 = 100 nF X7R 0603 (general purpose)
(by-pass capacitor to be placed as close as possible to the power pins of U1)
Notes:
• Rset = Rset1 + Rset2 sets the Inom.
• The dividing rate between Rset1 and Rset2 allows adjusting the Ioutwarning
output level.
• The distribution of the resistance values of R1, R4 and R6 allows setting and
adjusting the TsetH and TsetL temperature trip thresholds.
• Adjusting the values of R5 (for TsetH) and R3 (for TsetL) allows changing the respective
6THyst (in principle, 6THyst can be set with different values for TsetH and TsetL).
Increasing the resistance value decreases the 6THyst and vice versa.
Figure 33: Thermal derating – NTC + OPAMP solution: two-step output (example).
2
1
Figure 34: NTC + OPAMP solution: two-step output – real circuit (1)
appearance with connector block (2).
37
LEDset APPLICATIONS
3.3.2.3. Application solution 3 –
overtemperature management: continuous derating and switch-off
The following application shows a cost-efficient solution obtained by using a lowcost dual OPAMP (such as LM2904). The idea is to manage the overtemperature
state of the LED module by continuously derating the current in a defined temperature range (from TsetL to TsetH), ending with the switch-off of the supply output
current when the protection temperature is reached (TsetH). The design of the
circuit becomes a bit more complicated but the solution is very cheap and only
requires about 15 components which do not take up a lot of space.
Figure 35: Thermal derating –
NTC + OPAMP solution: continuous derating and switch-off.
38
Figure 36: Thermal derating –
NTC + OPAMP solution: continuous derating and switch-off characteristic.
LEDset APPLICATIONS
Example:
Requirements:
TsetH = 75 °C
TsetL = 60 °C
6THyst = 5 °C
Iout = Inommax
Ioutwarning = from 100 % to 60 % Inommax in a linear way
Ioutfault= 0 mA
By selecting the following components,
the result shown in figure 37 can be achieved:
R1 = 100 k1 0603 1 % (general purpose)
R2 = 270 k1 0603 1 % (general purpose)
R3 = 0R 0603 1 % (general purpose)
R4 = 681 k1 0603 1 % (general purpose)
R5 = 36.8 k1 0603 1 % (general purpose)
R6 = Not mounted (general purpose)
Rset1 = 18 k1 0603 1 % (general purpose)
Rset2 = 22 k1 0603 1 % (general purpose)
Rset3 = Not mounted
RNTC = NTCS0805E3683GXT (680 k1 2 % 0805) (glass-protected – Vishay)
D1 = 1N4148 (general purpose)
U1 = LM2904M – SO8 (general purpose)
Q1 = BC847 – SOT23 (general purpose)
C1, C2 = 100 nF X7R 0603 (general purpose)
(by-pass capacitor to be placed as close as possible to the power pins of U1)
C3 = 1 nF COG 0603 (general purpose)
(by-pass capacitor to be placed across D1)
Notes:
• Rset = Rset1 + Rset2 sets the Inom.
• The dividing rate between Rset1 and Rset2 allows adjusting the Ioutwarning output slope
level.
• The distribution of the resistance values of R1, R2 and R5 allows setting and
adjusting the TsetH and TsetL temperature trip thresholds.
• Moving the values of R4 allows adjusting the respective 6THyst. Increasing the
resistance value decreases the 6THyst and vice versa.
Figure 37: Thermal derating – NTC + OPAMP solution: continuous derating and
switch-off characteristic (example).
2
1
Figure 38: NTC + OPAMP solution: continuous derating and switch-off –
real circuit (1) appearance with connector block (2).
39
LEDset APPLICATIONS
3.3.2.4. Application solution 4 –
LEDset and current set combination: direct NTC connection
As described in chapter 3.2.2.3. General notes on local dimming: LEDset,
“current set” combination, there are ECGs which can combine the LEDset interface characteristic with the optional current set configuration. ECGs with this kind
of combination offer another very simple and economical application: the direct
connection of an NTC. Additional resistors named Rs and Rp can be used to finetune the TsetTH and the linearization of the characteristic above the TsetTH.
Figure 39: Thermal derating – direct NTC connection.
40
Figure 40: Direct NTC connection – output characteristic.
LEDset APPLICATIONS
For this kind of application, the choice of the NTC is fundamental to meet the requirements in terms of the TsetTH
(temperature from which to start the derating) and the slope
rate (based on the NTC parameters B25/85 and B25/100) of
the characteristic Iout vs. Tset above the TsetTH. For the fine
tuning, the Rp resistor allows changing the TsetTH point to
reach the temperature required to start the derating.
Example:
The following example shows the result that can be achieved
by using a standard SMD NTC component from a well-known
NTC thermistor producer.
Rs = 0 1 (short circuit only)
RNTC = NCP15WM474J03RC
(470 k1 3 % B25/85 = 4582 - 0805 - Murata)
Two curves are shown to highlight the effect of the Rp resistor on the
determination of the TsetTH. The following Rp values have been used:
Rp1 = 270 k1 0603 1 % (general purpose)
Rp2 = 120 k1 0603 1 % (general purpose)
Figure 41: Thermal derating – direct NTC connection (example).
41
LEDset APPLICATIONS
3.3.2.5. Application solution 5 – overtemperature
management: microcontroller (MCU) approach
Since the cost of small 8-bit microcontrollers has dropped
over the past years, they have become an affordable solution
for implementing simple functionalities and increasing the
flexibility of a system at the same time. These microcontrollers are equipped with various kinds of peripherals, e.g.
A/D converters (8–10 bits), which allow the measurement of
analog input coming from an NTC, as well as a light sensing
circuit. I2C or UART-embedded HW peripherals allow exchanging data via a communication bus or interfacing other
ICs (e.g. light sensors such as SFH7770 can be directly connected via I2C bus).
In terms of temperature/overtemperature management,
this type of MCU (e.g. Microchip PIC12F1822 or Atmel
Tiny25/45) offers a high level of flexibility as it can be
programmed to achieve different goals:
Different NTC sensors can be interfaced by saving different
NTC characteristics in the MCU memory.
• The NTC signal can be “transformed” into Vset output (and
therefore Iout) via a very flexible and fully customizable relation.
• Some MCUs, e.g. the types mentioned on the left, have an
embedded temperature sensor which can be used to evaluate the temperature of the LED module. In this way, it is
possible to save MCU resources/pins for other functions
such as sensing inputs.
• Information on the LED module and the luminaire, e.g.
current temperature value, set-up parameters and warning
temperature, can be communicated to the user in various
smart ways: via digital bus (by wire), by infrared receiver
and transmitter or by using an LED coding approach (e.g.
turning a dedicated LED on and off at a certain frequency).
• The LED module itself can be used to warn the user in
advance of a possible overtemperature problem. For this
purpose, the LED module can be put into “blinking” mode
by turning the light on and off or switching it between its
maximum and minimum level (see figure 43).
This MCU approach is illustrated by the schematic diagram
on the right.
42
LEDset APPLICATIONS
Note:
The DAC interface can be implemented in various ways. The only
thing to take into account is that the DAC circuit must be able to
sink the Iset current (274 μA) imposed by the Vset connection.
Figure 42: Thermal derating – MCU solution.
A simple voltage regulator is required to regulate the +12Vset to 5 V which
are needed to supply the MCU.
The voltage divider R2/NTC is connected to the same 5 V supply as the MCU.
The middle point of the divider is connected to an A/D channel of the MCU.
On the output side, the PWM output used to generate the
Vset is connected to a filter (active or passive) to rectify the
signal. In the example (figure 42), only a general DAC interface block is shown. DAC output is sensed by an A/D channel of the MCU, thus controlling the Vset output in a closedloop system, which ensures the highest accuracy of the output.
In the MCU memory (ROM or EEPROM if present), the NTC
divider characteristic can be stored as a lookup table. Here
are some notes on this:
• The higher the number of the stored points, the more accurate is the output of the measurement.
• If the measured temperature is between two points, an interpolation can be used.
• The number of lookup table points should be higher in the
region of interest (i.e. if the overtemperature is 70 °C, the
number of points should be higher between 60 and 80 °C).
• A higher AD resolution improves the accuracy of the measurement but also affects the memory resources.
• A little digital filter should be applied on the AD raw values
if no external hardware filter is used on this input (RC filter).
Once the filtered AD1 count value is translated into a temperature value by the stored temperature lookup table, the Vset
reference value must be generated. For converting the temperature value into a Vset value, another lookup table (e.g.
Vset lookup table) has to be used.
The output result is used as a reference to generate the duty
cycle of the PWM channel corrected by the feedback coming from the AD2 channel.
43
LEDset APPLICATIONS
Using two lookup tables – one for the temperature and one
for the Vset – allows the designer to be very flexible:
• The NTC can be changed by modifying only the points of
the temperature lookup table.
• The Vset output characteristic can be changed (e.g. when
the temperature monitor system is used for a different luminaire) by modifying only the points of the Vset lookup table.
• By storing more than one lookup table for the temperature
and the Vset (the only limitation is the available memory
size), more applications can be covered by the same MCU
and the same firmware. In this case, the correct table configuration has to be selected by pulling one or more MCU
pins at +5 V or GND.
• Since the Vset output is generated digitally by the MCU,
it is possible to toggle it between two values in a certain
temperature range and with a chosen frequency (low
enough to be far from the cut-off frequency of the pass
band of the used ECG), generating a light toggling if necessary. The example below (figure 43) shows a possible
Figure 43: Example of overtemperature warning by LED module toggling.
44
implementation. Reaching the determined temperature before the overtemperature protection value, a toggling between two current levels (e.g. 100–50 % or 100–0 %) allows the luminaire to warn the user about a possible shutdown situation.
• A simpler way to signalize the LED module status can be
provided by a small colored LED (e.g. blue LED) connected
to a general-purpose output pin of the MCU. This LED can
be placed directly on the LED module or somewhere else
in the luminaire.
• A UART communication interface (see figure 44) realized
by an IR emitter diode and an IR transistor receiver (e.g.
SFH320FA) allows the digital communication of the luminaire status and enables the manufacturer to customize
the luminaire directly at the end of the production line (i.e.
by downloading the lookup tables) or even to upgrade the
luminaire system behavior after installation (see figure 45).
Moreover, the IR emitter diode and IR transistor receiver
can be placed directly on the LED module (option 1) or in
a different, more convenient space of the luminaire system
(option 2).
LEDset APPLICATIONS
Figure 44: Thermal derating – MCU solution: module status signaling by an LED.
Figure 45: MCU solution: module status signaling/communication by IR interface.
The MCU approach can be a bit more expensive and may
require more design development skills (need of HW and
SW development) compared to the application solutions
discussed earlier in this chapter. However, together with
OSRAM ECGs equipped with LEDset interface, it significantly
increases the customizability and flexibility of the luminaire
system.
45
LEDset APPLICATIONS
3.4. +12Vset auxiliary supply
3.4.1. Aesthetic use
The LEDset interface provides a +12Vset supply voltage that
can be used in different ways: not only for thermal management, daylight compensation and aging compensation, but
also for aesthetic purposes.
In addition to supplying the circuits shown above, the
+12Vset supply voltage can also be used for some “lowpower” LED applications, e.g. ring backlighting of a luminaire
switch (see figure 48).
Figure 46: +12Vset auxiliary supply – aesthetic use.
Figure 47: +12Vset auxiliary supply – aesthetic use, controlled LEDs.
CHIPLED or TOPLED low-power LEDs can be supplied by
connecting them directly to the +12Vset via a resistor (see
figure 46) or, in case of an MCU application, via a MOSFET/
transistor that can add a blinking feature or a smooth pulsing
solution (by using a PWM output of the MCU; see figure 47).
A ring-shaped light guide, for example, can create very nice
aesthetic effects without requiring an additional power supply.
46
Figure 48: Application example:
ring backlighting of a luminaire switch.
LEDset APPLICATIONS
3.4.2. Active cooling
Future generations of the LEDset interface might have a
higher power capability via the +12Vset auxiliary supply.
It will then be possible to drive an active cooling system
such as a fan (e.g. when high-power LED modules require
forced cooling). The following block diagram shows such
an application.
Figure 49: +12Vset auxiliary supply – active cooling system.
The power supplied by the +12Vset auxiliary supply and thus
the cooling capability of the fan can be regulated by an external electronic control circuit, with the LED module temperature being used as control signal. This feature can be easily
and flexibly integrated with a small MCU on the LED module.
Please refer to the datasheet of the LEDset product and
verify that the current capability of the +12Vset auxiliary
supply matches the selected fan requirements.
47
LEDset APPLICATIONS
3.5. Constant lumen output
The application example in chapter 3.3.2.5. Application
solution 4 – overtemperature management: microcontroller
approach shows that – in addition to the thermal management of the module – more features can be added thanks
to the presence of the MCU:
• By using a general-purpose timer of the MCU, it is possible
to measure the working time of the module and store it to
memory.
• The real-time temperature measurement allows the application of a “temperature weight” to properly estimate the
lifetime of the module.
• The knowledge of the real supply current of the LED module allows the application of a “current weight” to properly
estimate the lifetime of the module.
By estimating the lifetime of the module with the mentioned inputs (estimation algorithms are not within the scope of this application guide), it is possible to increase
the nominal output current of the ECG to a certain degree (up to its maximum limit)
by increasing the Vset control voltage, thus compensating the aging effects of the LED
module as shown by the orange line in figure 50 (the dashed gray line illustrates the
luminous flux decrement that occurs if the aging effects are not compensated).
The concept explained above can be implemented by storing a constant-lumen lookup
table in the MCU memory. By entering the working time of the module (e.g. in kHours),
it is possible to achieve the increase in Vset control voltage required to compensate the
aging effects of the LED module. The working time can be regularly saved in the MCU
memory (e.g. EEPROM), thus providing an accurate estimation of the lifetime.
Figure 50: Aging compensation: characteristic of concept.
48
LEDset APPLICATIONS
3.6. Combination of features
With LEDset, some LED control features can be combined
with one single interface. Figure 51 gives an overview of possible combinations. OSRAM will assist you in creating your
own specific solution.
Features that can be combined:
• Temperature control
• Daylight sensing
• Local dimming by potentiometer
(connected to the control module)
• Use of external switch for on/off switching
(e.g. capacitive touch key)
• Aging compensation
• Auxiliary LED signaling
• Auxiliary IR communication
Figure 51: Combination of LED control features by MCU via LEDset interface.
49
www.osram.com/ledset
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