SMPS for low end TV set with VIPer53

SMPS for low end TV set with VIPer53
AN1865
- APPLICATION NOTE
®
SMPS FOR LOW END TV SET WITH VIPer53
F. GENNARO - C. SPINI
ABSTRACT
In this paper a low cost power supply for 90º TV set (14" to 21") is introduced. The converter uses the
new VIPower device VIPer53 in DCM Flyback configuration with either primary or secondary regulation.
It provides 60W peak output power on 3 isolated outputs using a DIP-8 package device. The power
supply has been specifically developed for European input range.
INTRODUCTION
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The VIPer is a family of integrated smart power IC that makes easier size and cost optimization in switch
mode power supplies. The devices are based on PWM current mode control and provide integrated
high-voltage start-up circuit and protections such as current limiting, thermal shutdown and over/under
voltage detection.
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VIPer53 represents the latest generation of VIPer family and uses multichip approach in chip to chip
fashion to integrate in a single package a PWM controller in VIPower M0 technology and a 620V
MDMesh Power MOSFET. It is housed in DIP-8 and PowerSO-10 package for through-hole or SMD
mounting. Although the Mosfet is based on the standard MDMesh technology, it features integrated
current sense by means of a SenseFET in order to perform current mode control, avoiding the use of an
external sensing resistor.
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One more feature has been introduced in this last generation: the overload control, by means of a
dedicated pin TOVL, which allows to manage the overload event regardless of transformer quality in
hiccup mode.
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The power supply provides 3 isolated outputs: 105/115V dedicated to the deflection, 13V dedicated to
the audio and a 6.5V dedicated to the µP. The first output can be set to either 105V or 115V by means of
a jumper in order to properly drive the 14"-21" CRT yokes. A trimmer allows manual adjustment of the
output voltage. The feedback is typically taken at primary side, on the auxiliary winding of the
transformer, but isolated secondary regulation on the 105/115V output can be arranged on the proposed
board by means of optocoupler. Both regulations use TL431 in the feedback loop. The power supply
has been specifically developed for European input range, i.e. 185-265Vac.
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1. APPLICATION DESCRIPTION AND DESIGN
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The proposed power supply has been designed referenced to the specifications listed in Table 1. The
switching frequency has been selected considering transformer size, power losses and EMI behaviour,
since according to EN55022 standard for conducted emissions the harmonics to be evaluated are in the
range from 150kHz to 30MHz.
The target efficiency is higher than 70% with a maximum duty cycle of 45% at minimum input voltage,
always in discontinuous conduction mode.
Primary or secondary regulation can be performed and both regulations use TL431 to provide trimmable
voltage reference for the 105V/115V output. The other two outputs take advantage of transformer cross
regulation by means of optimized winding layout. The 5V output is post-regulated using a standard
linear voltage regulator for high accuracy and stability.
May 2004
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AN1865 - APPLICATION NOTE
The input EMI filter consists in a Pi-filter for both differential and common mode emissions. A standard
RCD circuit connected to ground is used to limit dv/dt of the drain voltage for noise issue in the TV set.
Moreover, a light RCD clamper is connected to the drain in conjunction with a peak clamp for the peak
voltage management during transient conditions, as shown in the schematic in Figure 3.
The VIPer makes power supply design easier considering start-up, current sensing and no-load issues,
improving the overall efficiency and simplifying the circuit. The short circuit protection is provided with
hiccup mode and overload is controlled by TOVL pin. However an input 5*20 fuse is used to protect the
system against catastrophic failures. The input section also has an NTC to limit the inrush current of the
bulk capacitor during the start-up of the power supply.
The switching frequency is set by R5 and C16 according to the diagram given in the datasheet. C13 is
the VIPer supply capacitor connected on VDD pin.
Moreover, VIPer53 has a built-in burst mode circuit that allows cycle skipping under low load condition,
improving stand-by performance. Such a control has been improved compared to the old VIPer
generation using a variable blanking time: 150 or 400 ns.
Table 1: SMPS Specifications
Input voltage
Output power (peak)
Outputs
Out1
185-265 Vac
60W
3
105V/115V at 450mA; P1=47.3W, 2%
Out2
13V at 600mA; P2=9.1W, 2%
6.5V at 80mA; P3=0.52W, 2%
50 kHz
Out3
Switching frequency
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1.1 FLYBACK TRANSFORMER
In the considered application the Flyback transformer has 5 windings, since one winding is dedicated to
supply the VIPer, as listed in table 2. Winding arrangement is shown in Figure 1, while transformer pinout and dimension are shown in Figure 1. Due to the presence of 105V/115V output, the reflected
voltage has been set to 120V. The transformer is a slot type with ETD34 core, manufactured by TDK. A
layer type transformer can be used as well, as shown in Figure 3.
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Table 2: SMPS Specifications
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Core
Primary inductance Lp
Leakage inductance
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Output 105V
Output 115V
Output 13V
Output 6.5V
Aux
2/16
ETD34 TDK
740µH ± 10%63 turns
15µH max1.8% Lp
Windings specs
48 turns
53 turns
6 turns
3 turns
6 turns
AN1865 - APPLICATION NOTE
Figure 1: Transformer layout
7
2
115V
4
PRIMARY
105V
3
6
8
6.5V
10
14
11
13V
AUX
13
12
PRIMARY SIDE
SECONDARY SIDE
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Figure 2: Transformer pin out and dimensions
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Figure 3: Transformers
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AN1865 - APPLICATION NOTE
1.2 VOLTAGE FEEDBACK
Voltage feedback is realized either in primary or secondary side. Both configurations use TL431 with a
trimmer in the voltage divider network to adjust the reference voltage, as shown in figure 5. In primary
regulation, the auxiliary winding provides both the supply voltage to the VIPer and the regulation voltage
using two separated circuits, by means of two rectifier diodes, as shown in the schematic. In particular,
R7 and D6 provide the supply voltage while R21 and D9 provide the regulation voltage. Doing so, it is
possible to get good regulation at minimum load, with consequent improvement of the stand-by
performance, and to easily provide short circuit protection in hiccup mode.
The board has been developed on a 125x80mm Cu single side 70µm FR-4 frame, as shown in figure 4.
Figure 4: PCB layout
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AN1865 - APPLICATION NOTE
Figure 5: Circuit schematic
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AN1865 - APPLICATION NOTE
Table 3: Component list
Reference
F1
R1
R2
R3
R4
R5
R6
R7
R8
R9
R10
R11
R12
R13
R14
R15
R16
R17
R18
R19
R20
R21
R22
RS
C1
C2
C3
C4
C5
C6
C7
C8
C9
C10
C11
C12
C13
C14
C15
C16
C17
C18
C19
C20
C21
C22
C23
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Note
For secondary regulation
Not connected
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Description
T2AL250V Fuse 5x20
NTC
10KΩ
3.3KΩ
330KΩ
6.8KΩ
22Ω
4.7Ω
91Ω
68KΩ
4.7KΩ
47KΩ
12KΩ
1KΩ Trimmer
2.2KΩ
1KΩ Trimmer
2.2KΩ
120KΩ
10KΩ
220Ω
0Ω
150Ω
47Ω
3.3Ω 3W dv/dt Limiter Resistor
100nF - 250V X2 Capacitor
100nF - 250V X2 Capacitor
1nF - 250V
1nF - 250V
47µF - 400V
1nF - 600V
330nF - 25V
47µF - 200V
4.7µF - 200V
470µF - 25V
100nF - 25V
100nF - 25V
10µF - 25V
1000µF - 35V
100µF - 35V
4.7nF - 25V
10nF - 25V
100nF - 25V
330nF - 25V
2.2nF - 250V Y1 Capacitor
100nF - 25V
100 nF - 200V
100nF - 25V
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AN1865 - APPLICATION NOTE
Table 3: Component list (continued)
Reference
Description
100µF - 16V
220pF
100nF - 25V
220pF - 600V dv/dt Limiter Capacitor
DF06M 1A - 600V
STTH106
STMicroelectronics P6KE180A
1N4148
STMicroelectronics STTH106
STMicroelectronics 1N5819
STMicroelectronics STTH302
STMicroelectronics STTH106
1N4148
330nH
TDK SRW34ETD8-E03V0121
TDK SRW35EC-T89V017
15mH S+M B82732
STMicroelectronics VIPer53DIP
STMicroelectronics TL431
TCDT102G
STMicroelectronics TL431
STMicroelectronics LE50CZ
C24
C25
C26
CS
D1
D2
D3
D4
D5
D6
D7
DS
D9
L1
T1
T2
U1
U2
U3
U4
U5
Figure 6: Board
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Layer
Slot
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AN1865 - APPLICATION NOTE
2. LAYOUT RECOMMENDATION
Since EMI issues are strongly related to layout, a basic rule has to be considered in high current path
routing, i.e. the current loop area has to be minimized. In particular, such a rule has to be applied to the
input filter section, the clamper and the dv/dt limiter sections
One more consideration has to be done regarding the ground connection: in fact in order to avoid any
noise interference on VIPer logic pins the control ground has to be separated from power the ground.
This results in a dedicated track for ground connection of C12, C13, C16, C17, C18, U2 anode and U3
collector.
3. EXPERIMENTAL RESULTS
3.1 - PERFORMANCES AND TYPICAL WAVEFORMS
The performances of the power supply have been evaluated only using primary regulation, in terms of
voltage regulation and power consumption. The board can also be configured for secondary regulation,
even if this is not typical for such a TV set. Finally typical waveforms are shown.
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In Table 4 and 5 the main experimental results on 14" and 21" chassis are listed. The converter features
excellent voltage regulation as the input voltage changes, with low power consumption at no load and
efficiency as high as 87% at full load. In Figure 7 the drain voltage VDS at no-load and different input
voltage Vin is shown; the automatic burst mode management is evident. In Figure 8 the drain voltage
VDS at full load is shown at 185VAC and 265VAC input voltage, respectively, in order to evaluate the
maximum duty cycle and the maximum drain voltage under nominal operation. In Figure 9 V DS and VDD
during start-up at 230VAC and typical load are shown, while in Figure 10 V DS and Vout3 during start-up
265VAC with stand-by load and full load are shown, respectively. Thanks to the internal current
generator, which provides constant current, the start up time is independent of the input voltage and only
depends on the VDD capacitor value.
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In Figure 11 the dynamic load regulation is shown as a step load variation is applied on the audio and
both audio and video output, respectively.
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Table 4: TV chassis typical consumptions
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14”
21”
mA
Pout
Pin
V
mA
Pout
Pin
34.4W
42W
105.6
380
49W
57W
V1
H. Deflection
100.3
274
V2
µP and logic
7.7
230
8.3
260
V3
Audio
10.4
500
11.3
600
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These measurements have been performed applying an average video consumption (like an average
real TV picture) and maximum audio output driven by a sinewave signal at 3KHz.
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In order to allow the normal operation of the TV chassis a slight modification is required: as the output
voltage V2 drops from 8.3V to 6V, the standard linear regulator on the chassis is changed with an LDO
type.
The same set of test has been performed on boards with both kinds of transformers, i.e. slot and layer
type. As shown in Table 5 the power supply performances are similar with both transformers, the picture
stability (screen modulation) due to the audio load variation is good too. The two kinds of transformers
can be used on the same board assuring the same performance: the only difference related to the
transformer construction is the use of a small RC snubber across D7 using the slot transformer because
of the minimum 20% margin required by the diode VRRM, since it damps the voltage ringing across the
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AN1865 - APPLICATION NOTE
diode. Such an adjustment has led to lower dv/dt value of the drain voltage, as shown in Figure 12, and
consequently to lower radiated noise level which has its importance in the case of low antenna signal
(typical for portable TV set).
Table 5: Power measurements with 21” TV chassis in normal operation at 230Vac
Normal operation at 230VAC
SLOT
LAYER
V
mA
V1
105.4
380
V2
6.24
262
V3
12.5
610
V1
103.9
378
V2
6.16
265
V3
12.62
600
Pin
Pout
Efficiency
56.47
49.3
87.3%
55.34
48.47
87.6%
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Figure 7: V DS at no load
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Vin=185VAC
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Vin=230VAC
Vin=265VAC
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AN1865 - APPLICATION NOTE
Figure 8: V DS at full load
Vin=185VAC
Vin=265VAC
Figure 9: V DS and VDD during start-up at 230VAC and typical load
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Figure 10: V DS during start-up at 230VAC: stand-by and full load
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Figure 11: Dynamic load regulation at Vin=230VAC
CH2=V13V, CH3=V115V, CH4=I13V=100/600mA,
I115V=380mA, I5V=260mA
CH2=V13V, CH3=V115V, CH4=I13V=100/600mA,
I115V=200/380mA, I5V=260mA
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Figure 12: Drain voltage dv/dt at Vin=325VDC and full load, using slot and layer transformers
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3.2 STAND-BY PERFORMANCE
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Typical waveforms of the circuit with nominal stand-by load have been shown in figure 7. During such a
load condition, the power supply operates in burst mode thanks to the internal control circuit of the
VIPer53, which allows power consumption saving due to lower switching losses. Inside the burst the
maximum switching frequency is the nominal, fixed by the RC connected to OSC pin of the VIPer.
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VIPer53 features improve stand-by performance thanks to variable blanking time, which is made longer,
i.e 400ns, than the normal mode value, i.e. 150ns, during burst mode. This change is triggered
according to COMP pin voltage: if VCOMP>1V the blanking time is set to 150ns typical, while it is set to
400ns typical if 0.5V<VCOMP<1V. Finally if 0<VCOMP<0.5V the device stops switching.
Power consumption measurements have been performed supplying the board by means of a DC source,
slightly overestimating the real application consumption since the DC measurements are typically higher
than in AC. As a final test on stand-by performance, the transition from stand-by to full load and viceversa
have been tested, in order to check the control circuit stability. As shown in figure 13, in spite of a fast
change in the current on the high voltage output, both the low voltage output and the auxiliary voltage do
not present any unstable behavior, insuring proper operation of the power supply.
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AN1865 - APPLICATION NOTE
The power consumption during the TV stand-by operation has been measured with both transformers:
the measured values are similar using both slot and layer type, as listed in Table 6.
Of course, using secondary regulation the input power consumption would be considerably reduced,
since the output voltages will be regulated at lower values.
Table 6: Stand-by measurements
SLOT
V1
V2
V3
STAND-BY at 230Vac
V
mA
153.8
0
8.4
50
18.54
0
LAYER
V1
V2
V3
153.3
8.2
18.59
0
50
0
Pin [W]
2.4
Pout [W]
0.42
2.35
0.41
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Figure 13: Waveforms during stand-by to full load and viceversa transitions at Vin=230VAC
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3.3 SHORT CIRCUIT BEHAVIOUR
The short circuit behavior has been considered for the three outputs shorting them one by one. Figure
14 shows the VIPer53 typical waveforms behavior during the short circuit. When a short occurs the
controller enters hiccup mode, working only for a short period as shown in the figure. This behavior limits
the average power dissipation of all the devices, preventing dangerous overheating and catastrophic
failures of the SMPS.
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VIPer53 features a new integrated overload control circuit, which is implemented on the TOVL pin and
does not lie on the transformer coupling quality between output and auxiliary for hiccup mode. In fact,
the device monitors the COMP pin voltage and as soon as its value is higher than 4.35V, an internal
current source is activated to charge up the T OVL capacitor, until the voltage across this latter pin reaches
4.0V. This is the threshold voltage to stop switching cycle and V DD voltage will decrease below VDDoff
value, thus entering hiccup mode with a controlled duty cycle. In any case, if VCOMP goes below the OVL
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AN1865 - APPLICATION NOTE
threshold, normal operation conditions are resumed. It is important to point out that the maximum value
of the peak drain current to consider for design purpose is the I DMAX, called drain current capability,
which is the maximum drain current that does not trigger the overload protection and defines the
maximum output power that the power supply can deliver.
Some constraints have to be considered for T OVL capacitor design, since the start-up of the power supply
do not have to be influenced. The following condition has to be checked regarding TOVL and VDD
capacitors:
COVL > 12.5 ⋅ 10 −6 ⋅ tSS
 1
 C
⋅I
C VDD > 8 ⋅ 10 − 4 ⋅ 
− 1 ⋅ OVL DDch 2
D
V
DDhyst
 RST

I DD1 ⋅ t SS
CVDD >
VDDhyst
where t SS is the rise time of the output voltage, DRST is the re-start duty cycle under short circuit or
overload conditions, IDD1 is the operating supply current during switching, IDDch2 is the start up charging
current for V DD higher than 5V and VDDhyst is the VDD start up threshold. The last 4 parameters are
defined in the datasheet.
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With such a selection of the two capacitors a proper start up of the power supply is guaranteed and a
typical 10% of restart duty cycle is achieved, avoiding overheating of both the transformer and the output
diodes and consequently catastrophic failure.
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3.4 OPEN LOOP FAILURE
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Open loop failure has also been considered as a faulty operation. Under such a condition the device will
control the output voltage thanks to the presence of a fast internal error amplifier, which starts working as
soon as the VDD voltage reaches 15V. This loop regulates the auxiliary voltage at 15V thus maintaining
the deflection voltage below the regulation value and avoiding the X-ray emission by an abnormal EHT
voltage applied to the CRT anode.
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Figure 14: Typical waveforms during short circuit at Vin=230VAC
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3.5 EMI MEASUREMENTS
Conducted EMI measurements have been performed according to EN55022 Class B standard, using a
50W LISN and a spectrum analyzer. The quasi peak conducted noise measurements with the power
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AN1865 - APPLICATION NOTE
supply connected to the 14" chassis has been performed at full load condition and nominal 230Vac input
voltage; the results are shown in figures 15 and 16. The measurements have been taken both on the line
(L1) and neutral (L2) conductors. In both conditions the power supply has passed the pre-compliance
test on conducted emissions.
Figure 15: L1 and L2 quasi peak measurements V IN=230VAC - 50Hz, with slot transformer
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Figure 16: L1 and L2 quasi peak measurements V IN=230VAC - 50Hz, with layer transformer
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3.6 THERMAL MEASUREMENTS
Temperature measurements have been performed in order to provide reliable operation condition for all
the circuit components. In Table 7the measured values with Tamb=23°C are listed. The VIPer53 in DIP-8
package takes advantage of the small copper area connected to the drain pin to act as a heat sink.
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Table 7: Main component temperature at full load
Device
T at 230VAC
VIPer53
68
R snubber
65
C snubber
42
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AN1865 - APPLICATION NOTE
D7 (105/115V)
59
D8 (5V)
35
D9 (13V)
43
Transformer
34
Bridge
58
4. CONCLUSIONS
In this paper an SMPS for 90º TV has been introduced and analyzed. Thanks to VIPer53 features the
design of the power supply is really straightforward, yielding to a cost effective solution.
The built-in functions and protections of the VIPer53 reduce the external component count, simplifying
the overall circuit. Recently introduced features improve both stand-by and overload operations.
Moreover, EMI behavior and thermal performance allow the use of standard components and materials
for the PCB, keeping the cost of the whole system low.
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The voltage regulation performance confirms the VIPer53 as the device of choice for low cost high
performance power supplies as required by the low end TV set market.
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For further information please visit STMicroelectronics VIPower web site: www.st.com/vipower.
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AN1865 - APPLICATION NOTE
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