Uninterruptable Power Supply Design using Float and Boost
International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 03 Issue: 07 | July-2016
p-ISSN: 2395-0072
R.Shalini1, A.N.Nagashree2, B.G.Ananthamurthy3
1 M.Tech
student, Dept. of Electrical and Electronics Engineering, BMS College of Engineering, Bangalore, India.
Professor, Dept. of Electrical and Electronics Engineering, BMS College of Engineering, Bangalore, India.
3General Manager, Dept. of Microwave, Alpha Design Technologies Pvt. Ltd, Bangalore, India.
---------------------------------------------------------------------***--------------------------------------------------------------------charges the battery. This charged battery acts as a
Abstract - In Military and Defence applications,
backup to drive the load when AC mains are OFF. As
Power supplies are of most important component. Usually,
Uninterruptable power sources (UPS) with constant output
the battery gets charged, its charging current reduces
voltage is required for continuous operation. In the recent
gradually. The float charger senses the reduction in
years, UPS is designed using a new technology called Float
charging current and reduces the charging voltage. If
cum Boost Charger (FCBC). FCBC is basically an UPS for ULSB
the battery gets drained, the float charger will again
MK-III devices which operates on 48V DC. In the present work,
increase the charging voltage and the process
FCBC is used for delivering regulated output voltage of 48V DC
continues [3].
at 4 Amps when loaded fully. Alternatively, a battery backup is
also provided wherein, the battery is charged when AC mains
is present. Even when the 230V Power supply is OFF, charged
battery backup of 24V 6Amps is sufficient to deliver the
required output voltage. Therefore, the entire system operates
continuously with a constant voltage of 48V DC. The efficiency
of the FCBC module was also well within the specified limits
which indicated that use of FCBC is a good alternate for the
conventional UPS systems.
1.2 Boost mode of operation
Boost charging involves a high current for short
period of time to charge the battery. It is generally used
if the battery has been discharged heavily. Boost
charging enables the quick charging of the depleted
batteries [3].
Key Words: Battery, Float Cum Boost Charger, Unit
Level Switch Board, Uninterruptable Power Supply.
Input voltage variation
Lower voltage cutoff
Upper voltage cutoff
Output voltage
Output rated current
Efficiency in Battery mode
Efficiency in AC mode
Power supply units are a must for functioning of any
electrical equipment. To reduce the risk of power
supply distortion, Uninterruptible Power Supply (UPS)
systems are often incorporated in electrical equipment
[1]. An UPS is designed to provide a battery-based
source of AC power, such that under mains fail
conditions the load can be supported for a specified
period of time [2]. In military and defence applications,
AC supplies are not preferred because continuous
power supply is of Utmost importance. Therefore, this
problem is overcome by using DC power supplies. For
this Purpose, Float Cum Boost Charger (FCBC power
supply module) is used [1, 2]. This work focuses on
providing a regulated output voltage through the
design, functionality and practical performance of
FCBC. In this work efficiency, is the main parameter
under consideration.
: 150V AC to 300V AC
: ≤150V AC
: ≥300V AC
: 48±2V DC
: 4±1 Amps
: 75% (approximately)
: 50% (approximately)
Float Cum Boost Charger (FCBC) is a switched
mode module capable of delivering regulated voltage of
48V at 4Amps when loaded fully. ULSB MK-III
equipment operates at 48V DC. As the equipment is
required to provide uninterrupted service to the
subscribers, the FCBC provides 48V DC to the ULSB
MK-III from an AC mains of 150V to 300V, 50Hz and in
case of mains power failure the FCBC provides 48V DC
to the equipment using battery bank of 24V connected
to the FCBC. The change over from AC to DC is
automatically done in case of power failure condition.
The block diagram of FCBC is shown in Fig 1.
1.1 Float mode of operation
In Float mode, FCBC supplies DC voltage required
to drive the load continuously and it also trickle
© 2016, IRJET
Impact Factor value: 4.45
ISO 9001:2008 Certified Journal
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International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 03 Issue: 07 | July-2016
p-ISSN: 2395-0072
microcontroller (PIC16F877A) to sense, control and
indicate the status of the FCBC during operation [4].
3.1 Modes of operation
There are two modes of operation of FCBC. They are
I) AC/Battery Mode
II) Battery charging Mode
The block diagram of AC/Battery Mode is shown in
Fig -1: Block diagram of FCBC
A secondary transformer of two independent windings
is connected directly after the fuse of AC mains supply.
It outputs a nominal DC voltage of 21V from 220V AC
through the bridge rectifiers. The input AC is applied to
FCBC through EMI filters to bridge rectifier which
converts 300VAC to 300V DC. The rectified DC is fed to
DC-DC converter (U3) and a ripple filter. The output of
ripple filter is passed to output via current sensor for
purpose of over voltage and load current protection.
During operation on AC mains supply, this current
sensor protects the unit against overvoltage, excessive
load current. If battery is connected when AC mains
supply is ON, the rectified 300V DC is applied to DC-DC
Converter (U7) for converting to 24V and is fed to
battery to charge it. Relay RL1 is used to enable
charging circuit whenever the battery potential is
below 20V [4]. In the absence of AC mains, 24V battery
voltage is applied to DC-DC Converter (U8) for
conversion of 24V to 48V. This voltage is passed
through current sensor. The current sensor gets
activated and provides protection against overload and
short-circuits. One output of the secondary winding is
used to sense the input mains variation during AC
mains operation. The output of this winding follows the
variation on the mains supply. The FCBC is designed to
operate from AC mains of 150V to 300V. Below 150
and above 300V, the unit gets automatically changed to
battery mode after cutting off the mains supply for AC
operation mode. In case of non-availability of AC mains
and complete discharge of the battery, the entire unit
automatically shuts down to protect it against under
and over voltage variations. This protection is provided
through Relay RL2. FCBC is equipped with a PIC
© 2016, IRJET
Impact Factor value: 4.45
Fig -2: Block diagram of AC/Battery Mode
During the AC operation, the unit gets the supply from
AC input connector. A rectifier, along with a DC-DC
converter enables the required 48V output across pins
of output connector for the operation of ULSB MK-III.
During the operation in AC mode, the unit in addition
to delivering 48V DC to ULSB MK-III, outputs a
charging voltage to the 24V batteries through the
charging circuit comprising a DC-DC converter and a
relay [4].
The block diagram of battery charging mode is as
shown in Fig 3. When the AC mains is ON, the battery
gets charged which functions as a source of load when
AC mains is OFF. When the FCBC is operating in AC
mode, in addition to delivering a DC supply of 48V for
the operation of ULSB MK-III, a DC supply required for
the charging the battery is also generated. This
charging voltage varies from 18 volts to 28 volts
approximately depending on the charge already
available in the battery. The maximum current drawn
by the battery from the charging circuit is about 6
ISO 9001:2008 Certified Journal
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International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 03 Issue: 07 | July-2016
p-ISSN: 2395-0072
PCB 3 (24-48)V DC-DC Converter:
This DC-DC converter works in battery mode when
mains are OFF. The input is 24V DC and the output is
48V DC and is delivered to load
PCB 4 (300-28)V DC-DC Converter:
The input is 24V DC and the output is 48V DC and is
delivered to load.
The rectified 300V DC output voltage is given as input
to the PCB4 to convert to 28V DC to charge the battery
in AC mode.
Depending on the condition of battery, this voltage is
controlled by the trim voltage from the DAC
PCB 5 (AC EMI Filter):
The main purpose of AC EMI filter is to filter the
harmonics and ripple in the circuit.
Fig -3: Block diagram of Battery charging Mode
The hardware implementation of FCBC is as shown in
Fig 5. The parameters that are to be measured on FCBC
is Efficiency.
Efficiency is defined as the ratio of output power to the
input power. The formula of efficiency is shown in
Equation 1.
The PCB layout of entire setup is as shown in Fig 4.
…………… (1)
AC Mode:
DC Mode:
……………. (2)
…………………………………. (3)
………………………………..… (4)
………………………..……………. (5) [4]
Fig -4: PCB Layout of FCBC
PCB 1 (AC-DC Rectifier):
The main purpose of PCB 1 is to convert the 300V AC to
300V DC via a bridge rectifier and is supplied to the
converters for delivering load to the output.
The sensor INA271A measures the voltage drop and
senses the current within the limits.
The PIC16F877A Controller controls the functions of all
IC’s such as UV, OV, Trim voltage, etc…
The DAC MCP4921 delivers the trim voltage to PCB 4
depending on the battery condition.
The regulator 7805 is used to obtain a constant voltage
of 5V to supply power to IC’s.
PCB 2 (300-48)V DC-DC Converter:
The input to the converter is 300V DC and the output
from the converter is 48V DC and is delivered to the
output load.
© 2016, IRJET
Impact Factor value: 4.45
Fig -5: Hardware implementation of FCBC
ISO 9001:2008 Certified Journal
Page 1538
International Research Journal of Engineering and Technology (IRJET)
e-ISSN: 2395 -0056
Volume: 03 Issue: 07 | July-2016
p-ISSN: 2395-0072
Authors are grateful to the Management, BMS
Educational Trust, Principal and Vice-Prinicipal, BMS
College of Engineering for their valuable support.
Authors are thankful to TEQIP-BMSCE, for the extended
Authors also acknowledge Ponginan. S, Ramadas T.K,
Dharneesh, S. Kavya for helping and guiding in solving
the technical issues of this project.
Efficiency for AC and Battery mode operation is
calculated using the following specifications as per
a) Input voltage:
=230V AC
b) Input current:
c) Output voltage:
d) Output current:
e) Battery voltage:
f) Battery current:
= 2.5Amps
= 47.85V DC
= 3.9Amps
= 24V DC
= 5Amps
Efficiency in AC mode:
= (47.85*3.9) + (24*5)
=306.615 W
= 230*2.5*0.7
= 402.5 W
= 76.177% (> 65%)
Efficiency in Battery mode:
= (47.85*3.9)
= 189.36 W
E.Ralph Locher, “Introduction to power supplies”,
National Semiconductor, Application Note A-556,
November 1988.
Global power solutions, “Power supply technical guide”,
technical guide, issue 2, pulication 2007.
Alpha design technologies pvt.ltd, “Technical manual on
FCBC”, technical manual,publication 2014.
Michele sclocchi, “ Input filter design for switching
power supplies”, Application note, literature
E.Mitchel schultz, “ grob’s basic electronics”, text book,
10th edition, A Tata mcgraw- hill publishing company
limited, publication 2007.
circuits,devices and applications”, 3rd edition,
publication 2014.
= (230*2.5)
= 216 W
= 87.66 % (> 75 %)
The efficiency in AC mode is less compared to DC mode
as the AC mode has more ripple compared to DC
(Battery) mode.
Regulated power output is a very important criteria to
be considered in military applications for its
continuous operation. The use of FCBC in ULSB MK-III
resulted in better efficiency. The hardware
implementation and practical testing of FCBC is
discussed and the results obtained are within the
specification limits and satisfactory.
© 2016, IRJET
Impact Factor value: 4.45
ISO 9001:2008 Certified Journal
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