Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349 –2252, ISSN (Print):2349 –2260
Volume 2 Issue 5 May 2015
DESIGN AND IMPLEMENTATION OF MULTI OUTPUT ZVS
FLYBACK CONVERTER
K. Anitha1, S. Grace shalini2
1
PG Scholar, Department of Electrical and Electronics Engineering,
Dhanalakshmi Srinivasan College of Engineering and Technology, Chennai.
2
Associate professor, Department of Electrical and Electronics Engineering,
Dhanalakshmi Srinivasan College of Engineering and Technology, Chennai.
Abstract— In this paper a new multi output ZVS flyback converter is proposed. The primary side of a
isolation transformer has a half-bridge inverter and the secondary side of a isolation transformer has a
flyback rectifier integrated with auxiliary buck converter. The synchronous switches are used to control
the output voltages. Magnetizing offset current are maintained at lower range, it leads to the transformer
size get reduced as well as it has no cross regulation problem. The proposed converter can achieve the
lower output voltage because it has wide turn on period. In this work flyback converter are analyzed,
mathematical modeled and designed with given parameters. A 24 V/7 A and 12 V/2 A and 6 V/0.7 A
hardware is built and tested to verify the simulation results and the voltage regulations of the multi
outputs of the proposed converter.
Index Terms— Buck, flyback, multioutput, synchronous switch, Zero Voltage Switching (ZVS).
I.INTRODUCTION
Multioutput DC/DC converters are widely used
in Switch Mode Power Supplies (SMPS) due to
their competitive cost and size [1]. The proposed
converter is based on the half-bridge fly back
converter for the main output and the buck
converter for the auxiliary outputs. The buck
converter is integrated with the secondary
flyback rectifier. This integration makes simple
structure and low transformer size and ZVS of
all the switches are achieved. Cross regulation
problems among the outputs do not occur [2].
Flyback converters are popular topologies
widely used in isolated dc-dc power converters
to meet the following purposes (a) Isolation
between the source and load; (b) Reduction of
size and weight;(c) Controlled direction of
power flow;(d) High conversion efficiency (e)
Input and output Voltage waveform with a low
Total Harmonic Distortion;(f) Controlled power
factor if the source is an ac supply [3]. These
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topologies are followed by designers for their
simplicity, ability to handle multiple isolated
outputs[4].
Flyback converters are widely applied on
electrical power supply circuits with low power
demand. It has high efficiency & low cost. The
transformer in the flyback converter is used to
isolate the electric signal and store the magnetic
energy. The limited power handling capability is
imputed to this converter’s buck-boost based
behavior[5].Power Switch in the flyback
converter has voltage and current stress due to
resonance between leakage inductance of
transformer and channel capacitor of switch.
Therefore an auxiliary circuit is necessary to
absorb the voltage spike and provide soft
Switching
condition
for
semiconductor
devices[6].To realize high switching frequency
and high efficiency at the same time the soft
switching technology is introduced, which aims
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Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349 –2252, ISSN (Print):2349 –2260
to reduce the switching power loss by turning
on/off the switch when the voltage across it
and/or the current through is zero at the
switching instant[7]. ZVS turn-on of the
synchronous switches will reduce the voltage
stress and solve the reverse recovery problem of
the body diode of synchronous switches.ZVS
eliminates the capacitive turn on loss. It is
suitable for high frequency operation[8][9][10].
II.OPERATION AND DESIGN OF
MULTIOUTPUT ZVS FLYBACK
CONVERTER
A.Operation of multioutput ZVS flyback
converter
Fig 1 Circuit diagram of the conventional halfbridge flyback Converter with auxiliary buck
converter
Fig 2 Circuit diagram of the integration of the
secondary switches
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Volume 2 Issue 5 May 2015
Fig 3 Circuit diagram of the proposed
multioutput ZVS flyback converter with three
switches.
Fig.1 shows the conventional half bridge flyback
converter and auxiliary buck converter. An
active snubber is used in the proposed converter
to protect the main and auxiliary switches from
voltage and current stresses. Both main and
auxiliary switches are turned on at Zero Voltage
Switching(ZVS) using asymmetrical gate
control. From the main output we can derive the
auxiliary outputs using Buck converter.
MOSFET is used as a switch in this converter
because it is a fast switching device and it is
suitable for high frequency operation .When the
switch is turned on energy is stored from
primary magnetising inductance to secondary
magnetizing inductance to output of load.
Similarly when switch is turned off energy
stored from primary magnetizing inductance
does not flow to secondary magnetizing
inductance. Fig.2. shows the derivation of
proposed secondary side. The switches of the
the buck converter are integrated with the
flyback converter switches and it is divided in
to two synchronous switches QS1 and QS2. The
two synchronous switches QS1 and QS2 will
provide the current path for the main output.
The powering and freewheeling path for
auxiliary output is provided by QS2 and QS1
respectively [2].
Fig.3 shows the circuit configuration of the
proposed multioutput ZVS flyback converter
with three switches. It consists of a half bridge
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Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349 –2252, ISSN (Print):2349 –2260
inverter from Fig.1 and derived secondary
rectifier from Fig. 2
Volume 2 Issue 5 May 2015
Ripple factor(r):
IAC/IDC = 0.02%
The primary side of a transformer has the main
switch QM is operated in a duty ratio of D, and
the auxiliary switch QA is operated
complementary to the main switch QM. The
secondary switches QS2, QS3 is turned on
simultaneously with QA and QS1 is turned on
after QS2, QS3 is turned off. Both main and
auxiliary outputs are controlled by controlling
the duty ratio of D and DS, where D is the duty
ratio of the main switch QM,and DS is the duty
ratio of the overlap interval of QM and QS2, QS3.
By adding L and C to the synchronous buck
converter we can achieve Zero Voltage
Switching(ZVS). The auxiliary switch is used to
control the off time of the switching period.
To create a resonance an active snubber
circuit including clamp capacitor and resonant
inductor is used in the circuit so that the
switches can be turned on at ZVS.
 All parasitic components are neglected
 The parasitic capacitances Coss1 and Coss2
are the same capacitances of Coss.
 The output voltages V01,V02 ,V03 and the
blocking capacitor voltages VCB are constant
during the switching cycle.
 The transformer turns ratio n = Np/ NS.
E1 = 4.44 N1 φ f = 48=4.44* N1*20*10^6*10*10^3
(1)
N1=50
E2 = 4.44 N2 φ f = 12=4.44* N2*20*10^6*10*10^3
(2)
N2=12
Inductor selection:
F=
√ √
(3)
L =4µH
Output capacitor selection:
C=
(4)
√
C= 720 µF
C. Simulation results
The simulated waveforms of output voltage of
multioutput ZVS flyback converter for Vin
=48V,Iin=12A.
B.Design of multioutput ZVS flyback
converter
The multioutput ZVS flyback converter is
designed in this work.
Input voltage Vin
= 48V
Output voltage VO = 24V,12V,6V.
Switching frequency = 50KHZ
F
= 10KHZ
RL = 1KΩ
Fig 4 Simulation waveforms of input voltage Vin
=48V,Iin = 12A
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33
Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349 –2252, ISSN (Print):2349 –2260
Volume 2 Issue 5 May 2015
III.MODES OF OPERATION FOR
MULTIOUTPUT ZVS FLYBACK
CONVERTER
Fig 5 Simulation waveforms of output voltage
VO1=24V
Based on the on/off states of the switches the
proposed multioutput ZVS flyback converter has
six operating modes. The main switch QM is
turned on and turned off alternatively with a
duty ratio of D, at constant frequency and the
auxiliary switch QA is turned on and turned off
complementary to the main switch QM. Both the
secondary switches QS2, QS3 and the auxiliary
switch QA are turned on simultaneously and QS1
is turned on after QS2, QS3 is turned off. Duty
ratios D and DS controlling the main and
auxiliary output respectively, where D is the
duty ratio of the main switch QM and DS is the
duty ratio of the overlap interval of QM and QS2,
QS3[2].
Fig 6 Simulation waveforms of output voltage
VO2=12 V
(a) Mode 1
Fig 7 Simulation waveforms of output voltage
VO3=6 V
(b) Mode 2
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34
Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349 –2252, ISSN (Print):2349 –2260
(c) Mode 3
(d) Mode 4
Volume 2 Issue 5 May 2015
Mode 1[t0-t1]: At t0, the main switch QM and
the secondary switch QS1 are turned on with
ZVS. The leakage current ilkg(t) reaches iLm(t)+
iLO1(t)/n in this mode. The supply for the primary
side of the transformer is the difference between
the input voltage and the voltage across the
capacitor, VS-VCB. The magnetizing inductance
is linearly charged [8]. So that the magnetizing
current iLm(t) is linearly increased. The output
inductor current iLO1(t) flows through the
secondary switch QS2. ilkg(t), iLm(t) and iLO1(t) can
be expressed as follows:
ilkg(t) = iLm(t) + iLO1(t)/n
(5)
iLm(t)=
(6)
(t-to)+iLm(to)
iLO1(t) = -iS2(t)
(7)
Mode 2[t1-t2]: At time t1 the secondary switch
QS2, QS3 is turned off. In this mode the output
inductor current iLO1(t) flows through QS1.
Therefore, the auxiliary output is in free
wheeling mode. ilkg(t), iLm(t) and iLO1(t) can be
expressed as follows:
(e) Mode 5
ilkg(t)= iLm(t)=
iLO1(t)= iS1(t)=
(f ) Mode 6
Fig 8 Operational modes of the proposed
converter.
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(t-t1)+iLm(t1)
(t-t1)+iLO1(t1)
(8)
(9)
Mode 3[t2-t3]: At t2, the main switch QM is
turned off. In this mode the leakage current ilkg(t)
are assumed to be at constant and it is charging
and discharging the capacitances COSS1and COSS2
linearly. The secondary switch voltage of QS2 is
also get decreased. The ZVS of the auxiliary
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Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349 –2252, ISSN (Print):2349 –2260
switch QA and the secondary QS2 can be achieved
at VP= -VCB. ilkg(t), iLm(t) and iLO1(t) can be
expressed as follows:
ilkg(t) = iLm(t) + iLm(t2)
(10)
iLO1(t) =
(11)
(t-t2)+iLO1(t2)
Mode 4[t3-t4]: In this mode, the auxiliary
switch QA and secondary switch QS2 is turned on
with ZVS condition. The main output VO2 will
get power from the primary side. The difference
between the voltage obtained from the
secondary side, nVO2 and the blocking capacitor
voltage, VCB is equal to the leakage inductance
voltage. The secondary transformer current is
n(iLm(t)− ilkg(t)). In this mode also the auxiliary
output is in freewheeling mode. The current
flowing through secondary switch QS1 is the
sum of iLO1(t) and the switch QS2 current iS2(t).
ilkg(t), iLm(t) and iLO1(t) and the secondary switch
current iS2(t) and iS1(t) can be expressed as
follows:
(
ilkg(t) =
)
( )
Volume 2 Issue 5 May 2015
iS1(t) =iS2(t) +iLO1(t)
(16)
Mode 5[t4-t5]: Auxiliary switch QA is turned off.
The parasitic capacitances
COSS1 and COSS2
resonates with leakage inductance Llkg. The
leakage inductor current ilkg (t) discharge and
charge the capacitances COSS1 and COSS2
respectively.The secondary switch QS2 is still on
state. ilkg (t), iLm (t),and iLO1(t) can be expressed
as follows:
ilkg(t) =
iLm(t) =
(
)
( )
(17)
( )
(18)
( )
iLO1(t) =
(19)
(12)
Mode 6[t5-t6]: Mode 6 begins when QM is
turned on with ZVS. (VS -VCB)+
is applied
to the leakage inductance, so the leakage current
ilkg (t) is rapidly increased. When ilkg (t) reaches
to iLm(t)+ iLO1(t)/n ,this mode ends. ilkg (t), iLm
(t),and iLO1(t) can be expressed as follows:
(
)
( )
iLm(t) =
(t-t3) + iLm(t3)
(13)
ilkg(t) =
iLO1(t) =
(t-t3) + iLO1 (t3)
(14)
iLm(t) =
(
)
( )
(15)
iLO1(t) =
(
)
( )
iS2(t) =n( iLm(t) – ilkg(t))
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(20)
(21)
(22)
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Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349 –2252, ISSN (Print):2349 –2260
Volume 2 Issue 5 May 2015
IV. EXPERIMENTAL RESULTS
In this section a hardware prototype is built and
tested to verify the analysis results and to
demonstrate the voltage regulation of the three
output voltages in the proposed converter. The
design circuit parameters are listed in the table.
Table 1 Circuit Parameter
Component
value
Main Switch
IRF840
Auxiliary switch
IRF840
Output inductor
4µH
Output capacitor
720 µF
Diode
IN4007
Fig 10 output voltage waveform VO1=24V
Fig 11 output voltage waveform VO2=12V
Fig 9 input voltage waveform Vin =48V,Iin =
12A
Fig 12 output voltage waveform VO3 = 6V
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37
Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349 –2252, ISSN (Print):2349 –2260
V. TOPOLOGICAL EXTENSION
Fig 13 N multiple outputs
In the proposed multioutput ZVS flyback
converter there are three secondary switches
and three outputs. However the number of
switches is not limited, we can increase the
number of switches to produce the larger
number of outputs as shown in fig.13. The
output voltages are regulated by the duty
ratios.
VI. RESULT ANALYSIS
VII. CONCLUSION
A detailed analysis of multioutput ZVS flyback
converter is discussed. The basic concept of
flyback converter is figured out. Different modes
of multioutput ZVS flyback converter along
with the necessary circuit diagram and
waveforms have been discussed. The operational
principle, analysis, and design considerations are
illustrated in this paper. The validity of the basic
operational principle is verified by the
Experimental results with 24V/7A and 12V/2A,
6V/0.7A prototype, which allow us to draw the
following conclusions:
1) Auxiliary buck converter makes simple
structure;
2) The powering period of the auxiliary and
main output are separated each other during DTS
and (1-D) Ts, respectively. So that the
transformer offset current is reduced;
3) ZVS is achieved for all the switches by gate
control, without additional component;
4) Cross regulation problems are avoided.
efficiency(%)
REFERENCES
Measured
[1] Byeong-Cheol Hyeon,Bo-Hyun cho, ―A
tightly regulated triple output Asymmetrical
Half-bridge Flyback converter ,‖Journal of
Power Electronics Vol.10,No.1,January
2010.
Load(%)
Fig 14 Comparison of Efficiency under load
variations.
Thus the Fig.14 shows the wave forms of the
efficiency improvement of the proposed
converter. The efficiency of the proposed
converter increased accordingly with load.
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Volume 2 Issue 5 May 2015
[2] Jae-Kuk Kim, Jae-Bum Lee and Gun-Woo
Moo, ―Zero-Voltage Switching Multioutput
Flyback
Converter With Integrated
Auxiliary Buck Converter,‖ IEEE Trans.
Power Electron., vol. 29, no. 6,june 2014.
[3] Aruna N.S, Dr.S.G. Srivani, Balaji p,
―Multi Output Active Clamped Flyback
Converter,’’International
Journal
of
Advanced Research in Electrical and
Electronics Instrumentation Engineering
(IJAREEIE ) Vol.3, Issue 7 July 2014.
38
Journal of Recent Research in Engineering and Technology
ISSN (Online): 2349 –2252, ISSN (Print):2349 –2260
Volume 2 Issue 5 May 2015
[4] Marn-Go kim and Young-Seok jung ―A
Novel Soft Switching Two Switch flyback
converter with a wide operating range and
Regenerative Clamping,‖ Journal of power
Electronics,Vol.9,No.5, September 2009.
[5] DR. R. Seyezhai, K. Karthika, S. Dipika
Shree, MadhuVanthani
Rajendran ,
―Design and Simulation of a Soft Switched
interleaved flyback converter for a fuel
cell,‖IJMIE volume 2 issue 9.
[6] Majid Delshad,Abbas Narimani ―A new Soft
Switching Flyback Dc-Dc converter with
Minimal Auxiliary circuit Elements,‖
Universal Journal of Electrical and
Electronics Engineering 1(4):105-109,2013.
[7] Xinyu Xu, Ashwin M. Khambadkone,
Ramesh Oruganti ―An Asymmetrical Halfbridge Flyback converter with Zero Voltage
and Zero Current Switching,‖ 30th Annual
Conference of the IEEE industrial
Electronics Society November 2-6,2004,
Busan,Korea.
[8] Hyun-Lark Do, ―Zero Voltage Switching
Synchronous Buck Converter with
a
Coupled Inductor,‖ IEEE Transactions on
industrial electronics, Vol.58,No.8, August
2011.
[9] B. Nagaraju, K. Sree Devi, ―A Novel active
clamped Dual Switch Flyback Converter,‖
International journal of Engineering
Research and Applications(IJERA)Vol.2,
issue 1, Jan-Feb 2012,PP.195-206.
[10] T. Halder, ―Improved Performance Analysis
of Clamp Circuits with Flyback Converter,‖
International
Journal
of
Emerging
Technology & Advanced Engineering
ISSN:
2250-2459,
Volume
2,Issue
1,January 2012.
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