Comparision of Voltage Stress Across The MOSFET Switch of A Flyback Converter With Various Snubbers

Volume 5, Issue 6, June – 2020 International Journal of Innovative Science and Research Technology
ISSN No:-2456-2165
Comparision of Voltage Stress Across the MOSFET

Switch of a Flyback Converter with Various Snubbers
Soumya A.N Nagashree R.S Geetha
Dept. of EEE Dept. of EEE Dept. of EEE
BMSCE BMSCE BMSCE
Bengaluru, India Bengaluru, India Bengaluru, India
Abstract:- A Flyback converter is a simple switch-mode The main focus in this paper is to compare voltage
power supply that can be used to generate a DC output stress on the converter switch using different snubber
from either an AC or DC input. The converter switch is circuits. This paper is organized as follows: Section I
the most critical part of any converter. The voltage consists of an introduction, Section Ⅱ explains the working
stress across the switch is a major issue as the high
voltage spikes occur due to interaction between its of Flyback converter, Section Ⅲ discusses about various
output capacitance and the leakage inductance of the types of snubber and its working, Section Ⅳ discusses the
transformer. These spikes can be reduced with various
simulation results of the Flyback converter with various
snubbers like conventional tertiary winding, Resistor
types of snubbers.
Capacitor and Diode(RCD) snubber, energy
regenerative snubber and an active clamp snubber. This
II. FLYBACK CONVERTER
paper aims to analyze and compare the voltage stress
across the MOSFET switch of Flyback converter with
Flyback converter is the most popular DC-DC
various snubber circuits.
converter topology for the applications involving 150W of
power or less as it is simple and cost effective. The basic
Keywords:- Active clamp snubber; Energy regenerative
topology of a Flyback circuit is shown in Fig. 1.
snubber; Flyback converter; RCD snubber; Tertiary
winding reset.
I. INTRODUCTION
Flyback converter is the simplest isolated DC-DC

converter topology widely used in low power applications
due to its cost effectiveness and electrical isolation
characteristics [1]. Its main power circuit comprises of a
MOSFET as a switch, a transformer, an output diode and Fig 1:- Conventional Flyback converter [2]
an output filter capacitor. The transformer winding
polarities of flyback converter are designed in such a way During switch on condition the energy is incorporated
that when the current passes through only one winding at a into the primary winding and due to the dot convention of
time [1]. the transformer as shown in Fig. 1, the energy from the
secondary winding does not get supplied to the load [3].
The application of transformer is an efficient method During this period, the output capacitor supplies the energy
to provide the electrical isolation between input and output to the load. During turn OFF condition, no current flows in
of a dc-dc converter [1]. A steady current builds-up in the transformer’s primary. Simultaneously, the
every cycle, within the magnetizing inductance of the transformer’s secondary voltage polarity changes.
transformer. This steady buildup of current results in Therefore, the energy is carried from the transformer to the
saturation of the transformer core [1]. Therefore, it needs to output. Thus, the operation of converter is determined by
be reset always for each pulse and this problem can be the dot-ends of the inductor [3]. The amount of output DC
solved by using a tertiary winding [1]. In Flyback voltage depends on the on-time of the switch during a
converters, switching voltage spikes appears across the switching period. For longer on time of the switch, larger
converter switches during its turn off time that can be output DC voltage is obtained. The transformer must be
reduced with the addition of snubber circuit [1]. A snubber reset to equalize the negative volt-seconds and positive
normally comprises of a capacitor that is greater than the volt-seconds. If this condition is not satisfied, then a large
output capacitance of the switch that helps to discharge the amount of energy will be stored in the transformer during a
output capacitor. A snubber circuit also serves to reduce switching cycle [3]. Due to this, the net accumulation of
turn-off switching losses [1]. energy causes the transformer saturation and also leads to
the short circuit of primary resulting in the failure of the
switch.
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ISSN No:-2456-2165
III. VARIOUS TYPES OF SNUBBERS A Flyback converter with energy regenerative snubber
is shown in Fig.3.
A. Tertiary winding method
The tertiary winding method is commonly used as
“reset” winding. This reset winding is tightly coupled to the
primary winding, to minimize the leakage between the
primary winding and the reset winding. This reset winding
can take-up all the ampere-turns from the primary winding
when the switch turns OFF [3].
B. Resistor Capacitor and Diode(RCD) snubber

Resistor Discharge Clamp(RCD) is one of the
simplest snubber circuit consisting of a resistor, a capacitor
and a diode. The problem of voltage stress can be solved
by the traditional method called passive RCD [4]. The
flyback converter with RCD snubber circuit is shown in Fig 3:- Flyback converter with energy regenerative snubber
Fig.2. [7].
(1)
(2)
Where,
: Input voltage;
: Magnetizing inductance;
: Leakage inductance;
: Current through the magnetizing inductance at time t;
: Current through the leakage inductance at time t.
D. Active clamp snubber

An active clamp snubber is the one that consists of an
active switch as shown in Fig. 4.
Fig 2:- Flyback converter with RCD snubber [5]
The flyback converter with the RCD snubber works as

follows: During turn off, the transformer leakage current has
two ways, the first one can be through the output
capacitance of the switch and one more through the snubber
circuit clamp capacitor (Csn).
In Flyback converter with RCD snubber, the rate of

rise of voltage across the switch is slower since the net
capacitance is larger resulting in lesser voltage across the
switch [5].
C. Energy regenerative snubber Fig. 4:- Flyback converter with active clamp snubber [8]
The most efficient snubbers are the ones that has an
ability to regenerate the energy without dissipating it [6]. An auxiliary switch and a clamp capacitor are used to
The converter works as follows: During the turn off reduce the voltage stress of active switch in the flyback
condition of switch Smain, the energy to the snubber converter [9]. This active switch enables the snubber to
capacitor Cclamp is supplied from the leakage inductance work with zero-voltage switching (ZVS). Application of
through the diode D1. Gradually, the current through D1 ZVS assures a vital reduction of switching losses due to the
and Cclamp decreased to zero. During the turn-on period of non-overlapping of voltage and current [10].
the switch, Cclamp discharges through the path that
includes a switch, the diode Dreg, and the auxiliary The flyback converter with active clamp snubber
winding. As the auxiliary winding(Lm)is linked to the main works as explained below: While the main switch S1 is
transformer thus the energy in the Cclamp is accumulated made to turn off, the energy of the transformer leakage
in the transformer [6]. This stored energy is discharged to inductance Lr is carried to the snubber capacitor Cclamp by
the output in addition to the energy that is usually stored in the body diode of S2[10When the current flows through its
the flyback transformer during turn off condition [6]. body diode, S2 can be turned on with ZVS [10]. In the

ISSN No:-2456-2165
following switching cycle, the S1 is turned on and S2 is Fig. 6 shows the voltage stress across the switch with
turned off, then the current begins to flow through the body tertiary winding method.
diode of S1, thus enabling switch S2 to turn on with ZVS.
IV. SIMULATION RESULTS
Flyback converter with various snubbers are simulated

using LTspice tool. The voltage stress across the MOSFET
with different snubber circuits are compared and the results
are discussed as below.
The designed values of Flyback converter are shown in

Table 1:
Input voltage 24V

Output voltage 7V Fig 6:- Voltage stress across the switch with tertiary
Duty ratio 40% winding
Output power 10watt
It is observed that, with an input voltage of 24V, the
Efficiency ≥75% voltage stress across the switch is 480V.
Turns ratio 3.0
Switching frequency 40kHz  RCD snubber
Primary winding inductance 90uH
Secondary winding inductance 10uH
Output Capacitance 200uF
Load 8 ohm
Table 1:- Designed Values of the Flyback Converter
Fig.5 to Fig.12 presents the voltage stress across

MOSFET of Flyback converter with tertiary winding, RCD
snubber, energy regenerative snubber and active clamp
snubber.
 Tertiary winding method
Fig 7:- Flyback converter with RCD snubber
Fig. 8 shows the voltage stress across the switch with a

RCD snubber.
Fig 8:- Voltage stress across the switch with RCD snubber
Fig 5:- Flyback converter with tertiary winding
It is observed that, with an input voltage of 24V, the
voltage stress across the switch is 450V.

ISSN No:-2456-2165
 Energy regenerative snubber Fig. 12 shows the voltage stress across the switch with
a active clamp snubber
Fig 12:- Voltage stress across the switch with active clamp
snubber.
Fig 9:- Flyback converter with energy regenerative
snubber It is observed that, with the input voltage of 24V, the
voltage stress across the switch is 54V.
Fig. 10 shows the voltage stress across the switch with
a energy regenerative snubber. The input and output voltage for the Flyback
converter with all the snubbers are common as specified in
Table 1 and the same is shown in Fig.13.
Fig 10:- Voltage stress across the switch with energy

regenerative snubber.
It is observed that, with the input voltage of 24V, the Fig 13:- Input and output voltage of Flyback converter
voltage stress across the switch is 180V. with various snubber circuits.
 Active clamp snubber It is observed that, with the input voltage of 24V, the
output voltage with all the snubbers is observed to be
constant at 7V.
The input voltage, output voltage and voltage stress

across the switch with all snubbers are summarized in
Table 2.
Table 2:- Comparision of Voltage Stress with All Types of

Fig 11:- Flyback converter with active clamp snubber
Snubbers

ISSN No:-2456-2165
It is observed from Table 2 that the voltage stress [8]. S. M. Tadvin, S. R. B. Shah and M. R. T. Hossain.
across the switch of a Flyback converter with active clamp (2018) "A Brief Review of Snubber Circuits for
snubber is less when compared with other types of snubbers. Flyback Converter,"3rd International Conference for
Convergence in Technology , (pp.1-5).
V. CONCLUSION [9]. Bor-Ren Lin, Kevin Huang and David Wang. (2006)
"Analysis, design, and implementation of an active
In this work, the simulation results with different clamp forward converter with synchronous rectifier,"
snubber circuits namely Tertiary winding method, RCD in IEEE Transactions on Circuits and Systems vol. 53,
snubber, Energy regenerative snubber and Active clamp no. 6,( pp. 1310-1319).
snubber are discussed for a Flyback converter. [10]. Y. Liu, B. Huang, C. Lin, K. A. Kim and H. Chiu.
(2018) "Design and Implementation of a High Power
The voltage stress across the MOSFET switch of the Density Active-Clamped Flyback Converter,"
Flyback converter is compared with these different snubber International Power Electronics Conference ( pp.
circuits. It is observed from the simulation results that, 2092-2096).
active clamp snubber is found to be better compared with all
other snubbers circuits considered in this work as the
voltage stress across the MOSFET switch is found to be the
least.
ACKNOWLEDGEMENT
Authors are grateful to the management, BMS

Educational Trust, Principal and Vice-Principal, BMS
college of Engineering for their valuable support.
REFERENCES
[1]. Daniel. W. Hart, “Power Electronics”, The McGraw-

Hill Company, 3rd edition, 2010.
[2]. A. Boyar and E. Kabalci. (2018) "Comparison of a
Two-Phase Interleaved Boost Converter and Flyback
Converter," IEEE 18th International Power
Electronics and Motion Control Conference, (pp. 352-
356).
[3]. N. Coruh, S. Urgun and T. Erfidan. (2010) "Design
and implementation of flyback converters," 5th IEEE
Conference on Industrial Electronics and
Applications, (pp. 1189-1193).
[4]. H. Chung, S. Y. R. Hui and W. H. Wang. (1997) "An
isolated fully soft-switched flyback converter with
low voltage stress," PESC97. Record 28th Annual
IEEE Power Electronics Specialists Conference.
Formerly Power Conditioning Specialists Conference
1970-71. Power Processing and Electronic Specialists
Conference , (pp. 1417-1423 vol.2)
[5]. R. Kanthimathi and J. Kamala. (2015) "Analysis of
different flyback Converter topologies," International
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[6]. C. Liao, and K. Smedley. (2008) “Design of High
Efficiency Flyback converter with energy regenerative
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Comparision of Voltage Stress Across The MOSFET Switch of A Flyback Converter With Various Snubbers

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Volume 5, Issue 6, June – 2020 International Journal of Innovative Science and Research Technology

Comparision of Voltage Stress Across the MOSFET

Flyback converter is the simplest isolated DC-DC

IJISRT20JUN1114 www.ijisrt.com 1567

B. Resistor Capacitor and Diode(RCD) snubber

D. Active clamp snubber

The flyback converter with the RCD snubber works as

In Flyback converter with RCD snubber, the rate of

IJISRT20JUN1114 www.ijisrt.com 1568

IV. SIMULATION RESULTS

Flyback converter with various snubbers are simulated

The designed values of Flyback converter are shown in

Input voltage 24V

Fig.5 to Fig.12 presents the voltage stress across

 Tertiary winding method

Fig 7:- Flyback converter with RCD snubber

Fig. 8 shows the voltage stress across the switch with a

IJISRT20JUN1114 www.ijisrt.com 1569

Fig 10:- Voltage stress across the switch with energy

The input voltage, output voltage and voltage stress

Table 2:- Comparision of Voltage Stress with All Types of

IJISRT20JUN1114 www.ijisrt.com 1570

Authors are grateful to the management, BMS

[1]. Daniel. W. Hart, “Power Electronics”, The McGraw-

IJISRT20JUN1114 www.ijisrt.com 1571

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