International Journal of Research and Engineering
Volume 3, Issue 1
Step Down Converter With Efficient ZVS Operation
Author: Akhila Ramachandran S
PG Scholar, Dept. of EEE, Toc H Institute of Science & Technology Arakkunnam P.O, Kerala, India
Toc H Institute of Science & Technology Arakkunnam P.O, Kerala, India
akhilaramachandran92@gmail.com
Abstract— Step down converters has many applications in
modern electronic devices. For these purposes, circuits
have voltage/current requirements outside the efficient
range of most classical converters. Therefore there was an
urge for development of new converter topologies.
Converters employing soft switching methods were
emerged as an efficient alternative while considering the
switching losses of a conventional converter. Here
modifications are made on conventional buck converter.
An auxiliary switch, a diode, and a coupled winding to the
buck inductor are added with the conventional buck
converter. By transferring the buck inductor current to the
coupled winding in a very short period, a negative built-up
of leakage inductor current in buck winding is achieved,
which guarantees the Zero- Voltage Switching (ZVS)
operation of the buck switch in all load conditions.
Furthermore, since the negatively built-up leakage
inductor current is minimized after the zero voltage of the
buck switch is achieved; the unnecessary current build-up
and the conduction loss are minimized. Therefore, a
converter with efficient ZVS operation with load variation
is achieved. To verify the performance of this topology,
simulations are done using MATLAB or SIMULINK.
resonant tank can be used in converters with Synchronous
Rectifiers (SR) to achieve the ZVS of the power switch [3]. In
low output voltage dc-dc converters, SRs are widely utilized to
reduce rectifier conduction loss and improve converter
efficiency. By the introduction of active resonant tank even
though it eliminate reverse recovery of the body diode, this
converter induces conduction loss in the added inductor and
capacitor
In [4] and [5] an auxiliary circuit is utilized to obtain zero
voltage and zero current switching in zero voltage transition
PWM converters. They provide zero-current switching during
turn-on and zero-voltage switching during turn-off. The
switches do not experience any over voltage/over current stress
proportional to load as in resonant converters. The major
disadvantage is that the active switches in the converter
undergo zero-capacitive turn-on losses.
A simple ZVS buck converter with a coupled inductor is
presented in [6] and [7] with small additional components.
However, a large current is built up in the coupled winding in
light-load conditions and therefore greatly increases
conduction loss. In addition, less power is transferred to the
output during the switch-off period, which increases the dc
value of the buck- inductor current.
Keywords—DC DC converters; buck converter; Zero
Voltage Switching;
I. INTRODUCTION
Rapid technological changes have led to power electronic
products playing a crucial role in daily life. Solar power
regulators, LED, drivers and portable electronic equipment,
such as laptop computers, cellular phones, and future
microprocessors and memory chips, requires step down
converters for their operation. Buck type dc - dc converters
are widely employed for step down operation in the power
electronics industry because no other topology is as simple.
Their applications range from low-power regulators to very
high power step - down converters, which are characterized by
a low number of components, low control complexity, and no
insulation.
For above mentioned applications, high power density,
high efficiency, and low noise are the driving force in power
converter research. High power density can be achieved by
increasing switching frequency since magnetic and capacitive
elements can be designed in small sizes in high frequencies but
it increases switching loss and degradation of system
efficiency. Soft-switching techniques can alleviate switching
losses, and thus, they allow for higher frequency operation,
higher efficiency, low harmonic level, and high power density.
The choice of the soft-switching technique depends on the type
of switching device, and the ZVS technique is more preferable
in MOSFET switches since it eliminates the capacitive loss of
a power switch during the turn-on transition.
Various types of ZVS techniques are presented in [1]-[7]. An
efficiency improved version of Synchronous buck converter
with passive auxiliary circuit is presented in [2]. This converter
well utilized the parasitic components of the power switch
with additional resonant components. However, higher voltage
and current stresses are common in this converter. The active
II. NEW ZVS TOPOLOGY
The new step-down ZVS converter composed of an
auxiliary switch, a diode, and a coupled winding in the
conventional buck inductor. The basic operation of the new
converter topology can be explained as follows. During a very
short turn-on period of the auxiliary switch, the buck inductor
current is transferred to the coupled winding and the leakage
inductor current is built up negatively. It makes the output
capacitor of power switch to discharge hence obtaining zero
voltage across the power switch. It guarantees the ZVS of the
switch in all load conditions through the negative leakage
inductor current. Furthermore, since the negatively built-up
leakage inductor current is minimized after the zero voltage of
the buck switch is achieved, the unnecessary current build-up
and conduction loss are minimized as the load goes down,
which indicates the efficient ZVS operation with load
variation.
19
Figure 1. New ZVS Topology
The new step down converter topology is shown in Figure
1 the operating waveforms are shown in Figure 2.
ISSN 2348-7852 (Print) | ISSN 2348-7860 (Online)
(This work is licensed under a Creative Commons Attribution 4.0 International License.)
http://www.ijre.org
International Journal of Research and Engineering
Figure 2. Operational Waveforms
Mode 1 (t0 to t1): At t0 leakage inductor current iLr
reaches the buck-inductor current iLb. Since buck switch Sb is
in the on state, Since n < 1 and Vin > Vo, VSx and VDx are
positive and the output diode of switch Sx and diode Dx
remains in the off state. This mode ends when switch Sb is
turned off.
Mode 2 (t1 to t2): In Mode 2, diode Db is in the on state
and the buck- inductor voltage VLb = -Vo. Since n < 1 and
Vin > Vo, VSx and VDx are positive and the output diode of
switch Sx and diode Dx remain in the off state. This mode ends
when switch Sx is turned on.
Mode 3(t2 to t3): When switch Sx is turned on, the coupled
winding voltage Vx becomes Vin - Vo. Then, the voltage of
leakage inductors VLr is given by
𝑉 − 𝑉0
𝑉𝐿𝑟 = − 𝑖𝑛
(1)
𝑛 + 𝑉0
Since turn ratio 'n' is a little smaller than unity, the leakage
inductor voltage VLr has a large negative value. Then, the
leakage inductor current iLr decreases rapidly down to zero
since leakage inductor Lr has a very small value. The voltage
of diode Dx and switch Sb is Vin during this mode. This mode
ends when the leakage inductor current iLr reaches zero.
Mode 4 (t3 to t4):
Mode 4 has a very short period
compared with Mode 3. After the leakage inductor current iLr
reaches zero, it flows in the negative direction and to the
charge and discharge output capacitors of diode Db and the
output capacitor of switch Sb, respectively, in a resonant
manner, as shown in Figure. 3. The voltage across switch Sb
varies from Vin to zero in this mode. The ZVS of switch Sb is
always achieved only if switch Sx is not turned off before
voltage VSb reaches zero. Since the leakage inductor Lr and
output capacitor Cs have very small values and the time
interval within which switch voltage VSb decreases from Vin
to zero is very short, switch Sx is never turned off before VSb
reaches zero. Therefore, the ZVS of switch Sb is already
guaranteed.
Mode 5 (t4 to t5): Mode 5 begins when VSb reaches zero
voltage. When VSb reaches zero voltage, the output diode of
switch Sb is turned on and maintained in its ON state during
this mode since the voltage of the leakage inductor VLr
remains negative such that the leakage inductor current still
flows in the negative direction. Mode 5 ends when switch Sx is
turned off.
Volume 3, Issue 1
Figure. 3. Operational circuit of each mode: (a) Mode 1 (t0−t1),
(b) Mode 2 (t1−t2) (c) Mode 3 (t2−t3), (d) Mode 4 (t3−t4), (e)
Mode 5 (t4−t3), and (f) Mode 6(t5−t0).
Mode 6 (t5 to t0): As switch Sx is turned off , switch Sb is
turned on with a zero-voltage condition since the output diode
of switch Sb is in the on state. A large positive voltage is
applied to the leakage inductor, the leakage inductor current
iLr increases rapidly up to the buck-inductor current iLb. This
mode ends when the leakage inductor current iLr reaches the
buck-inductor current iLb.
TABLE I
PARAMETERS AND SPECIFICATIONS.
Parameter
Input Voltage
Output Voltage
Output Power
Switching frequency
Coupled
L1
Inductor
L2
n
Capacitor
Cs
Attributes
100 V
50 V
300 W
125 KHz
250.6µH
181.4µH
.85
47µF
III.
SIMULATION RESULTS
The circuit was simulated in MATLAB/SIMULINK. The
open loop simulation of the converter is shown in Figure.3.
Simulation result of output voltage and current is shown in
Figure.4.
Figure 4. Open loop simulation diagram
20
ISSN 2348-7852 (Print) | ISSN 2348-7860 (Online)
(This work is licensed under a Creative Commons Attribution 4.0 International License.)
http://www.ijre.org
International Journal of Research and Engineering
Figure 5 Open loop simulation results
Figure 6. Closed loop simulation diagram
Figure 7. Closed loop simulation results
The closed loop simulation of new step down
converter with ZVS operation is shown in Figure 6. Closed
loop helps to maintain required output voltage and keep it
21
Volume 3, Issue 1
constant when input changes. Simulation result of output
voltage is shown in Figure.7.
IV.
CONCLUSION
A new step down converter topology with efficient
ZVS operation is discussed. Analysis and characterization of
the different modes of operation of the converter is done.
The new step down converter topology has high efficiency
compared to classical buck converters and other ZVS based
step down converters. It eliminates the drawbacks of
existing ZVS topologies such as large number of
components, circulating currents, high losses etc. Also it has
a compact construction and has very good voltage regulation
with simple control requirements.
REFERENCES
[1] S.Pattnaik, A. K. Panda, and K. Mahapatra,
"Efficiency improvement of synchronous buck
converter by passive auxiliary circuit," IEEE Trans.
Ind. Appl., vol. 46, no. 6, pp.2511-2517, Nov./Dec.
2010.
[2] H. Mao, O. A. Rahman, and I. Batarseh, "Zerovoltage-switching
DCDC
converters
with
synchronous rectifiers," IEEE Trans. Power Electron,
vol. 23, no. 1, pp. 269-378, Jan.2008.
[3] S. Urgun, "Zero-voltage transition-zero-current
transition pulse width modulation DC-DC buck
converter with zero-voltage switching-zero- current
switching auxiliary circuit," IET Power Electron., vol.
5, no. 5, pp. 627-634, May 2012.
[4] B. P. Divakar, K. W. E. Cheng, and D. Sutanto,
"Zero-voltage and zero- current switching buck-boost
converter with low voltage and current stresses," IET
Power Electron., vol. 1,no. 3, pp. 297-304, Sep. 2008.
[5] H.L. Do, "Zero-voltage-switching synchronous buck
converter with a coupled inductor," IEEE Trans. Ind.
Electron., vol. 58, no. 8, pp. 3440- 3447, Aug. 2011
[6] T. F. Wu, J. C. Hung, Y. S. Lai, H. S. Nien, and H.
M. Su, "Analysis and design of an active-clamp buck
converter with coupled inductors," in Proc. 20th
Annu. IEEE APEC, 2005, vol. 1, pp. 399-405
[7] M. R. Mohammadi and H. Farzanehfard, "New
family of zero-voltage- transition PWM bidirectional
converters with coupled inductors," IEEE Trans. Ind.
Electron., vol. 59, no.2, pp. 912-919, Feb. 2012
[8] Sung-Sae Lee "Step-Down Converter with efficient
ZVS Operation with load variation" IEEE Trans.
Ind. Electron, vol. 61, no. 1, january 2014
ISSN 2348-7852 (Print) | ISSN 2348-7860 (Online)
(This work is licensed under a Creative Commons Attribution 4.0 International License.)
http://www.ijre.org