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A Self-Driven Active Clamp Forward Converter

IEEE TRANSACTIONS ON CIRCUITS AND SYSTEMS—II:EXPRESS BRIEFS,VOL.51,NO.10,OCTOBER 2004549

A Self-Driven Active Clamp Forward Converter

Using the Auxiliary Winding of the

Power Transformer

Bum-Sun Lim,Hee-Jun Kim,and Won-Sup Chung

Abstract—This study proposes a new self-driven active clamp forward converter eliminating the extra drive circuit for the ac-tive clamp switch.The converter used the auxiliary winding of the power transformer to drive the active clamp switch and a simple RC circuit to get the dead time between the two switches.The oper-ation principle was presented and experimental results were used to verify theoretical predictions.A 100-W (5V/20A)prototype con-verter that only exhibited 1.5-turn winding number in the auxiliary winding was sufficient to drive the active clamp switch on the input of 50V .Finally,the measured efficiency of the converter was pre-sented and the maximum efficiency of 91%was obtained.Index Terms—Active clamp forward converter,active clamp switch,auxiliary winding,dead time.

N OMENCLATURE

Input

voltage 50V .Output

A Self-Driven Active Clamp Forward Converter

voltage 5V .Output

power

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

100W.Switching

frequency

217kHz

(

4.6

s).

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

8.

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

68

nF.

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

.150

pF.

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

2

H.

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

1600

F.

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

IRF23N15D.

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

IRF6216.

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

and

IRF38035

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

Transformer core PLT 22/16/2.5(Feroxcube).Choke core

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

FE I-18/710HL (NICERA).I.I NTRODUCTION

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

The active clamp forward converter is one of the most suit-able topologies to achieve high efficiency at higher frequencies for low-and medium-power applications [1].In the converter,

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

Manuscript received March 2,2003;revised March 31,2004.This work was supported by Korea Research Foundation under Grant KRF-2003-041-D00244.This paper was recommended by Associate Editor I.A.Hiskens.

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

B.-S.Lim is with the Dong Ah Elecomm Company,Yongin 449-820,Korea.H.-J.Kim is with the School of Electrical Engineering and Computer Science,Hanyang University,Ansan 425-791,Korea (e-mail:hjkim@hanyang.ac.kr).W.-S.Chung is with the Department of Semiconductor Engineering,Chongju University,Chongju 360-764,Korea.

Digital Object Identifier 10.1109/TCSII.2004.836039

the active clamp circuit,composed of the clamp switch and the clamp capacitor,is used to suppress voltage stress at the main switch and to recycle the energy trapped in the leakage and mag-netizing inductance of the power transformer [2],[3].The active clamp circuit also provides the flux reset of the power trans-former,thus offering the extension of the maximum duty cycle at the power switches beyond 50%without any extra reset cir-cuits [4].However,in the conventional active clamp forward converter,since the active clamp switch is floated,an extra cir-cuit is required to drive this switch.Furthermore,to obtain the dead time between the two driving signals for the main and ac-tive clamp switches,more extra time-delay circuits are required for each drive circuit.

This paper presents a new self-driven active clamp forward converter that eliminates the extra drive circuit for the active clamp switch.In this proposed converter,the auxiliary winding of the power transformer is used to drive the active clamp switch.A very simple RC circuit is added to get the dead time between the two switches.The operation principle of the converter cir-cuit is described in Section II.Experimental results on a 100-W prototype converter (50-V input and 5-V output)are discussed in Section III.

II.C IRCUIT D ESCRIPTION AND O PERATION

Fig.1shows the circuit diagram of the proposed active clamp forward converter.The active clamp

switch that is p-type

MOSFET and the

capacitor

form the active clamp circuit.The coupled auxiliary

winding

of the power

transformer is used to

drive .The dead time when two

switches

and

are both off is required to avoid an arm short of the two switches,so a simple RC circuit is added to obtain the dead

time.Two

switches

and at the secondary side

of form a synchronous rectification circuit to improve the converter’s ef-ficiency.Fig.2shows the key waveforms of the proposed con-verter circuit.

The auxiliary winding

voltage

is directly proportional to the primary winding voltage and generates the driving

signal

for with a simple RC delay circuit.Between the two driving

signals,

for

and ,there are two dead time

durations,

and .The negative-going edge

of is ex-pressed

by

(1)

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter

1057-7130/04$20.00©2004IEEE

A Self-Driven Active Clamp Forward Converter

A Self-Driven Active Clamp Forward Converter