User`s guide

Introduction

Power is transferred to the secondary only when the diagonal switches are ON. If the

top or bottom switches of both legs are ON simultaneously, zero voltage is applied

across the transformer primary. Therefore, no power is transferred to the secondary

during this period. When the appropriate diagonal switch is turned OFF, primary current

flows through the output capacitor of the respective MOSFETs causing switch drain

voltage to move toward to the opposite input voltage rail. This creates zero voltage

across the MOSFET to be turned ON next, which creates zero voltage switching when

it turns ON. This is possible when enough circulating current is provided by the

inductive storage energy to charge and discharge the output capacitor of the respective

MOSFETs. Figure 1-12 shows the gate pulse required, and the voltage and current

waveform across the switch and transformer.

The operation of the Phase-Shift ZVT can be divided into different time intervals.

Assuming that the transformer was delivering the power to the load, the current flowing

through primary is I

PK, and the diagonal switch Q1,Q3 was ON, at t = t0, the switch Q3

is turned OFF as shown in Figure 1-12.

FIGURE 1-12: REQUIRED GATE PULSES AND VOLTAGE AND CURRENT ACROSS

PRIMARY

1PWM

2PWM

3PWM

4PWM

Vprimary

t0 t1 t2 t3 t4

(A) = Gate pulse for all switches for Phase-Shift ZVT converter

(B) = Voltage across primary

(A)

(B)

(C)