User`s guide

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SMPS AC/DC Reference Design User’s Guide

3.3.2 Phase-Shift ZVT Control Scheme

3.3.2.1 ZVT RESOURCE ALLOCATION

The control scheme for the Phase-Shift ZVT Converter is shown in Figure 3-5. A

schematic of the Phase-Shift ZVT Converter is shown in Figure 3-6.

FIGURE 3-5: PHASE-SHIFT ZVT CONVERTER CONTROL SCHEME

The ZVT converter uses voltage mode control to maintain a constant output voltage.

The circuit configuration of the ZVT converter has the output voltage (the parameter to

be controlled) on the secondary side of the isolation barrier (refer to Figure 3-8).

The SMPS AC/DC Reference Design implements the ZVT voltage feedback by

measuring the output voltage using the secondary side dsPIC DSC. The Most

Significant 8 bits of data are transmitted back to the primary side dsPIC DSC through

a UART communication channel.

The data received by the primary side dsPIC DSC is right-shifted by two bits (for 10-bit

data) and is compared with the voltage reference to produce the voltage error. The

voltage error compensator is then executed in the ADC ISR.

The output of the voltage error compensator is feed into the phase-shifted PWM. The

Phase-Shift ZVT converter uses the unique phase-shifting capability of the PWM

module in the dsPIC33FJ16GS504. The phase of the PWM signal can be modified by

simply writing the new value in the appropriate Special Function Register in the PWM

module.

Voltage

Reference

VOUT

ZVT

Transformer

Voltage

Update

Phase

Overcurrent

Protection

ZVT Current Sense

OUT

Sense

Voltage Error

Compensator

ADC

1001011011

1011001010

S&H

Rectifier

Optocoupler

S&H

for overcurrent

protection

ADC

1011001010

UART

Feedback

PWM