APR343

Document number: DS36884 Rev. 4 - 2

8 of 12

www.diodes.com

December 2014

© Diodes Incorporated

APR343

A Product Line of

Diodes Incorporated

The operation of the SR is described with timing diagram shown in Figure 2. APR343 monitors the MOSFET drain-source voltage. When the drain

turn on and the current will transfer from the body diode into the MOSFET’s channel.

In the process of drain current decreasing linearly toward zero, the drain-source voltage rises synchronically. When it rises over the turn off

Minimum On Time

MOSFET will keep on until the end of the minimum on time.

The Value and Meaning of AREF Resistor

As to DCM operation Flyback converter, after secondary rectifier stops conduction the primary MOSFET Drain-to-source ringing waveform is

resulted from the resonant of primary inductance and equivalent switch device output capacitance. This ringing waveform probably leads to

Synchronous Rectifier error conduction. To avoid this fault happening, APR343 has a special function design by means of volt-second product

second product.

Kqs

*

R

2

Area

AREF



In general, Area1 and Area3 value depend on system design and always are fixed after system design frozen. As to BCD PSR design, the Area1

value changes with primary peak current value and Area3 value generally keeps constant at all of conditions. So the AREF resistor design should

consider the worst case, the minimum primary peak current condition. Since of system design parameter distribution, Area1 and Area3 have

moderate tolerance. So Area2 should be designed between the middle of Area1 and Area3 to keep enough design margin.

Area1

Kqs

*

R

3

Area

AREF





Area3

Figure 3. AREF Function

SR Minimum Operating Voltage

SR driver will be disabled.