AN2753 datasheet(21/31 Pages) STMICROELECTRONICS

21 / 31 page

AN2753

Precision of the regulation and output voltage ripple

Doc ID 14654 Rev 2

21/31

Figure 23.

2nd OCP protection tripping

In Figure 23 when the board is working in full load condition with an input voltage of 115 VAC

the secondary winding has been shorted. The short condition on the secondary winding

leads to high drain current. After two switching cycles, the system stops and continuous

running with high currents in the primary as well as in the secondary windings are avoided

Figure 24.

Operating with secondary winding shorted

3.6

Output overvoltage protection

Monitoring the voltage across the auxiliary winding during the MOSFET off time, through the

D2 diode and the resistor divider R3 and R14 (see Figure 2) connected to the CONT pin of

the VIPer17, allows the implementation of the output overvoltage protection. If the voltage

on CONT pin exceeds the VOVP thresholds (3 V typ.) an overvoltage event is assumed and

CH2: VFB (Light blue)

CH3: VDRAIN (Purple)

CH4: IDRAIN (Green)

Test condition:

VIN= 11 VAC

Full load before short

CH1: VDD (Yellow)

CH2: VFB (Light blue)

CH4: IDRAIN (Green)

Test condition

VIN=115

Secondary winding

shorted

AN2753 Datasheet(PDF) 21 Page - STMicroelectronics