AN3203 datasheet(17/49 Pages) STMICROELECTRONICS

17 / 49 page

AN3203

Complete system

Doc ID 17402 Rev 2

17/49

Complete system

3.1

Overvoltage protection

Every output is protected against overvoltage. The +12 V, +5 V and +3.3 V are monitored on

the auxiliary power supply schematic page. They use three Zener diodes to fix the three

overvoltage thresholds. In case one of the three voltages exceeds its threshold the latch

realized with Q604 and Q605 is turned on and the VCC for the L6591 and L6563S is

removed.

The two outputs +5 V and +3.3 V also have an overvoltage protection integrated into the

L6727 controller.

The +5 V_SB output is protected using the OVP protection of the VIPer27H that senses its

output voltage through the auxiliary winding. A threshold on the CONT pin detects the OVP

condition and stops the IC operation. This protection has an auto-restart behavior.

3.2

Load transients

The following figures show the behavior of the outputs during load transients. Each image

shows the transition from 20 % to 100 % of rated current and vice versa for a single output

voltage. The current slope is 0.5 A/µs for all the current variations.

Figure 11.

Load transient on +12 V output

AN3203 Datasheet(PDF) 17 Page - STMicroelectronics