AN4007 datasheet(23/33 Pages) STMICROELECTRONICS

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AN4007

Protection features

Doc ID 022455 Rev 2

23/33

Figure 24.

Overvoltage event: OVP triggering (magnification)

2.3

Secondary winding short-circuit and transformer saturation

protection

The VIPER37LE is equipped with a hiccup mode overcurrent protection level.

If the drain current exceeds the second overcurrent threshold, the device enters a warning

state, at the next switching cycle, if the hiccup mode level is exceeded again, the device

assumes that a secondary winding short-circuit or a hard saturation of the transformer has

occurred, so the device stops operating and the MOSFET is no longer allowed to switch on.

In order to enable the MOSFET to switch on again, the VCC voltage must be recycled down

to VCCrestart and then up to VCCon. If the cause of the hiccup mode overcurrent protection

activation is not removed, the device again enters auto-restart mode. The extremely low

repetition rate ensures safe and reliable operation.

This protection was tested on the demonstration board. The secondary winding of the

transformer was shorted in different operating conditions.

Figure 25 and 26 show the

behavior of the system during fault.

AM11363v1

Ch2 (Max): 3.08 V

M: 20.0 µs/div

VOUT

I DRAIN

VCONT

AN4007 Datenblatt(PDF) 23 Page - STMicroelectronics