SC Protection using SEA05

[YAJUSH]

Dear ST Technical Support Team,

I am currently working on the protection implementation of a flyback SMPS. I found the SEA05 suitable for CC/CV regulation due to its low component count, small footprint, and simple implementation.

I would like to clarify the behavior of the SEA05 during a short-circuit condition.

Our converter specifications are:

• Input voltage: 110 VDC nominal
• Output voltage: 15 V
• Output current: 5 A

During a hard short circuit, the output voltage may fall close to 0 V. If the SEA05 is powered from Vout, its VCC will also fall below the specified minimum operating voltage of 3.5 V.

In this condition, can the SEA05 still sink the optocoupler LED current through its output and maintain CC control, or does the IC stop operating once VCC falls below 3.5 V?

If the SEA05 cannot provide CC control under this condition, please suggest a recommended method for implementing short-circuit protection with the SEA05.

Thank you for your support.

Best regards,

Yajush

[Peter BENSCH]

Welcome ​@YAJUSH, to the community!

Correct, if the SEA05 is powered from Vout, then during a hard short circuit VCC will likely fall below its 3.5V minimum operating voltage, so the IC can no longer guarantee proper CC control.

For reliable short-circuit handling, you should consider:

• powering the SEA05 from a separate auxiliary supply, for example a second secondary winding, or
• adding a hold-up supply for VCC, if the short duration is very limited
• and implementing a primary-side overcurrent protection mode such as hiccup/fault shutdown

Using a separate supply for short-circuit detection/control is the most robust approach.

Regards
/Peter