DER286 30W Short-circuit feature not run

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we are designing 30W (30V,1A) following DER286 (capacitor design) ,
but when we short 2 output pin, the IC does not shutdown to protect LED load, the output current is still=3A. all components value are same and in DER286. only transformer change to EER28 core instead of PQ26/25 in DER286.

Any expert can advise reason and solution for the short-circuit problem.

It is necessary to measure the bias voltage when the output is shorted.

The feedback current has to go down lower than the auto restart threshold level when the output is shorted.

you are correct!
the issue is bias voltage (c10 voltage) when output is shorted is about 33V-45V depend on input voltage (100-270VAC), and 26-35V at normal status (full load).
that mean at some input voltage Bias voltage at normal running is quite same as short circuit status, the threshold diode VR3 is 39V => IC can not shutdown.

could you help to advise solution?

Input:90-265VAC
Out: 30V, 1A

thanks
Kieu Hung
Vietnam

The leakage inductance of your transformer might be too high, and it might cause high peak charging effect on the bias voltage.

You need to figure out how to reduce the peak charging effect by reducing eh leakage inductance with adding snubber or spliting winding, etc.

Hi
attached is our transformer design using PIsls Designer.
our leakage inductance now is about 38uH (when Sec and Bias are shorted)
could you have a look and advise how to adding scrubber and spiting winding.

thanks for your good support!

Measure the bias voltage with shorted right across secondary winding in circuit, not output, which should be under 5V.

If not, the leakage inductance and parasitic resisitance between secondary winding to bias output might be too high.

If it does, the leakage inductance and parasitic resisitance of output might be too high.

Measure the bias voltage with shorted right across secondary winding in circuit, not output, which should be under 5V.

If not, the leakage inductance and parasitic resisitance between secondary winding to bias output might be too high.

If it does, the leakage inductance and parasitic resisitance of output might be too high.