LM5050-1: surge issue

Tommy Tzeng

Part Number: LM5050-1

Hi Sir,

when performing a surge, common mode test, i found that the LM5050 Gate will drop and cause the output voltage to power down.

as confirmed that as long as the IC GND is connected to the primary side GND or the ground through a Y or X capacitor, this phenomenon will happen, have any idea or suggestion solution.

CH1: 55V output voltage

CH2: LM5050 pin5-pin4 voltage

over 5 years ago

0 Rakesh over 5 years ago

TI__Guru** 105361 points

Hi Tommy,

Can you share schematic and the applied surge profile details to analyze.

Regards, Rakesh

0 Tommy Tzeng over 5 years ago in reply to Rakesh

Genius 5690 points

Hi Rakesh,

surge a hoght voltage(4.4kv) between one end of AC and the ground.

UOR2 is LM5050, is it possible to add circuit or adjust the IC in any way to prevent this happening.

0 Karikalan Selvaraj over 5 years ago in reply to Tommy Tzeng

TI__Genius 16305 points

Hi Tommy,

Surge test is a positive 4kv pulse or negative 4kv pulse.

For negative surge test, we need to have diode between IC GND and system GND and we dont see that diode in the schematic.

Can you please share a better picture of the schematic with primary side included to debug this faster.

Also additional capture of the input current or the MOSFET current of Q43 will help further.

Regards,
Kari.

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LM5050-1: surge issue