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Hi,
We have two separate LM5023 based flyback bias circuits in our design. At standby, we want to turn off one bias circuit to reduce overall standby power.
To accomplish this, we were planning to pull down the COMP and VSD pins of the LM5023 on the bias we want turned off. We plan on using an opto which will be driven from a secondary micro that will be active during standby. I have attached a simplified schematic. Pulling the COMP pin down to primary GND prevents PWM pulses to the power train and pulling the VSD pin down prevents depletion mode FET turn on to charge the VCC cap.
Just wanted to check if there are any concerns using this method or is there any other more effective method to turn the bias off and reduce standby power further.
Hello Abhiman,
I reviewed the LM5023 data sheet and the comp pin has -132 uA of pull down current. So you should be able to pull down on the comp without damaging the LM5023.
You could also pull down on the soft start pin which is limited at 30 uA to stop the device from switching also.
Pulling the VSD pin low should disable the startup FET and disable it from the circuit so you should be O.K. there.
Regards,
Mike