A problem met in the design of switching power supply

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Martilda
Posts: 1
Joined: Mon Mar 06, 2017 3:51 am

A problem met in the design of switching power supply

Post by Martilda » Mon Mar 06, 2017 8:23 am

Hi, I'm using a switching power supply chip LM2575 to drive the load by turning DC voltage 24V to 1.5V. It works well except a problem...

Everytime when the power’s off, the capacitor C2 (maybe?) will still supply power to the load for a short period. Due to this, I cannot turn off the load immediately.
If the problem is not caused by C2, then what’s the cause?

I wonder if there are any solutions to this problem?

Sorry for my poor English, but I really need your suggestions! Thanks in advance!

Image
(R3 is the load)

David
Posts: 216
Joined: Sun Oct 04, 2015 6:18 pm

Re: A problem met in the design of switching power supply

Post by David » Mon Mar 06, 2017 10:54 am

Try reducing the value of C2. Also, if you need the voltage on R3 to drop very quickly, try a double-pole switch - one pole to switch the input to the chip, the other to switch the supply to R3.

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