AnsweredAssumed Answered

L4970a Output Oscillates

Question asked by carboni.adrian on Mar 4, 2014

I need the following: 24V vehicle input. Allow for 28V. 13.8V @ 10A output. I used an L4970a. My circuit delivers the load, no problem.

On initial switch on with no load, the output is stable. When I place a load up to 10A, it works. When I remove the load, the output oscillates between Vin and 7.5V at 13Hz (75mS) with a sawtooth function. If I place the load on again, it works perfectly.

I searched on the internet and saw a suggestion that I place a load of 0.2A across the output as an offset stabiliser. That didn't work. It also generates another 2.6W of heat. Not so good.

So, the problem occurs after a load is removed. I cannot guarantee that there will always be a load on the output.

I have followed the layout guide-lines from the ST app notes.

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