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L6699D No load condition

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padewinter

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Hi All,

I have a 500W PS build around the L6699D and everything is working good.
Now I found 1 little thing:

If I run the unit in No Load the output is 24Vdc if I take the input voltage (AC) away the output drops a little.
Now if I switch the unit back on (there is still a output voltage of around 23.5Vdc when it is switched on) the output voltage flies up and clamps to the OVP (30Vdc) and it is unable to regulate the voltage down despite that the signals are there.

Now my question is, is this someting I can control or is this a problem in the L6699D and did anyone else run into such a sitiuation?

Hope someone can help me.
Thanks,
Patrick
 

You need a minimum current.

Right from the data sheet:

When the resonant half bridge is lightly loaded or totally unloaded, its switching frequency
reaches its maximum value. To keep the output voltage under control and avoid losing softswitching
in these conditions, there must be some current flowing through the transformer's
magnetizing inductance.
 
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