Author Topic: Feedback in "isolated" DC-DC  (Read 174 times)

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Offline nihialTopic starter

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Feedback in "isolated" DC-DC
« on: January 24, 2025, 03:55:33 pm »
Hi,

I have a 28-180DCDC power supply whose controller got obsolete and I want to replace it.

I found an alternative (NCP1397A) but the feedback isn't working the same way as the previous chip.
The previous chip had the following logic : the lower the voltage the higher the switching frequency and pulse skip at some point.
The new one has the opposite logic.

Even if the DCDC uses a isolated topolgy, the output isn't isolated so the feedback doesn't need to be isolated.
The feedback that was used in the previous design is an integrator you can see below, the reason of the initial designer was to avoid at all cost a optocoupler because of space constraints.




Now since the logic has been inverted I can't use that feedback circuit anymore. I'm looking for an elegant way with the minimum real estate used but I can't find anything that I find decent.
I have also absolutely no idea how the feedback in the isolated case are designed in the case I have no choice but to squeeze an optocoupler.
Any idea/help would be appreciated

Best regards
 


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