Inverting power rail circuit using Buck Converter and Op-Amp in feedback

Thread Starter

rnuss

Joined Mar 12, 2019
2
The attached circuit is used to generate a a -13V power rail from a +13V input. The Buck converter is configured as an inverting buck-boost. Typically it could not provide an output as high in voltage as the input. So I presume the op-amp in the feedback helps to achieve thisschematic.jpg . I would like an explanation of how this works and how R3 and R4 would be selected.
 

Thread Starter

rnuss

Joined Mar 12, 2019
2
The power supply chip is a Richtek RT6200 (0.6A,36V, 1.2MHz Step-Down)

The output is the (top of drawing) -13V

I can't identify the particular op-amp.

Input between +13V and ground
Output between -13V and ground
 

mvas

Joined Jun 19, 2017
538
The attached circuit is used to generate a a -13V power rail from a +13V input. The Buck converter is configured as an inverting buck-boost. Typically it could not provide an output as high in voltage as the input. So I presume the op-amp in the feedback helps to achieve thisView attachment 172143 . I would like an explanation of how this works and how R3 and R4 would be selected.
Feedback Voltage ( FB ) is derived from R1 and R2, which form a voltage divider across the Output of the Inverting Op-Amp
The GAIN of the OP Amp Gain is determined by R3 & R4

I think, you are missing a "Cout" capacitor across the ( -13 V ) output and ground symbol
 
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