I have some basic knowledge of SMPS voltage regulation feedback circuit concepts, and basics of control systems theory, mainly conceptually. I've hacked various PSUs and 5V battery chargers to make them variable voltage supplies.
I'd like to learn some more about how power supply engineers determine the values of the capacitors and resistors used in feedback circuits, and would like to mod the following 5V battery charger to output 7.5V as a relatively simple example.
[ The Power Supply ]Type: 5V Battery Charger
[ Primary Side Controller ]STGL LY6805 - Flyback PWM Controller
Topology : QR Flyback
Operation Frequency : Variable
Max Vdd : 28V
Frequency Shuffling : Y
...
Application Example Schematic[ Note 1 ]In the schematic above, on the lower right (secondary side) there is an "IC2"(programmable zener) which could be say a TL431, but in the 5V charger of interest there is the "DK450" instead.
[ Secondary Side Voltage Reference ]DongKe DK450 - 5V Voltage Stabilizing Controller
Circuit DiagramApplication Example Schematics[ Notes 2 ]1. As indicated in the DK450's example schematics above, the 5V charger does not include the resistors(R1,R2, R3) and capacitor(C2) needed in a "normal circuit without DK450", since the DK450 is already optimized for 5V regulation.
2. As I'd like to 'adjust' the output voltage up to 7.5V, I'm thinking that it will be necessary to add in the absent resistors(R1,R2, R3) and capacitor(C2).
[ Questions ]1. How are the values for the resistors(R1,R2, R3) and capacitor(C2) determined?
2. What is a good introductory source(book, web article, YouTube tutorial etc.) that would demystify this topic?
Thanks in advance...