I'm currently trying to build a lab bench power supply for myself. It should reach 40V at 5A. I will also try to control it digitally with a µC.
I suggest starting at a lower voltage and current to get a better idea of what works and what does not work.
So far I only designed the analog-power output stage of the supply I wanted to later add a Buck pre-regulator before the linear regulator. I just want to know if this design is viable or should I just scrap the idea and begin new.
The design is not viable. Scrap the idea and begin new.
1. T1 adds uncontrolled voltage gain within the current control loop which will make frequency compensation near to impossible. Replace T1 with a diode and PNP emitter follower or use a different way to combine the voltage and current loops.
2. Cascading current sense amplifier U2 with current error amplifier U1B makes frequency compensation more difficult and is not necessary in any case. Both functions can be performed in the same stage. (1)
3. Output capacitor C3 is unusually small for a general purpose 5 amp supply but not for a higher performance one with faster current limiting. But a low output capacitance per amp requires careful attention to frequency compensation. Placing the current shunt in series with the output as shown actually makes this easier if AC feedback is taken from before the current shunt because it adds a zero (phase lead) to the frequency compensation just like the ESR of the output capacitor does.
4. C1 is useless and will just cause tears.
5. The LT1013 (and most operational amplifiers) will have difficulty driving the input capacitance of a power MOSFET output stage. Consider adding a power buffer to improve performance.
6. C2 and C4 are attempts to meet outrageous frequency compensation requirements and should not be required.
(1) Instead of using current sense amplifier U2 to create a ground referenced voltage representing the output current, do it in reverse and create an output referenced voltage representing the maximum current. In other words, level shift the current control signal to the output voltage level. Then the error amplifier for the current control loop just follows the output voltage and there is only one stage. (2)
(2) Of course this does not allow easy read-back of the output current level in a digitally controlled design. I might use a separate current shunt amplifier as shown to make a ground referenced signal just for that although this makes calibration more complex.