but then, i found out, it has not great impedance when it goes negative voltage (see 2nd picture below), i'm thinking i will use the Vout into the LM317 ADJ pin and looking at LM317 schematics, ADJ pin needs to withdraw current, the above setup cant sink/drain/suck current satisfactory, so i spent the whole evening to simulate push pull type. below is what i find out to be the best, but i need comment, in case i miss some resistors that will blow up this circuit.
please bear in mind the objective is to control LM317 on high voltage rail (60V) from low voltage opamp rail ±15V. opamp output (10V) will be multiplied by 5 to get 50V Vout and fed to LM317 ADJ pin. high voltage opamp is not available. and please note, the below circuit is using mixed rail setup, where the push pull collector at the bottom is fed to -15V rail, because i want LM317 to output to 0V, so i hope this is safe. dont worry about LM317 input, it will not exceed 37V (Vin - Vout) because we have tracking pre regulator beforehand. if no comment i will assume and hope this wont smoke the low voltage components when i assemble them on the breadboard later, i killed 1 uA741 already because i shorted something on the breadboard, i guess the uA741 got fed with 60V and now its output is broken
any comments? thanks.