Hello, hope everyone has a great day !
I'm working on this shunt regulator project, a high voltage (250-300V) design for tube amps. The error amplifier is a vanilla LM324 with a separate supply (labelled Vcc below) external to the regulator board. See schematic below.
I have made the error amplifier section as a separate board and it seems to work as expected. However for a build where it would be integrated in the whole regulator I have outstanding questions:
Regards.
I'm working on this shunt regulator project, a high voltage (250-300V) design for tube amps. The error amplifier is a vanilla LM324 with a separate supply (labelled Vcc below) external to the regulator board. See schematic below.
I have made the error amplifier section as a separate board and it seems to work as expected. However for a build where it would be integrated in the whole regulator I have outstanding questions:
- I placed the final load resistor R_load2 on the separate board so measurements could be made, but is it necessary now that the output drives the mosfet gate?
- In a general sense, are load resistors needed between cascaded op amp stages and if yes what are the requirements for determing an optimal value? Or on the contrary are they detrimental to the performance? For example in my circuit is the first gain stage load resistor R_load1 necessary? I have put large-ish values for R_load1 ansd R_load12 so as to not load the stages too much.
- Should I put a series resistor on the non-inverting input of the first gain stage for protection? The error voltage potential divider's top resistor will limit current for positive swings but what about the current from the speed-up capacitor C1 or in the case of reverse ground voltage when schottky resistor D9 starts to conduct? If a series resistor is needed I think it should to be equal to the inverting input resistor Rg1 (10K) yes?
- The LM324 is a bipolar input opamp, so it needs some input current. Given the high impedance of the error voltage potential divider, should a FET-input opamp be used instead? I have read somewhere that FET inputs are sensitive to noise voltage, not sure if it would be better suited for this task. My understanding is that the current draw of the bipolar LM324 input would just add to the divider chain current and the offset in output voltage can be compensated by adjusting the reference voltage.
Regards.
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