Need to make variable DC power supply 0 -100 v current 2 amps. With coarce snd fine addjustments for voltage with 3 1/2 digit meters for both volt and current

Hi Swatagam, could you please explain to me in detail the formula, resistance in parallel. I understand how to calculate for two resistors in parallel but don’t know how to calculate for more then two, beyond many textbooks just stating the formula as 1\R1+ R2+R3+R4…. Please detail this concept of reciprocals. P.s. I’m a hobbyist. Thank you very much for caring and sharing such a wonderful site. P.s. I’m a hobbyist.

Ksmani says

Need to make variable DC power supply 0 -100 v current 2 amps. With coarce snd fine addjustments for voltage with 3 1/2 digit meters for both volt and current

Swagatam says

If you use a linear approach, there will be a lot of heat dissipation. Better to use a transformer based design.

A linear design is shown below:

https://www.homemade-circuits.com/universal-variable-power-supply-circuit/

you can upgrade it to 100V by replacing the power transistors accordingly, and by changing R3 to 10K 1 watt

moboy says

Hi Swatagam, could you please explain to me in detail the formula, resistance in parallel. I understand how to calculate for two resistors in parallel but don’t know how to calculate for more then two, beyond many textbooks just stating the formula as 1\R1+ R2+R3+R4…. Please detail this concept of reciprocals. P.s. I’m a hobbyist.

Thank you very much for caring and sharing such a wonderful site. P.s. I’m a hobbyist.

Swagatam says

Thank you moboy, It is actually very basic, here’s the formula for calculating resistors in parallel:

1/R = 1/R1 + 1/R2 + 1/R3….1/Rn