# Voltage regulation for capacitors

I have four capacitors connected in series and I will apply voltage over them.

The voltage is generated from a DC-motor, and I want to make sure it does not rise above 9V. What is the best way of doing this?

My initial thought was to use a 9V voltage regulator. But as I understand it, if I generate less than 9V (which I will likely do) I will end up losing some voltage even though I don't want to (voltage drop?).

What are some other ways I could limit the voltage?

• I would go with a Zener Diode – MAB Jul 26 '17 at 20:22
• what is maximum current? – Sunnyskyguy EE75 Jul 26 '17 at 20:48

Look at something called a "shunt" regulator. These are regulators that go in parallel to your load to clamp voltage to a maximum level. Zener diodes are a good example (although crude, and gennerally not the best in terms of regulation). For this reason shunt regulators are sometimes represented with a zener diode, even though they may be more complex.

simulate this circuit – Schematic created using CircuitLab

• I interpreted the question as "anything under 9V is acceptable" - the losing some voltage meaning the series voltage drop of the regulator. If this is not what the OP meant. I will come back later to try and update, given he replies to clarify. – Joren Vaes Jul 26 '17 at 20:54
• Thanks for the reply! Yeah, Ideally I want no loss of voltage as a result of implementing a regulator. I'm guessing the Rsource resistor would cause a loss of voltage in this case? What would happen if I don't use the Rsource resistor? I guess it would be like shorting the poles of the DC motor, but would this cause it to break or something? – user2157416 Jul 27 '17 at 8:22
• @user2157416 the rsource will be there in your motor. It is a resistor that represents a combinatin of the resistance of the copper in your source. How big it is depends on the generator, and I just took 1 ohm for the sake of example. – Joren Vaes Jul 27 '17 at 9:24

simulate this circuit – Schematic created using CircuitLab

Drain with < 33V <1mA
with > 36V >1A >9W per Transistor. with insulated heatsink

Use a power zener. To get you over the hurdle.

• you must be assuming this motor generates only xx mA's – Sunnyskyguy EE75 Jul 26 '17 at 21:59