I was looking around for a voltage regulator when I thought of this, so it might be completely crazy. And I'm sorry if it is.


Could I use a PWM speed controller as a voltage regulator if I were to use a cap to "smooth" out the voltage, and a simple four diode full wave rectifier to make sure the voltage never goes negative?

And I apologize if this is a ridiculous question. I don't know much about PWM or voltage regulators.


2 Answers 2


No you can't. You need an inductor, which 'reduces' your idea to the well-known concept of a switched regulator.

The problem with your idea is that there is some resistance in the path between your power source and the capacitor, and this resistance will dissipate the heat that would otheriwse be dissipated by the linear element (pass transistor or the like). Switching does not help. An indiductor does help, because it stores the energy (and lateron releases it) instead of dissipating it.

Just in case you wonder (as I did long long ago): reducing the resistance does not help. You can prove mathematically that as the resistance approaches 0 the problem stays the same. An no, you can not get it to be zero, which is just as well, because then the current would become infinte, which (at the very least) would give 'interesting' magnetic effects.

Using PWM to deliver a 'reduced' power or as an Digital-to-Analog converter works only when you either

  • smooth the PWM output with a filter (you can use a simple firts-order RC if dissipation and bandwith are no issues), or

  • the thing you deliver the PWM to does not need a smooth supply (motors, lamps, heaters, etc all fall in this category).

  • \$\begingroup\$ I suppose I could make a PCB with YBCO and submerge it in LN2. But that brings up some other problems.... Such as mobility and I really don't see that being a long term solution. :) \$\endgroup\$
    – Sponge Bob
    Commented Jun 29, 2012 at 18:40
  • 1
    \$\begingroup\$ The simplest way to understand why the inductor and circulating diode are necessary in a switcher is to figure out where all the electrons are going. Without the circulating diode, every electron going through the load would have to go through the supply, so the number of electrons per second going through the load would have to equal the number per second coming from the supply, meaning load current and supply current would have to be equal. Without the inductor, nothing would draw any electrons through the circulating diode. \$\endgroup\$
    – supercat
    Commented Jun 29, 2012 at 21:16

A PWM may be used to produce a reference voltage, but cannot very well be used to directly regulate a supply voltage, since the voltage resulting from any particular PWM level will vary with load. One may attempt to use a PWM to switch a supply on and off, and use output feedback to adjust the PWM as necessary to deal with changing load conditions, but in practice it's generally better to use circuitry which was designed for voltage regulation.


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