voltage boost

By now I am quite familiar with dropping voltage, through a regulator or otherwise, to needed levels for lower-voltage portions of a circuit.

What about going the other way? If i have a 3.3v source, and i want to briefly hit a switch or motor with 5v, is there any way to do that? I imagine a capacitor or some kind of transformer may help. or is the only possibility to source higher power in with a transistor?

thanks

Voltage boost regulators are readily available. There are many ways to generate higher voltage from low voltage, but switching action is required.

A simple transistor would do that providing you have the voltage to step up to.

Couple of options:

If you have 5v, just aren't running the microcontroller on it, switch the load with a transistor and be done with it.

If you don't have 5v... Use a boost converter (these can be had for under $2 on ebay, adjustable) if you need much current.

You can also - if the current required is very low, and you're space constrained - use a switched capacitor voltage doubler, or use the voltage doubler on a MAX232... But this only gives you the doubled (and doubled inverted, in the case of max232) voltage, not an adjustable one like the boost converters, and it's not as efficient.

Right, if I had 5v onboard a transistor would be great - but this is a 3.3v uC and that is all i have on the device at the moment. i will look for a boost regulator or switched capacitor, thanks!

Pololu offers a nice selection of boost regulators at http://www.pololu.com/category/132/step-up-voltage-regulators

We do have to be careful here in what is being proposed.

If the situation is that you only have a 3.3V supply (generally a lithium battery) and you need 5V for some function, then you can use a boost regulator to boost that supply voltage. These generally have a “control” pin on the chip which will switch it on and off under control of your MCU, or you use a transistor to switch your device from the output of the boost regulator.

What you can not do, is to use the boost regulator to increase the voltage from an output pin of the Arduino. Nor will it be profitable to use a transistor to switch the 3.3V input to the boost regulator.

And of course, if your actual supply voltage is higher and you have a regulator producing your 3.3V as you do on a Pro Mini or such, then you use a 5V regulator fed by that higher supply voltage and a transistor to switch.