Thread: High power h-bridge

I need to make an H-Bridge that will be used basically as a heavy duty servo which is hooked to my microcontroller. It needs to be able to drive a motor that is about 20A @ 12V (wiper motor). I have searched for days on how to build one but I can't find one that is over 2A. I will probably have to make my own so I need some help.

I found this page to be very helpful
http://www.dprg.org/tutorials/1998-04a/
but I can't find any PNP MOSFETS that are equal to a NPN MOSFET that I find.

Does anybody know of a PNP, NPN combo that will work for me?

Thanks

I searched for that chip on findchips.com but it wasn't found. Also on Yahoo, there was no matches.

i don't know if it will serve your purpose but you could check out the hbridge at the site Robot room, you'll get resources for other circuits as well

No, I would not use relays. I would do as suggested and use some very high current (read low RDSon) discrete mosfets. Building an h-bridge is very straightforward. I would pick the lowest voltage you are comfortable with and then find one with sufficient current handling.

"npn" and "pnp" is a term for bipolar. MOSFETs are called n-channel and p-channel, or PMOS/NMOS.

You would want to hook your two PWM channels to the n-channels pulling the outputs to ground. The p-channel is at 12V so the gate can't be switched directly, you will use a small MOSFET or npn to pull down the gate and a pullup pulls it back up.

PMOS is inherently lower gain and higher rds than NMOS. Not that you can't find PMOS with a lower rds than an NMOS, but in the end the biggest one PMOS you're going to find is worse than the NMOS, at least for a particular price. Go to http://www.digikey.com Seach for MOSFET, select p-channel, click "Apply Filters", then select the current you want AND, using the shift key, select every current higher than what you want.

You can also build a purely NMOS h-bridge. That reduces the number of different components and for equivalent RDSon values, N channel parts are lower cost and more readily available. All of mine are NMOS only. The trick is to use a small voltage doubler circuit to raise the gate voltage to 2Vcc so that the n-channel parts at the top of the bridge turn on. You have to be running high enough voltage so that the gate is 4 to 7 or more volts beyond the voltage at the drain node. For instance, with a 12V motor, you would generate 24V which is enough for the mosfets to work. You can use any of the ICL7660 doubler circuits. Alternatively, there are special parts such as the HIP4081 (i might be wrong about the part number) that is specifically designed to interface directly to an all n-channel h-bridge.

I have standardized on the IR331* for the high side of h-bridges. These parts have an adjustable current limit, up to 90 Amps. The current limit is set with a single resistor. The output current is proportional to the current limit voltage so the current can be measured with a simple ADC. They are on when the input is off so they can be driven with a small mosfet directly from a microprocessor. The current limit makes the whole h-bridge very robust. I have used it with wiper motors and larger motors. By monitoring the bridge current I can operate motors until they stall, avoiding the need for limit switches and circuitry. The overcurrent response is fast.

These work well with motors but the overcurrent response is so fast that they won't drive headlights, which have over 10:1 in rush (2 60w bulbs have over 100A in rush cold).

If you want more info you can e-mail me at stephen@copper.net - I probably won't check this site very often. If you want a couple of surface mount IR 3312 (30A) or IR3310 (100A) I could sent them to you. This offer is only good for a few people.

- Stephenvb

Yes, you can make a vltage doubler and use all n-mos. I use the IR331* and suggest it because you don't need a voltage doubler and because it provides short circuit protection. At such high currents shoot-through, a wiring error or a short destroys the mosfets, connectors and circuit boards. In an h-bridge high side protection also protects the low side mosfets. I make mistakes and I have had wires come loose and motors fail so this is important to me. If you never have these things happen it would be of no use at all.