How can I switch 100 Amps at VERY low voltage?

Try a google search using keywords:

multiphase buck converter (no quotes)

or else try searching the sites at

or The goggle search even turned up a wikipedia entry for general information on the concept.

This looks like a perfect match for my needs and a very affordable price - thank you! The only difficulty I can see is the package itself is not something I am used to where it comes to making connections and heat sinking. I don't suppose I could impose on you to ask if there is a similarly handy device in a more easily mounted package (something more "hobbyist class")?

I didn't look at (scrutinize) the spec sheet yet, but I do wonder how many amps these will support without any heat sink ... perhaps with 2 to 4 in each leg I could get by with a cooling fan?

Yes, the next hurdle after choosing a device ... the driving circuit(s). As much work as getting to that point has been, I think I'm looking forward to that .

THANK YOU RL!!!!!!! I SUSPECT MY SEARCH FOR THE RIGHT DEVICE IS COMING TO A CLOSE.

Now to concentrate on the other aspects ... making a circuit board, finding the high amp capable hardware, and, perhaps, canceling on the two SCR's (? --- simpler solution, but I bet the on resistance is much higher than can be achieved this way).

Thanks again, Steve K.

Try the IRF2204PB from digikey for ~$3.50 each.

16 will cost you about $50.

this is an H bridge circuit. Since your supply voltage is so small you don't need T5, T6 R1, or R2 to drive the high side gates. You can drive them directly.

A good quad mosfet driver for this would be the TC4467COE also from digikey.

To operate you turn on T4 then T1 for positive voltage across the motor. Then turn them both off. Then turn on T3 then T4.

If you turn on the top and bottom fet at the same time you effectively short your supply t ground through the mosfets. Usually the would blow the FETs or the supply but in your case it might not be so critical.

Each of the 4 mosfets in the H bridge should actually be a parelleled est of

4 mosfets to reduct teh RDS to below 1mohm.

when dealing with 100 amps, you had better have very heavy wires and PC board traces.

You also need a decent heat sink to mount them too. 10-20 watts will be dissipated in the H-bridge mosfets.

good luck

R Legg has suggested the most practical method, ie. the use of the H-Bridge using parallelled MOSFETS.

What you seem to be trying to achieve is akin to the H-bridge inverter used in sinewave (or modified sine) DC - AC inverters for 50/60Hz power generation, except that you are switching at a much lower frequency.

University of Texas Prof H. Mack Grady has some interesting course material on-line here

Look under Course Materials/Materials for EE362L... for stuff on H-bridge inverter, MOSFET firing etc.

I'd be inclined to look at a rotary switch for the sort of rates you are talking about. But it will be a very special rotary switch!

Yikes!

I'd be trying to think in a 'plumbing' mode - where will the heat be and how can I get rid of it?

DC drive of around 150 HP will work just fine. one for each direction operating in Armature feed back..

Or just get a DC amplifier.

--
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

Switching control comes from the bridge...

I've got a good start with all the info this thread has provided - thanks to all!

You never mentioned just what you plan to use for your original power supply to get the 100 ADC. If you can allow some dead time in between transitions, turning the power supply on and off might be the easiest way to go. This is essentially what I was talking about with the buck converter multiphase approach. The converter would actually be converting the power from a higher voltage/lower amperage source.

I would recommend having the driver IC very close (within 1 - 2 inches) of hte modfet gates. I would also recommend putting a small 10 ohm resistor directly to the gate and a 16V zener between the gate and source of each mosfet. This will kill and oscillation between the wiring undctance ang the gte capacitance and clamp and spikes that might make it get on the gate.

You don't want long wires between the driver and the mosfets.

I would strongly recommend twisting the source and return wires for the 100A to reduce the amount of magnetic field generated.

Yeah, he did. See his post in this thread for Sunday, February 04, 2007 1:04 PM.