Help needed with H-Bridge components

kochiro

Hello all,
Let me start by saying that I'm still very new to electronics. I'm a software programmer who is slowly learning the hardware side of things.

I'm working on a project that requires an h-bridge. I've seen the one that Chuck McManis did in his tutorial, but I need to bump up the available amperage quite a bit. With a heat sink he states that the h-bridge will handle around 2 amps continuous. I need to have a continuous limit of around 15 amps with a peak load of 20 amps for safety headroom.

I think that this can be accomplished by simply changing out the transistors with higher capacity units or by adding more of them. However I'm not sure what to replace them with or how to add more into the design. I'm also not sure if other components would need to be changed to support the different/extra transistors and extra load.

I'm hoping someone here could answer those questions for me as well as recommending a book or two that would serve as references for a beginner like myself.

Here's the link to his tutorial
www.mcmanis.com/chuck/robotics/tutorial/h-bridge/

And here's the link directly to the page where he shows a completed picture and diagram of it.
www.mcmanis.com/chuck/robotics/tutorial/h-bridge/bjt-use.html

Thanks,
Jay

Beau Schwabe

Something to consider....

With Bipolar Junction Transistors (BJT)'s you are going to loose 1.2 Volts of overhead right
off the bat across the E-C (Emitter Collector) transistor junction. What this means is that
at 15Amps you will need to dissipate 18Watts (P=I*V) of heat that never gets to the motor.

I would strongly recommend a MOSFET H-Bridge version with a low Rds on (<-- Resistance
between the Drain and Source while the transistor is "on")


Here is a link that might help:
www.armory.com/~rstevew/Public/Motors/H-Bridges/Blanchard/h-bridge.htm

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Beau Schwabe

IC Layout Engineer
Parallax, Inc.

Post Edited (Beau Schwabe (Parallax)) : 12/24/2005 3:30:30 PM GMT

LoopyByteloose

He uses a BJT [noparse][[/noparse]Traditional] transistor setup.

With MOSfets, you can easily get the 20amps and the newer MOSfets actually are designed for direct 5 volt switching.

The problem with BJTs is that they require more current to drive more amps and they tend to work in a zone that is neither full on or full off. This zone creates more heat and heat is the source of failures. MOSfets avoid this barrier.

Darlingtons are a paired adaptation of BJTs, but they again begin to have heat problems. But, they do partially solve the demand for more current.

Take a look at 'The Art of Electronics' if you can read at that level. It will clearly explain quite a bit. Otherwise, just keep asking here for help AND SEARCH H-BRIDGES and this topic has been discussed many times.

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"When all think alike, no one is thinking very much.' - Walter Lippmann (1889-1974)

······································································ Warm regards,····· G. Herzog [noparse][[/noparse]·黃鶴 ]·in Taiwan