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Transistor H-bridges Answered

Is it possible to make a transistor H-bridge with PNP transistors or can it only be done with NPN transistors.  As far as my knowledge( or lack thereof) of transistors goes, I think it would be possible, but it would require more than 4 transistors and it would be much more complex, however I could be entirely wrong.  Any input would be helpful, thanks.

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kelseymh

8 years ago

I'm confused.  The H-bridge designs I've seen use both:  one PNP coupled to one NPN on each side of the load. Could you point to an example of a pure NPN H-bridge?

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jpennkelseymh

Answer 8 years ago

Thanks loads to all you guys. I guess I really didn't know what I was talking about, but you have steered me in the right path. Thanks again. :)

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steveastroukkelseymh

Answer 8 years ago

You can do it either way. There are advantages to using NPN transistors over PNP ones, to do with switching speed. Obviously the base drives need sorting out, but so what ?

Steve

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AndyGadget

8 years ago

As Kelsey says, H-bridges usually have 2 PNP and 2 NPN.
Here's a useful guide to them.

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steveastroukAndyGadget

Answer 8 years ago

No, they MAY be complementary, but there aren't USUALLY complementary, especially if the load can float.

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AndyGadgetsteveastrouk

Answer 8 years ago

Hmmm . . . Never seen them used like that.
So, with NPNs, the top pair are running in emitter-follower mode.  Wouldn't the base voltage need to be above the motor supply otherwise you'd be running in linear mode, dropping extra voltage and losing more as heat?

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steveastroukAndyGadget

Answer 8 years ago

Yes, so you use the same drive topologies you use with Mosfets, or optically couple them.