i've found a h bridge circuit. i need to supply 12V to the motor, and my signal can only be 5V. when the signal supply to a, the motor goes forward, when the signal supply to b, it goes reverse. i've tried both the circuits A and B. it gives only 5.xxV output. but when i change the signal to 12V, it gives a 11.xx v output. can anyone help me??
i need to control it with only 5V signal to move the motor in both direction in 12V.
thanks for helping.

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Well you need to supply 12V to A and B otherwise the top switches wont switch (I am supprised they are!!!! esp since the emitter will be jumping)


If you want to control from 5V you will need another BJT that takes in 5V to turn-on, but the Collector (via a resistor) is tied to 12V, the collector connection (which will now toggle between 12V and ~0.6V) can now be tied to the point you want to control

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?? i don't really get what u mean..?? how to use another bjt to turn it on?? can u show me the circuit construction??

 

can anyone solve my problem??? thanks!!

 

That's a very poor design, have a look at http://www.lpilsley.co.uk/cybot/driver.htm for some better ideas.

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anyone can solve my h-bridge problem??

 

Did you miss Nigel's last post?

 

i couldn't find the transistor at my place from Nigel's circuit. and.. he said that the circuit design is poor.. but do u know that, i pick it from the bonzana's book? try to respect others.

 

I don't know Mr. Bonzana but now that you know his circuit does not work off a 5V signal, maybe you should try googling for alternate H-bridge designs that do.

Here are a few I have found (taking from the first page of a google search).

http://www.mcmanis.com/chuck/Robotic...t-circuit.html
http://www.bobblick.com/techref/proj...e/hbridge.html
http://www3.telus.net/chemelec/Proje...H-Bridge-1.png

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"Having to do with Motion Control"

 

Just because it was in a book doesn't mean it's any good!, and it's still a VERY poor circuit, and doesn't deserve any respect!.

The example I gave the link to is from a magazine robot called Cybot, it's not intended to be copied 'as is' but as an example of how an H-bridge works. I wouldn't say it's a great example, but it is considerably better than the NPN only example!.

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okay... but i can't get the transistor in my place.. do u have other circuits?? thanks..

 

You don't need the specific transistors, use what's available, bearing in mind the current requirements of your motors.

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Using polarised capacitor across the motor terminals does not deserve any respect either. :twisted:

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L.Chung

 

You will notice I pointed that out in my explanation of the circuit! :roll:

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if other transistor can be used.. then what is the transistor?? please help.. thanks!!