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H-bridge HELP NEEDED ! ! ! ! !

I searched every shop in my area couldnt find a single piece of H.so i thought to make it with logic gates as 7400 series is available. but before i buy i wanna know if my design is feasible? and is there any possibility of damaging of chip (logic gates).i'm using a GEARED MOTOR in my H-bridge

H-Bridge.png23.3 KB

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Your design might be working, but I can’t see how the logical gate would be able to supply the current needed for the motors. I think this is a dead end and would recommend that you take the normal transistor road.

that your circuit will release the magic smoke from your logic gates. I doubt they are meant to supply much more than a few tens of mA (i.e. maybe 25 or 30 mA). The reason, as I understand it, for using transistors is due to their current handling capabilities.

Your logic gate layout seems solid, just the electrical concepts are getting in the way. :) I would imagine connecting the output of the logic gates to a resistor and from there to the base of a suitable transistor would accomplish the pin saving goal of your h-bridge.

why dont you order online ?

The gate logic seems ok, but you can't just drive a motor with logic gates (the transistors they are made of are really low power, just like a microcontroller's pin driving tranzistors)

What you need to do is turn 4 tranzistors on and off with the output of the logic gates. This may require a change in your logic circuit design, because you will probably have to use both PNP and NPN tranzistors and they are turned on differently. (PNP conduct when the base is connected to ground [ - ] and NPN conduct when the base is connected to [ + ])

I would suggest you read this http://www.mcmanis.com/chuck/robotics/tutorial/h-bridge/

This tutorial was the basis for my first H-Bridge and it worked perfectly.


Read the rules, R2-D2, thanks :)

Are you trying to use the 7400 chip to do PWM as shown on Dave Cook's Robot Room?

There are some practical limitations to this approach, as Dave points out in his article. You will need additional transistors to drive the motors, as others have pointed out.

You may want to try this out as a learning experience, but for practical use, you can build an h-bridge pretty easily.

The LMR H-Bridge Matrix provides a few practical examples, and a lot of good info on the subject.

Also, Dan M recently posted a practical and safe h-bridge design. He posts a variation here.

Dan M is cool..I like this bridge..

As everyone has pointed out, driving motors directly will be limited by the output of the logic chip. You seem to favor the 74xx chips but here are some 74x24x based motor drivers. Each leg can provide 35mA and can be stacked or used in parallel for more current. Chances are your geared motors will pull far more than is reasonable for these designs though. If you have specs for the motor it can help us (and you!) determine what is suitable for your needs.

Thanks to all of you guys.i wonder there is still so much to learn about a simple H bridge..