Need help with H-bridge

chronister

Hello. I'm trying to design an H-bridge circuit to use to control a large motor. I'd like advice on whether or not this design will work before I build it. The schematic is here:

http://www.ornithopter.org/hbridge.gif

The components I plan to use are two P-channel MOSFETS (P1 and P2 in the schematic), two N-channel MOSFETS (N1 and N2), four schottky diodes, four 100K pull-down resistors to prevent static electricity from turning on the MOSFETS, and two 1K resistors on the inputs to protect the microcontroller.

I wasn't sure where to put the pull-down resistors for the P-channel MOSFETS. Could you please let me know if this is right?

Also, is there some way I can implement a brake, and what changes would that require?

Thanks for your comments. If this gets the approval then hopefully it will be of use to others who may be looking for a simple H-bridge circuit.

Nathan<!-- Edit -->

Post Edited By Moderator (Jon Williams) : 12/12/2004 3:53:53 AM GMT

Minikraut

Have a look at The Robot Store site. There I found a 10 Amp, Dual H-bridge which you can buy for around $60. They also provide a full schematic and parts list. This one uses a simple 74HCT139 as a decoder to properly gate the correct Mosfets through opto-isolators for forward, rev, and brake. Should not be that difficult to build from the schematic.

Good luck

Hal

stamptrol

·· The circuit should work fine. The two resistors R1, R2 are the "pull-downs" for the P-channel devices. A P-chan turns 'ON' when the gate is low. Therefore, when it is held high (by R1, R2) the devices are biased OFF.

·· Take careful note that the two inputs should NEVER be HIGH at the same instant, otherwise you'll have a dead short from +9 to GND. For instance, IN1 high and in2 low might give Clockwise rotation, IN1 low and IN2 High would then give counter-clockwise rotation.

· Choose MOSFETS with low gate voltage requirements. For instance use IRL520's for the N-channels and their complements for the P-Channels.

· For braking, suppose In1 is HIGH and IN2 is LOW and the motor is running. To quickly stop the motor, momentarily put the inputs in the opposite states to give the motor a shot of reverse voltage. Then turn both inputs OFF. With the right length of reverse voltage, the motor will come to a stop just as the inputs both get turned OFF.

· Tom

chronister

Thanks for your suggestions. I checked out the controller at Robot Store. It looks like it would be useful for me, except for the fact that I am forced to minimize weight. Therefore I'll need to give up some of the nice features that unit has.

Nathan

Guenther Daubach

Nathan,

I have been using the L6203 DMOS full H-Bridge drivers manufactured by ST for one of my SX-based projects with great success.

See http://www.parallax.com/sx/projects/projects_pwm.asp for a description of this project.

ST also offers other H-Bridge modules capable of higher currents as well.

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Greetings from Germany,


G