Hey everyone, I recently built an H-bridge with four darlington pairs being fed by PWM from a pic. I have two questions/concerns:

1.) Is it possible to run both an H-bridge and a motor from the same power source without significant interference on the logic side? I'd like to run the h-bridge at 12v, then use a voltage regulator to supply 5v to the PIC. Can a regulator provide clean and stable enough power from the noisy h-bridge circuit?

2.) I built an LM317 based bench power supply to use for projects like this. However, when I use it to supply motors the performance of the motor degrades over the first minute or so and often stops. Can LM317 based power supplies be used for small motors? I also notice it sometimes acts funny when supply circuits with large capacitors.

The LM317 is kept very cool (large heatsink with fan) and the motor doesn't draw more than 1 amp.

Right now I am running my motor with a 9v battery and it works better than the PSU.

 

If you post the circuits that you are using perhaps we can help you.
Even with a power supply extra filtering is sometimes required for loads on the power supply, such as a motor. If the motor has brushes the noise generated by the brushes can cause the 317 to malfunction. A electrolytic capacitor near the motor terminals may help but it can cause surge current problems with the 317 if a protection diode is not used.

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Hi,
I dont understand why u need regulated supply when u have a PWM controlled H bridge

 

The power supply powered the entire circuit, working with a transformer and rectifier to bring the mains voltage down to a more reasonable 12v DC.


Since someone brought this topic back, I might as well let everyone know what I discovered.

The motor was drawing WAY more current than I thought. I used to think that the lm317 would just turn off if I tried to draw too much current, when in reality it just limits the voltage at the output.

So when I hookup up the motor it worked fine for the first few seconds but slowly degraded in performance as the 317 lowered the output voltage to protect itself.

 

Whay not just use the non regulated output directly from the filter capacitor to power the h-bridge?

Motors aren't bothered about voltage regulation, in fact it's probably better to use the non-regulated supply because the regulator will stop some of the noise generated by the motor from affecting the rest of the circuit.

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The transformer I have brings the mains voltage down to ~25v, I was using the regulator to bring it from there down to 12v.

Anyway, I got the circuit working, I just had to use a different power supply that could provide more current.

 

You could easilly run it at 25V, if you're worried about overloading it, then never run the PWM at more than 50% duty cycle.

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