Motor Power Supply questions

[ravix]

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.

 

[k7elp60]

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.

 

[SixBullets]

regulated power supply not required

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

 

[ravix]

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.

 

[Hero999]

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.

 

[ravix]

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.

 

[Hero999]

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.