Power supply for DC motors

[dmta]

Hi all,

I need a variable power supply to control 2 H bridges which drive 2 DC motors. The max output current and voltage is 5A and 20V respectively. I have designed the following circuit based on Dave Jones's lab supply where the output voltage and current is set by filtered PWM signals.

What can I do to improve the stability and quality on this design? Can someone recommend a better power transistor for this as I find it a little hard to choose one. Your input will be most valuable.

Regards

 

[alec_t]

What can I do to improve the stability and quality on this design?

Why are Q2/Q3 there? They form a quasi-constant current load of ~17mA, but that is subject to drift because of the change of Q3's Vbe with temperature. If you really want a constant load current there would be better ways to do it.

 

[ronv]

You need to be careful driving motors with a supply like this. If you reverse the motor before it has stopped the generator action will raise the supply voltage.