I'm building an H-Bridge to drive some motors I have around. I'd like to have a bridge that can be powered by different power sources, for example batteries or atx power supplies interchangeably.
I've attached a common schematic. Let's say transistors Q4 and Q1 are ON, so that the motor is spinning. If the transistors go OFF, then the back-emf of the motor will cause a current to flow from GND to the supply through D4 and D1. Am I right?
The problem is, I don't want the power supply to sink current. Maybe a battery can handle this current without any danger, but what about a generic SMPS?
A possible solution I've come across is the use of a sort of "shutdown phase". Doing so, the current flowing in the flyback diodes is kept in the h-bridge and doesn't go into the supply. As before, let's suppose that Q4 and Q1 are conducting. Instead of switching off them together, I switch off only Q1, and let the freewheeling current flow between Q4 and D1. Only after, Q4 is shut down too. Does this make sense?
If yes, could you suggest me how much time the "shutdown phase" could take? I mean, how can I figure out how long does it take to "discharge" the back emf of the motor?
Thanks, any help would be appreciated!