I'm putting a small H-bridge together using TIP121/126 to replace a SN754410NE. The schematic I'm following didn't list any values for the flyback diodes. In fact some examples left them out. I know that when this circuit is in use it switches from full forward to full reverse with no ramping. This tends to overheat the SN754410NE with small motors and blow it with motors slightly larger.
The H-Bridge is driven by a LM339 and about the only adjustment I have is the amount of deadband between directions. My question is how to determine values for the flyback diodes. In the past I used the motor stall current spec to be on the safe side. In other circuits I often see very small diodes like 1A on a 7A drive. Also voltage rating, does the back EMF rise much greater than the supply voltage? If so how much higher % should one use? Since someone will ask - this is the ram servo control for a small tabletop sinker EDM - the abrupt movements really aid in flushing as well as breaking momentary shorts sometimes caused by debris in the work contact area. Thanks much team. Greg ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
