Raising output voltage of LM74M05CT with a diode on ground?

Something is not quite right in the details. The 78m05 500mA shouldn't provide 1 amp, but even if it did, your 2 foot wire resistance would have to be .5 ohms to drop .5 volts at 1 amp. That's not a reasonable number. Maybe there are connectors involved?

Anyway, your proposed solution should work well for what you described. But read on, there's a caveat below.

The last sentence above is a puzzler. Are you saying that if the output rises to the supply voltage that's not a problem?

Ed

Yeah, 78M05 - 500mA, oops!

I should have proof read that post better - and sorry about the double post!

My thought was using a resistor or germanium diode runs the risk of an open circuit on the ground leg - and I expect that the output voltage could then float to be close to the input voltage. Whereas a silicon diode normally shorts which would then only drop the Vcc to the original

Thanks everyone!

John :-#)#

Circuit concerns identical to ehsjr's went through my own mind. Thank you for clarifying your typos and sharing your invaluable insights into the common component failure modes that you experienced over your career.

Based on your description of your customers, it seems like the most likely failure mode would be your customers' soldering being unreliable or incorrect in the first place.

If the diode works perfectly, but one of its connections comes loose due to bad soldering, it is still likely that the output will rise and blow up something. Certainly having the minimum number of components is a good start though.

I'd be more concerned about a cold solder joint or some flexing of the PCB (removing/installing or mating connectors) causing a joint to open.

Actually, since I started this thread I figured out a better solution to the problem.

This advice is no longer required, but is useful none the less.

Thanks!

John :-#)#

Not all 78M05 are created equal. The Fairchild version is 1 Amp. And the OP works with "lagacy/vintage" equipment? But you're right about the wire drop. Even 22ga 2ft is only 32mV at 1A, 64mV round trip, which shouldn't make any difference for a logic board.