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I have a simple circuit using an LM317-type voltage regulator (ZLDO1117GTA) as a constant-current source. The input is connected to a 15v source, and the output is charging a lead-acid battery.

In one mode, the output will be connected to the battery, but the 15v source will be disconnected. However, there will still be things connected to the 15v rail, so that needs to be at 0v.

Unfortunately, the behavior I'm getting is that power is backfeeding through the regulator's adjust pin and coming out the input, driving my 15v line high. How can I prevent this? Would a diode on the ADJ pin work?

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You need a diode to stop this .Its easiest to place the diode in series with the B pos output .If you use a schottky then the voltage wasted is not too bad .If you are worried about voltage drop then use a 40 Volt diode because it wastes less than say a 200 Volt type .

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