Thursday, 30 April 2015

Is it safe to bypass an LDO by shorting its input and output?


I am making a programming adapter that will deliver 5V or 3,3V to the target board. I want to use a simple DIP switch to select voltage (I know that an SPDT is the canonical way).


Is it safe to short the input and output of an LDO like LD1117. Internal schematic is on page 3 of the datasheet.



Answer




As far as I know this is actually a fairly common solution. I know I've used this setup in the past without any problems.


This application note from LT even shows how to do this automatically, using a FET as the bridge: 5V to 3.3V Regulator with Fail-Safe Switchover – Design Note 82.


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