So I made this little boost regulator for powering 12V LED bulbs:
And I followed the datasheet exactly: http://www.ti.com/lit/ds/symlink/lm27313.pdf
And it seemed to work perfectly fine. I only just recently noticed however that it's not working as expected at all. It will output 12v when the SHDN pin is pulled high, but when it's pulled low, the module outputs 5V, when I expected it to output 0V. I mean, typically that's what a shutdown pin is for on a regulator right? To make it stop outputting?
The reason I hadn't noticed this before now is thankfully most 12V LED bulbs won't light if powered by 5V. I'm not sure if they're still drawing power or not, but at least the board works for its intended application. I did notice that some bulbs light with 9V though, and I recently ordered some even smaller bulbs which I hope do not light with 5V or that is going to be a costly mistake.
Anyway, I suspect that the 5V is just flowing straight through that inductor, since it goes right from the 5V input pin to the output side of the regulator. But that's how it was wired up in the datasheet, so I'm confused why they even have the shutdown pin wired up there if all that is ever going to do is take the regulator from 12V down to Vin.
It seems like if I want this regulator to function the way I want it would require a complete redesign, with a new regulator, or by adding a mosfet in there to actually work as a proper shutdown pin.
So, what are your thoughts on this? Is the board functioning properly as designed in their schematic? Is there an easy fix without adding a mosfet? And what is that shutdown pin really for?
I guess what the pin is really for is this: "This part has a logic-level shutdown pin that can be used to reduce quiescent current and extend battery life."
But it still does not make sense why one would want to reduce the output from 12v to 5v instead of reducing it to 0v, if the goal is to save power.