# Advice needed: LM340K-5.0 source or substitute

#### metermannd

Joined Oct 25, 2020
334
I have a circuit that has a heavy-duty 5V regulator (LM340K-5.0 to be precise, the LM309K is probably an equivalent).

As I'm considering reproducing / simplifying the original, I've hit a stumbling block with the regulator. Seems all the reputable sources (Digi-Key et al) all want to charge over $50 for ONE, and which makes the project unfeasible... I see some are available for less than$10, but I don't want to get rooked with a possibly counterfeit part.

I don't know for sure yet exactly much regulator I DO need (but two 12V supplies exist on the board, presenting a possibility of splitting the 5V load), but just wanted to see if anyone else ran into this and what, if any, solution they chose.

Thoughts?

#### MrSalts

Joined Apr 2, 2020
2,622
Get a smps module that can take 12VDC input and be set to 5v output. Handle up to 5 amps. 80 to 90% efficient so little heat.

The linear LM350 uses a method to simply convert the excess voltage x drawn current to heat. Essentially 0% efficient.

#### metermannd

Joined Oct 25, 2020
334
That part should work out fine, and price is VERY reasonable. Appreciate the suggestion.

I'm down to picking out footprints for the last few parts (using KiCAD) so I could just drop that right into the schematic and free up the space the heatsink would consume otherwise. I may be interested in the breakout board regardless.

Relevant portion of schematic attached (with the LM340K-5 still present)

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#### MrSalts

Joined Apr 2, 2020
2,622
You'll need to connect the voltage programming pin to ground with the correct resistor to get a 5v output. See the last page of the datasheet. Or, I can tack it in place if you need a 0.1" offset breakout board.

#### metermannd

Joined Oct 25, 2020
334

#### MrSalts

Joined Apr 2, 2020
2,622
It has a maximum of 1.5A. If that is enough, it is a perfectly fine option.