LM350 Voltage Regulator Kit

Huhhhh...

The adjustment pin current max draw is 100uA max.

The reference voltage is 1.262V max.

| R2 low | |

Assuming R1 and R2 are not part of any necessary minimal loading..

How about pick a 10x swamping current through R1 and R2.

P =(12V-1.262V)*1mA = 10mW R2

P =1.262V * 1mA = 1.2mW R1

Use 1/4W resistors :P

It'll take me longer to figure out how low the current can be through R1 and R2.

D from BC

They are just programming resistors, with high enough resistance that they pull neglible current.

But you know, have you considered learning switching supplies? (instead of linear). Pretty soon, you won't even be able to sell linear widgets in California (USA) The problem is they waste power due to their inherent low efficiency. Note: Several power-plant's worth with enough linear devices considered!!!

So why not bite the bullet and tackle a switching design? I suggest the LM25576, which you can design online here:

If you can settle for 1-amp (instead of 3A output), the LM2575T is a very simple design. For 12 volts, they even have one that has the programming resisitors already set inside the package. But for the variable one, you would still add the 2 programming resistors as above.

Anyway, I think the LM2575T is ideal if you want to learn about switching supplies. At 52 kHz, it's easy enough to scope, and layout on a PCB without too much noise trouble. You'll need a coil and a couple filter caps. And a fast Shottkey diode, but that's about it.

Good luck.

-mpm

That's the min load current spec = 10mA. :P I think that's to provide best internal bias levels within the LM150.

That doesn't mean the min current through R1 and R2. If there's a load >=10mA, then the sense resistors don't have to be part of the min loading and can draw less current.

D from BC