PS Regulator

[freezer]

I have a 12-0-12 10A transformer and would like to build a 24v ps. I figure that I will have about 34vdc unregulated and was going to make a regulator curcit. I was looking at the LM338 datasheet but the op amp is not available anymore. Anyone have an upto date schematic/parts for a 24v and 5v out put?

Thx,
Rod

[Al_The_Man]

Rod, I see stock LM338 at Digi-Key 1777 pieces, they specialize in mail order.
Al

[pminmo]

LM338's are still available, You could goto a newer low dropout regulator such as the LMS1585ACT-ADJ from National and put a series resistor to drop some of the voltage to minimize package disipation. Or you could use a seperaate regulator for each motor. I've done business with Futurlec on the web. They show the 338K but they take a couple of weeks to get usually.

http://www.futurlec.com/ICLinearRegulators.shtml

[pminmo]

Digikey also has:
http://www.digikey.com/scripts/DkSea...S&Cat=31589511

[abasir]

Just bear in mind that the regulator would have to dissipate about 100W of heat (34V-24V)x(10A)=100W.

Why not get a new transformer (18V@10A) to avoid using the regulator alltogether?

[pminmo]

Originally posted by abasir Just bear in mind that the regulator would have to dissipate about 100W of heat (34V-24V)x(10A)=100W. Why not get a new transformer (18V@10A) to avoid using the regulator alltogether?

Actually buy the time he gets it rectified it will be closer to 31V under load. But your correct on the dissipation if he were to get a single regulator, but the 338 is a 5A max regulator for 35 watts, still a bunch of heat. Need a good heatsink. Some 5 6A diodes in series would drop around 4.5v at 5 A. Or a 25W 1ohm resistor.

[ballendo]

Hello,


Not really answering your question, but:

Why are you regulating the supply?

What are you using it for?

Because there are very few places in CNC where a 34v supply would need to be regulated...

Thank you in advance

Ballendo

[freezer]

It is the op amp in the design sheet for a 15A var regulator that is not available anymore... I think it is the LM307 but not 100% sure without getting the datasheet out...

Just had the 12-0-12 10a transformer and thought i could regulate it cheeper than buying a new transformer. It is just to hook to my new xylotex 3axis board that is in the mail... Jeff thinks that with higher line voltage the transformer will be doing more like 35vdc (the max for the board).

I am also having trouble finding a cheap place to get 34000uf+/- cap. That is what you need for a 10A 24v supply if i remember correctly (it is 80000*I/V)...

You are probably correct... it will be eaiser to just get a 18v 10A transformer...

[ballendo]

Freezer,

Thank you for the reply. Now it makes sense.

Just an FYI, the guys at DenverCNC tested a xylotex board running the max (3 steppers at 2-1/2A).

They found that a 4.2A supply was plenty big enough. Thought you might like to know

Ballendo

P.S. A lot of guys with xylo's are using surplus switching power supplies. 24 and 24.5V at about 6A seem to be available at a cheap price-- about 30 bucks.