voltage regulators

[mateo88]

I believe you can drop up to 30 volts using an lm338, so yes, they will be perfectly fine. Just be sure to use heatsinks.

[moutoulos]

How much Ampere give LM338K in 30 Volt output (input 40 Volt) ?

[odysseybmx414]

thanks for all your help im going to go for the 338s then.

[mateo88]

Originally posted by moutoulos
How much Ampere give LM338K in 30 Volt output (input 40 Volt) ?

According to the datasheet, the lm338 has a 5 amp continuous output and can handle 12 amps for very short periods of time (like less than 0.1 seconds).

[moutoulos]

Originally posted by mateo88
According to the datasheet, the lm338 has a 5 amp continuous output and can handle 12 amps for very short periods of time (like less than 0.1 seconds).

Tnks very much .

[odysseybmx414]

but how to use lm338 with dual supply(+-V) not just a positive voltage but a negative voltage too?

[mateo88]

You have to use two of them, and run them in series. The point where they connect you use as ground. Nuuk's site has good information .

[odysseybmx414]

my trafo does not have dual secondaries it is a CT does the circuit change because of this or no?? sorry for so many questions

[mateo88]

I *think* you should be okay. A lot of CT transformers are really dual secondaries with the windings tied together anyway, so you might want to poke around a bit and see if that's the case. You can desolder the windings from each other and use them as dual secondaries, if you want. I really think you should be ok if you just connect negative to negative rail, positive to positive, and the center tap to the common leads on the lm338's.

[AndrewT]

Hi,
Mate88 in post8 gave some bad advice.

The point where they connect you use as ground.

No.

Connect the transformer centre tap to the smoothing capacitor common. connect a short wire from cap common to central star ground.

Do not connect anything else to the cap common.

Try to keep the routes from transformer to rectifier to cap to cap common to centre tap as ahort as practical. Also keep the area enclosed witin these loops as small as possible.