Question about regulated PSU by CarlosFM.

[blackboy]

Hi guys, I have a PSU which has only 30-0-30 (3 terminals), is it possible to build the Carlos' regulated PSU? if yes, what is the schematic?? and one more question, how many uf of capacitance is necessary for 3886GC before lm338?? Thx!!

[gootee]

Originally posted by blackboy
Hi guys, I have a PSU which has only 30-0-30 (3 terminals), is it possible to build the Carlos' regulated PSU? if yes, what is the schematic?? and one more question, how many uf of capacitance is necessary for 3886GC before lm338?? Thx!!

I don't think it's possible, without two separate transformers.

- Tom Gootee

http://www.fullnet.com/~tomg/index.html

-

[Archwn]

use only 4 rectifier diodes instead of 8 and you will get what you want.

hint: a ground is a ground.

[AndrewT]

hint: a ground is a ground.

that is just the start of more confusion.
Most "grounds" do different jobs and we could champion the cause of clarity if we used different names for each different use.
eg, safety earth,
return,
zero volt reference,
PSU power zero volts.
common,
etc.

Often, these are combined, but that combination should be the result of deliberate thought by the designer and not an accident because everyone called them "ground".

[AndrewT]

I have a PSU which has only 30-0-30 (3 terminals)

build the Carlos' regulated PSU?

the Carlos' power regulator uses positive chip regs. This requires a pair of isolated inputs to each regulator. The zero volt line after the regulators becomes the power ground. The four inputs must ALL be isolated from the power ground and from each other.

A three input PSU cannot meet this requirement.

[neeraj]

Hi,
i have 2 nos Toroidl trafos 35-0-35 , 225 VA rating.
Can i use these trafos with chip LM 3886?
What are the necessary requirements to bring down the out put voltage to 30-0-30 volt after rectification?
Regulated power supply is another option which is also suitable for the same.
Plz guide.

[AndrewT]

Hi Neeraj,
the voltage is too high.
The DC will be in excess of 50V.
Dropping that to +-35Vdc (for 8ohm) results in 15V*2.2A= 33Watts of maximum dissipation for each polarity.

[jackinnj]

Originally posted by neeraj
Hi,
i have 2 nos Toroidl trafos 35-0-35 , 225 VA rating.
Can i use these trafos with chip LM 3886?

By itself, no -- the max operating voltage of the LM3875 is 42 volts each side for an 8 ohm load. If you have a 4 ohm load it is much lower.

Don't forget that you can unwind a few turns of the transformer to attain lower voltage.

[AndrewT]

you can unwind a few turns of the transformer to attain lower voltage

but that reduces the VA rating in direct proportion to the voltage reduction.

[jackinnj]

Originally posted by AndrewT
but that reduces the VA rating in direct proportion to the voltage reduction.

Isn't the current a function of the BH character of the core?