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[SOLVED] Bench PSU Project - should I use two rectifiers/transformers?

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SparkyBoy

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Require:

-5v 0v +5v
-12v 0v +12v

and

0v 24v

Want to use 78/79 regulators & L200 reg.

Should I use two rectifiers, one for dual rail one for single rail?

Should I use two transformers?

Can I tie all 0v together to form common ground ref.?

Will a 28v secondary voltage (for the 24v supply) over heat a 78/79 regulator?

Have lots of examples of single or dualrails supplies but not both together?

Thanks

Mark
 

SparkyBoy said:
Require:

-5v 0v +5v
-12v 0v +12v

and

0v 24v

Want to use 78/79 regulators & L200 reg.

Should I use two rectifiers, one for dual rail one for single rail?

Should I use two transformers?

Can I tie all 0v together to form common ground ref.?

Will a 28v secondary voltage (for the 24v supply) over heat a 78/79 regulator?

Have lots of examples of single or dualrails supplies but not both together?

Thanks

Mark
Click to expand...


First, lets start with two transformers issue ..
If you can't find suitable multi-tap transformer (it can be CT or independent windings) then using several smaller transformer instead is not a problem ..

These voltage regulators will generate a lot of heat only when you draw a lot of current and the input-output voltage gap is wide ..
In any case, using 28Vdc to step down to 5Vdc is rather not a good idea ..
Much better option is working with much lower unregulated voltage, perhaps somewhere around 9Vdc ..

You can tie all 0V together but that may depend whether you use CT (centre-tap) configuration with 0V already defined or independent windings and full bridge rectifiers ..

See attached picture ..

IanP
:wink:
 

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IanP said:
See attached picture ..
Click to expand...

Hi IanP
Thanks for replying..

I will probably go for 2 transformers, a smaller transformer for the 5v side. My enclosure will probably not cater for three unfortunatley.

One question though is on the picture what is the purpose of R1 before U5? Does it work with Cap(s) (CR) to delay/smooth power up?

Regards

Mark
 

One question though is on the picture what is the purpose of R1 before U5? Does it work with Cap(s) (CR) to delay/smooth power up?
Click to expand...
This PS was originally used in an audio amplifier ..
The voltage that feeds U5 is quite high (32V or-something), so I think someone decided to use 12ohm resistor to drop the voltage down and possibly to delay the voltage, too .. ..
If you choose proper transformers the input voltages for voltage regulators will not be that high, and I wouldn't even think about resistors ..
Just make sure that you use decent heatsinks or maybe small fan(s) ..

IanP
:wink:
 

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