ac to dc power supply

[Serpent]

to put frankly, im a sorta-beginner when it comes to electronics
my problem is that a circuit i found in a book is for an ac to dc
power supply..the setup is relatively simple, and winds up with 3
outputs (+, -, and ground, although not an output) with two
potentiometers leading to the pos. and neg. output..
my question is why the circuit would require two potentiometers to
control the flow..it seems to me like the circuit should have one
potentiometer attached to the neg. output..

sorry if the question is unanswerable without seeing the circuit, im
tryin to setup my scanner to help work around that

thanks for any response

 

[Active8]

You are looking at a schematic for a dual power supply. It just happens
that ground is the common lead, which is the most likely situation. Now, since
you have two separate voltages, it only stands to reason that if both are
adjustable, they each need a potentiometer or other control device.
One control will set the voltage of the positive supply, the other will
control the negative supply.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip

in that case, if it's just a xfmr/rectifier/filter/pot, he's also
looking at a (IMHO) crap design since the pots are probably large value
(Rpot >> Rl) and the open circuit voltage will no doubt be greater than
the closed circuit voltage. changing load currents - say he closes the
switch on a high current load - will change the output. fast changing
loads, assuming a constant Irms, could be dealt with using ample
filtering, which is part of regulation anyway. but if he wants a bench
supply, why deal with worrying about what the voltage is going to be
when under load - you know - turn down the pot, connect the load, crank
it up while watching the meter...

i would use an adjustable LM117/LM317 regulator. for extra current, use
a boosting transistor. maybe a LM317 referenced series pass regulator
would do the trick.

mmm ... [quick check] ... then we have the LM150(3A) and LM138(5A) regs.
and the LM137 negative reg.

mike

 

[Sir Charles W. Shults III]

in that case, if it's just a xfmr/rectifier/filter/pot, he's also
looking at a (IMHO) crap design since the pots are probably large value
(Rpot >> Rl) and the open circuit voltage will no doubt be greater than
the closed circuit voltage. changing load currents - say he closes the

i would use an adjustable LM117/LM317 regulator. for extra current, use
a boosting transistor. maybe a LM317 referenced series pass regulator
would do the trick.

mmm ... [quick check] ... then we have the LM150(3A) and LM138(5A) regs.
and the LM137 negative reg.

mike

Absolutely nothing was posted about the design other than it had
potentiometers that led from the outputs. We don't know if it is regulated or
not. It may well have LM317/LM137 style regulators, and note that he originally
called the common an output. In this case, the potentiometers would be from
ground to the common terminal of the regulator chip, (if it was made using the
simplest schematic on the LM317 slash sheet), and he would have stated that the
potentiometers were wired to the output.
Based on what he originally posted, we cannot say whether it is regulated or
not- his original error obscures a piece of information that might have told us.
Not surprising considering that he stated he was a newbie.

Cheers!

Chip Shults
My robotics, space and CGI web page - http://home.cfl.rr.com/aichip