I this power supply good?

[little billy]

Hello,

Is the following psu any good

http://www.redcircuits.com/Page36.htm

The voltage reference is taken from the output,
wouldn't it have made more sense to had some sort
of zener diode reference, I mean, any input ripple
is going to be present in the output, and worse still
it will be amplified by Q1 so the output ripple
will be even worse than the input ripple. This
circuit is bad, isn't it?

 

[John Popelish]

little billy wrote:

Hello,

Is the following psu any good

Define good. It probably works for some things and is certainly
simple ot make. It is not as good as a lab grade adjustable supply
that costs a hundred bucks or so.

http://www.redcircuits.com/Page36.htm

The voltage reference is taken from the output,
wouldn't it have made more sense to had some sort
of zener diode reference, I mean, any input ripple
is going to be present in the output, and worse still
it will be amplified by Q1 so the output ripple
will be even worse than the input ripple. This
circuit is bad, isn't it?

You should think of this circuit as using the turn on voltage of a
transistor as its reference (both for the voltage setpoint and the
current limit). Of course this is not a very sharp or temperature
stable reference, but it may serve your purposes, which I am not aware
of.

--
John Popelish

 

[little billy]

I think I was wrong about this circuit. It is alright. What sort of
ripple can I expect to get at the output compared to the input, i.e.
by how much will the ripple be reduced, and how does that compare with
a proper laboratory regulated power supplies ?

p.s.
Did you see my other power supply question a few postings before,
what's your take on R7, why is it 220R, what does it do ?

 

[John Popelish]

little billy wrote:

I think I was wrong about this circuit. It is alright. What sort of
ripple can I expect to get at the output compared to the input, i.e.
by how much will the ripple be reduced, and how does that compare with
a proper laboratory regulated power supplies ?

Without some calculation or a simulation, I can't say. The reduction
ratio is approximately equal to the voltage gain around the control
loop at the ripple frequency. This one is simple enough to easily be
put into LTspice with an input consisting of an AC ripple voltage
riding on a DC bias.

You can download a free copy of LTspice at:
http://www.linear.com/software/

p.s.
Did you see my other power supply question a few postings before,
what's your take on R7, why is it 220R, what does it do ?

Sorry, I didn't take the time to think through how that circuit works.

--
John Popelish

 

[Rich Grise]

little billy wrote:

Hello,

Is the following psu any good

http://www.redcircuits.com/Page36.htm

The voltage reference is taken from the output,
wouldn't it have made more sense to had some sort
of zener diode reference, I mean, any input ripple
is going to be present in the output, and worse still
it will be amplified by Q1 so the output ripple
will be even worse than the input ripple. This
circuit is bad, isn't it?

It's adjustable. You turn the knob and use a meter to
tell you if it's the voltage you want.

Hope This Helps!
Rich

 

[little billy]

Hi again,

John Popelish <jpopelish@rica.net> wrote in message news:<410FB0B3.3B608209@rica.net>...

little billy wrote:

I think I was wrong about this circuit. It is alright. What sort of
ripple can I expect to get at the output compared to the input, i.e.
by how much will the ripple be reduced, and how does that compare with
a proper laboratory regulated power supplies ?

Without some calculation or a simulation, I can't say. The reduction
ratio is approximately equal to the voltage gain around the control
loop at the ripple frequency. This one is simple enough to easily be
put into LTspice with an input consisting of an AC ripple voltage
riding on a DC bias.

You can download a free copy of LTspice at:
http://www.linear.com/software/

It seems that the output ripple is almost as bad as the input ripple,
take a look at my simulation results

http://uk.geocities.com/lklkjjlkjklj@btinternet.com/sim1.gif

Either something is wrong, or this circuit goes to the bin.

??

p.s.
Did you see my other power supply question a few postings before,
what's your take on R7, why is it 220R, what does it do ?

Sorry, I didn't take the time to think through how that circuit works.