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Two power supply schematics

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Cobalt60

New Member
Hello. I am trying to understand a few different power supply designs. I have included 2 schematics which I have found on the web.

The first I think is a typical "uni-polar" design, is this correct?

The second I think is a typical "bi-polar" design, is this correct?

Basically, I am trying to design a power supply. I think a good starting point is to figure out what its basic design is going to be. If I did indeed correctly identify these 2 diagrams as uni-polar and bi-polar ones, Id like to know the advantages and disadvantages of each design.

Thanks

-Chris P
 

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crutschow

Well-Known Member
Most Helpful Member
The first supply has one output voltage. It is used to power circuits, such as digital, which require only one supply.

The second generates a plus output voltage and a minus output voltage. It can be used to power circuits that use a single supply voltage (using only one output), or both a plus and minus voltage, which some analog circuits require.

Obviously the dual output supply is more versatile since it can power circuits that require either a single voltage or a plus and minus voltage.

For my own bench supply I built two isolated single supplies in the same box. That way it can be used as a dual plus and minus supply or a dual supply with two different positive (or negative) voltages as desired. This works since isolated supplies can have either their positive or negative outputs connected to circuit ground as needed.
 

Cobalt60

New Member
On the second schematic, could you use the negative as ground, in an attempt to get a greater positive voltage than using just one regulator and ground?

Carl, you suggest a good alternative would be to make 2 uni-polar supplies in one unit? So to achieve a negative voltage, you would hook the positive to the ground of your circuit, and the ground to the negative of your circuit? What did you do for efficiency of your supply? I was thinking to use a variac instead of a fixed transformer to minimize voltage drop.
 

Neal

Member
Tne unipolar power supply has an error on the bridge rectifier. See my attachment. The diode with the red circle needs to be reversed.
A normal unipolar power supply has on one output voltage. The bipolar has two which is an advantage
The diode is NOT reversed, is correct the way it was drawn.
 

mark_3094

New Member
Is the first circuit a real circuit (minus the component values), or is a 'conceptual' circuit?
That is, could some values be added to the circuit components, and that is all that is needed to be done?
 

crutschow

Well-Known Member
Most Helpful Member
On the second schematic, could you use the negative as ground, in an attempt to get a greater positive voltage than using just one regulator and ground?
Yes you can.
Carl, you suggest a good alternative would be to make 2 uni-polar supplies in one unit? So to achieve a negative voltage, you would hook the positive to the ground of your circuit, and the ground to the negative of your circuit? What did you do for efficiency of your supply? I was thinking to use a variac instead of a fixed transformer to minimize voltage drop.
You just make two duplicate uni-polar supplies with a transformer that has two isolated identical output windings.

My supply has a max output of 1A at 30V so efficiency was not a big concern. The transformer I used did have a 110/220V split input winding so I connected that to a switch to give 1/2 voltage on the output when I needed 15V or less on the output (my lines are 110v). That reduced the power dissipation for lower output voltages. You could also use a variac at the input to your power transformer.
 

Torben

Well-Known Member
Is the first circuit a real circuit (minus the component values), or is a 'conceptual' circuit?
That is, could some values be added to the circuit components, and that is all that is needed to be done?
I'd call it "conceptual, but. . ." :). All the major players are there, but without specifying the 3-terminal regulator it's impossible to say. For instance, 78xx regulators like to have a couple of caps on them to handle transients and prevent oscillation. Others may have other requirements.

Plus, I'd really want to put a fuse on it, and a switch, and a cap on the AC side (but I'm a bit fuzzy on that bit since you'd need to calculate it to avoid resonance with the transformer, or so I'm told).

That said, if you pulled off the regulator, it's essentially what you'll find inside a wall wart. So in that sense, yes, it's a complete linear power supply schematic, but it needs a few more bits to make it a decent one.

My usual disclaimer: I'm a hobbyist (read: just some yahoo with a soldering iron). If I'm leading you down the garden path I hope to be corrected by one of our resident experts. But I have built a few linear supplies. The early ones resembled the first schematic shown here. And all of them contain at least those stages (stepdown transformer, rectification, filtering, regulation).

It really depends on what you need it to do and what sort of specs and performance you want to see out of it.


Torben
 
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k7elp60

Active Member
The diode is NOT reversed, is correct the way it was drawn.
You are correct.
Please forgive me for my error.
I have deleted my original post
.
 
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