How does this work? (bipolar powersupply)

[joecool85]

Like the snubberized one used on the chipamp kits.

https://chipamp.com/images/ps.gif

How exactly does it make + and -? I understand that the power comes in off the transformer, goes through the diodes and gets converted to DC. However, both the top (+) and bottom (-) on the schematic look identical except for the resistor and cap at the end, is that what makes it + or - ?

 

[Nigel Goodwin]

Being positive or negative is simply a question of what it's related to - a DC supply has a positive and a negative, the negative is only negative in relation to the positive, and the positive is only positive in relation to the negative.

Unless you have some reference point positive and negative don't really exist.

 

[joecool85]

So, how does it make it negative in relation? Also, if you measure from ground to positive, you get 35volts, if you measure from ground to negative, get -35volts. Is it just the way the caps are put and stuff?

**edit**
I guess it has to do with the diodes. I tested before the caps and from where it goes to the bottom of the schematic it is negative. I just wonder how, since it seems identical to how the postive diode section is wired...

 

[Nigel Goodwin]

It's just like having two batteries, if you join the negative of one to the positive of the other, then read from the join - you get positive from one battery and negative from the other.

 

[joecool85]

Sort of... So how does that work with a ground? I mean, you could positive to ground and get a postive voltage, and negative to ground and get a negative reading...

 

[Nigel Goodwin]

Again, 'ground' is a purely arbitary point - YOU decide where you want 'ground' to be, and if it is actually connected to ground.

Back in the valve days 'ground' was usually the negative supply, but then in the early transistor days positive was more commonly 'ground' (as most transistors were PNP). As time progressed NPN transistors became more common, so now negative is usually used as 'ground'.

If you use split supplies (like opamps usually do), then the mid-point between the supplies is usually assigned as 'ground' - your supply diagram is basically intended as that, but can be connected in various ways as the two supplies are completely seperate.

 

[joecool85]

So, how would one split a batteries power into postive, ground and negative?

 

[Nigel Goodwin]

So, how would one split a batteries power into postive, ground and negative?

Two batteries!.

 

[joecool85]

How would that work?

+ 12v battery - + 12v battery -
pos ground neg

Would that work, and would it give +/-12?

 

[Nigel Goodwin]

How would that work?

+ 12v battery - + 12v battery -
pos ground neg

Would that work, and would it give +/-12?

Yes, that's how simple it is!.

 

[joecool85]

Wow, way cool. So I would need a DC->DC transformer or something to get +/- out of one battery right?

 

[akg]

Wow, way cool. So I would need a DC->DC transformer or something to get +/- out of one battery right?

 ------------------------------------ +
 |                  |
 |                  R
 |                  |
___               |
 --                 -------------------- gnd
 |                  |
 |                  R
 |                  |
 ------------------------------------- -ve

for low current this would suffice.

 

[Nigel Goodwin]

Wow, way cool. So I would need a DC->DC transformer or something to get +/- out of one battery right?

 ------------------------------------ +
 |                  |
 |                  R
 |                  |
___               |
 --                 -------------------- gnd
 |                  |
 |                  R
 |                  |
 ------------------------------------- -ve

for low current this would suffice.

Or for higher currents use an opamp, or an opamp and output transistors, all three of these are standard techniques.

However, they only give you plus/minus HALF the battery voltage.

 

[joecool85]

Right, so that would give me +/- 6v out of a 12v battery. Cool. I have no need for this right now, but its neat to learn.

 

[Nigel Goodwin]

Right, so that would give me +/- 6v out of a 12v battery. Cool. I have no need for this right now, but its neat to learn.

Bear in mind, it's dependent on fairly equal currents being drawn from the positive and negative rails!. It's commonly used for running opamps off a single supply.