Can someone explain to me how negative voltage works?

[Eli]

In the context of power supplies...

Most people here will only be familiar with computer power supplies, so that's fine. But any power supply really... I've been searching for a good bench supply lately, and I see a lot of power supplies that have negative voltage outputs.

What use is it?

I can conceptualize positive DC voltage easily, but.. I dun get the negative sh!t. What is happening when you connect a load between say, -12VDC and ground?

If I connect a 12V lightbulb to -12V and ground on a computer power supply, will the bulb experience negative voltage, implode, and cause a rift in the space time continuum?

:Q

lol

 

[quakefiend420]

Originally posted by: Eli


If I connect a 12V lightbulb to -12V and ground on a computer power supply, will the bulb experience negative voltage, implode, and cause a rift in the space time continuum?

:Q

lol

yes

 

[SynthDude2001]

I probably could have answered this a year and a half ago when I was in my Electricity and Optics class, but alas I have all but forgotten that which I used to know.

 

[95SS]

My brain hurts just trying to imagine this. Link to said bench power supplies?

 

[Batti]

The only thing required is a difference in potential. There's still a 12V potential across the lightbulb, so it will light. The bulb doesn't care which way the current is flowing.

+ and - supplies are often used in amplifiers, where you really want the output to be able to swing 24V.

 

[Eli]

Originally posted by: 95SS
My brain hurts just trying to imagine this. Link to said bench power supplies?

lemme find a good one, but.. just think about your power supply.

It has:

+12v
+5v
+3.3v
-12v
-5v
0v(ground)

Ok.

So if you hook a fan up to +12V and ground, there is a difference of 12v(0 - 12 = 12V).

If you hook the fan up between +12v and -5v, there is a difference of 17v(+12 - -5 = 17V)

Right?

I'm still having trouble visualizing it though. Can you actually power a load with the -12v line? What is it for in the case of a computer power supply?

If you hook -12v up to ground... Don't you still get 12 volts? (0 - -12 = 12)?

Ok, I guess I answered my own question.

So for all practical purposes, is a negative output just as useful as a "regular" one? What's the point!? lol

Just so you can easily make different voltages within the circuitry?

 

[95SS]

Makes sense, as does what Batti said. It's too late to think straight. Plus, electronics was never my strong suit. Batti, is that what is referred to as a switching power supply?

 

[DivideBYZero]

Originally posted by: Eli

Originally posted by: 95SS
My brain hurts just trying to imagine this. Link to said bench power supplies?

lemme find a good one, but.. just think about your power supply.

It has:

+12v
+5v
+3.3v
-12v
-5v
0v(ground)

Ok.

So if you hook a fan up to +12V and ground, there is a difference of 12v(0 - 12 = 12V).

If you hook the fan up between +12v and -5v, there is a difference of 17v(+12 - -5 = 17V)

Right?

I'm still having trouble visualizing it though. Can you actually power a load with the -12v line? What is it for in the case of a computer power supply?

If you hook -12v up to ground... Don't you still get 12 volts? (0 - -12 = 12)?

Ok, I guess I answered my own question.

So for all practical purposes, is a negative output just as useful as a "regular" one? What's the point!? lol

Just so you can easily make different voltages within the circuitry?

Thats about right. To 7 volt a Fan, to make it quiet, you attach the +12 and the +5.

 

[Oger]

Eli;

You are associating positve voltage (potential energy) with the absence of electrons in a circuit (negative voltage).

Look at it this way, postive voltage is electron flow, negative voltage is how a circuit reacts to electron flow.

12 +

5 -

= 7 volts.

In this equation the 12 V circuit is not connected to ground directly but through a 5 V out of phase bus thus the load sees 7 V positive.

 

[Analog]

Positive supplies push currrent.

Negative supplies SUCK current.

'nuf said?

 

[JW310]

Originally posted by: Oger
Eli;

You are associating positve voltage (potential energy) with the absence of electrons in a circuit (negative voltage).

Look at it this way, postive voltage is electron flow, negative voltage is how a circuit reacts to electron flow.

12 +

5 -

= 7 volts.

In this equation the 12 V circuit is not connected to ground directly but through a 5 V out of phase bus thus the load sees 7 V positive.

No... if you were to hook something up to the +12 and -5 volt leads on a power supply, the device would see +17 volts, not +7 volts. The voltage it would see is the difference between the two voltages. If you hooked it up to +12 and +5, then the device would receive +7 volts.

In DC, there's no such thing as "out of phase" - it's either on at whatever voltage (positive or negative) the supply is supplying, or it's off (0v). Unless you mean that since the electrons are flowing in an opposite direction, they're "out of phase" from the electrons in a positive voltage.


JW