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Beginners Question regarding - Voltage in a rail splitter.
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MatthewMachinist



Joined: May 19, 2020
Posts: 6
Location: New Zealand

PostPosted: Thu Jul 30, 2020 2:12 am    Post subject: Beginners Question regarding - Voltage in a rail splitter. Reply with quote  Mark this post and the followings unread

I am a bit confused as to what is going on with the current in a rail splitter circuit. Actually I downright confused about negative voltage in DC circuits.

Let’s say I had 24v DC and used a rail splitter to create + and -12v. For arguments sake I will just use this schematic as an example… https://cdn.instructables.com/F4X/PE5W/H3Z3UFPV/F4XPE5WH3Z3UFPV.LARGE.gif

On the negative side of the circuit I am not sure which way the current is flowing.

I guess as a beginner I have the idea in my head that + pushes and - pulls. But I have no idea if that applies in this instance. This follows logically from the basic conception of a circuit being a circuit.

I found an article online that says…
“One example where negative voltage is used for dual supply operational amplifiers. Many times, these amplifiers deal with AC signals. Therefore, positive and negative rails need to be established; and they are established through the application of positive and negative DC voltages to the op amp.”

So that must mean that the current flows to the opamp from the rail splitter. But then it doesn’t make sense for it to be called negative voltage?

My apologies for being a confused beginner.
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Blue Hell
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Joined: Apr 03, 2004
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Location: The Netherlands, Enschede
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PostPosted: Thu Jul 30, 2020 3:46 am    Post subject: Reply with quote  Mark this post and the followings unread

Voltage is always relative to another voltage, so in a way, it is just a label you stick to one of the terminals and then the others follow.

There is a convention to declare the mid terminalto be 0 V, your reference point. It makes calculations on the circuit easier.

In the circuit example you posted for the splitter, you could relabel the output voltages .. -12V to be named 0V, 0 -> +12 V and +12 V then would be +24V.

Nothing physically changes by this of course, but maybe it makes it easier for you to understand the current flows?

Current will always flow from the higher to the lower voltage, except in a voltage generator, like your battery .. where it will flow from the lower to the higher ... miracles happen there .. (:-)

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Jan
also .. could someone please turn down the thermostat a bit.
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gabbagabi



Joined: Nov 29, 2008
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PostPosted: Thu Jul 30, 2020 6:56 am    Post subject: Reply with quote  Mark this post and the followings unread

well current is made of electrons, electrons are negative charged
so they will always flow up to the positive, means from GND to +Vsupply Shocked Shocked Shocked
since that is a bit strange for our brains to deal with the people found out that it is ok just to ignore that fact and threat it the other way round, and it works quite nice Cool Cool Cool
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MatthewMachinist



Joined: May 19, 2020
Posts: 6
Location: New Zealand

PostPosted: Fri Jul 31, 2020 10:36 pm    Post subject: Reply with quote  Mark this post and the followings unread

Thanks for the answers, your explanation Blue Hell was particularly useful.

I have been looking over a schematic for a Guitar Pedal that uses this type of power supply and its now starting to make sense... some of the op amps have the + pin connected to the ground which does make sense now.

This also means that the article which mentioned negative voltage being applied to the op amp was rather unclear
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Blue Hell
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PostPosted: Sat Aug 01, 2020 5:21 am    Post subject: Reply with quote  Mark this post and the followings unread

Cool

And re. what gabbagabi wrote .. there is a historic reason for this oddity.

At the time it was discovered that there could be such a thing as a current of electricity it was not known what the carriers of such a current could be.

Electrons were to be discovered at a later time and then as a big surprise they happened to be labeled by a charge that people happened to identify as negative.

By then it was too late to change things, and it did not matter too much anyway, unless you would study the details of devices like vacuum tubes.

In more recent times a lack of electrons was discovered to more or less behave as particles too, they were called holes, places where an electron could be but wasn't; and so you could have holes travel as the carriers for electricity from + to -, a view used in describing the workings of semiconductor devices.

Anyways, nowadays we make them electrons dance with the holes and we call that electro-music Laughing

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Jan
also .. could someone please turn down the thermostat a bit.
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