Where direct current?

In one article on Habre explains how to get 7V from the power supply. Sorry for the stupid question, but I can not understand how it is a steady current when connected to +12V and +5V. And where a minus? Can just give a link to me to read.
April 19th 20 at 12:38
1 answer
April 19th 20 at 12:40
Solution
a potential difference of 12-5=7
connect what/where?
example:
if you connect + output of the fan to +12V,
and - output to +5V,
the fan will 7вольт.
That is, it is always considered to be just less than the voltage that usually is equal to zero?
And slightly still do not understand, is it harmful for the circuit? Well, that is some kind of engineer designed this unit power contact +5V some the consumer will get current with a voltage of 5V, and the author of the article, it turns out that there current "merged". - emmalee_Stoltenberg commented on April 19th 20 at 12:43
@emmalee_Stoltenberg,
like that ))),
you're just a little confused minus and common.
there are schemes with bipolar ±,
i.e. relative to the common wire/zero, there is a voltage +5V and -5V - Odell.Kuhic30 commented on April 19th 20 at 12:46
@emmalee_Stoltenberg, it depends on whether there is a load between 5V and ground. If it is more current than the intake fan, then nothing will happen. If less, then a computer PSU just shuts down (most likely) due to excessive line voltage of 5 V. - Lempi_Yundt92 commented on April 19th 20 at 12:49

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