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# What does TTL really do?

#### sometoymachine

##### New member
qumefox: I measured the voltage from the 5v and 12v and the 5 was a steady 5.22v and the 12v was steady at 12.02. Guess its ok then.

Thanks anselm for the link, that helped me out a lot actually for a totally different reason. Helped clarify the - and + voltage. It seems that the guy in the tutorial used different voltage lines to form a complete circuit. Ie. He said that the Yellow (+12) and the Red (+5) created 7v. also used the (-12) and (+5) to create 17v. This sound legitimate to you? It actually sounds to mesh with the original video that I saw which made me lean towards the power supply for my first laser (mainly larger parts and all homemade) In this video, the guy goes into zero detail about why, but he says to use the yellow (12v) for positive and the red (5v) for negative:

It seems to me that if i could produce 7v, it would be more ideal for my use with a lpc-815 and the DDL as opposed to 12v, which would only generate more heat at the regulator correct?

#### anselm

##### New member
This sound legitimate to you?
Sure. It's simple arithmetic, addition and subtraction.
Like when you put two AAs in series to get 1.5+1.5=3V.

Just remember, the negative voltage supplies cannot supply more than 0.5A usually.
It should say so on the sticker on the PSU.

Using +5 and +12 to get to 7V should do fine though, they are both
rated for enough amperage.

#### HIMNL9

##### New member
^ careful, with these combinations ..... not all the PC PSUs have the same circuitry, as voltage regulation ..... if one of your cross-connections "fool out" the regulator, you can end with more voltage, or less, or an oscillation at output .....

I suggest you to do these tests with resistors and oscilloscope as load, before to connect some expensive LD in that way .

#### sometoymachine

##### New member
Awesome.

Oh i'll definately put it on a test load first. I already learned the hard way.

#### sometoymachine

##### New member
Oh, and the output for the two lines are: +5v /32A and +12v /16A.

#### Toaster

##### New member
Do have a US version of that anywhere?

#### qumefox

##### New member
do you mean made in the US, or just ships from the US? I think some retail outlets like frys carries something similar.

#### Toaster

##### New member
Sorry. I feel like a dumb ass, I cant remember if US wall sockets are 220V or 110V. That PSU is for 220 And I was thinking we were 110V