View Full Version : Power for Single 595

12-22-2007, 07:48 PM
I've got my 595 up and running. I have the coop 595 and SSR boards both fully populated. I'm using an IBM X31 laptop (It actually has a parallel port). And for now I'm using a USB port to supply the 5 volts to the 595. So far I'm ok, but I've only got 31 channels working. I hope to get the remaining 24 planned for this year installed in the next day or so, but I'm not sure if I'll end up pulling more than the USB can supply.

I was going to use the 5V part of a 5V / 12V brick that I have from an external HD. After prying open the case I've gotten to the pins I want to tap and the meter indicates 5.18 Volts. USB usually puts out 5.0x volts. X is typically < 4 with my meter.

So, the question is, if I plug in this supply, will it be too much voltage for the 595 and / or SSRs? I know USB is theoretically only good for 500 ma, and my HD supply indicates 1.5A. There are two USB ports on the laptop, so I'm not sure if it would really let me pull 1A out of one if there is nothing on the other or not...


It's kinda funny, cause I can see the pair of voltage regulators on the heatsinks in the case, so I'm not sure why the voltage would be off....

12-22-2007, 09:20 PM
Not a problem.
I run everything off of hard drive power connectors.

240 channels of renard @5v
8 DMX pixels @12v
1 belkin transmitter @ 12v


P. Short
12-22-2007, 09:40 PM
The 5.18V should be fine, the HC chips used there are good for at least 5V + 5%, usually more.

And I don't think that the USB port is required to source more than 100 mA if you don't have a recognized high-power peripheral plugged in. You may be able to get 500 mA by just connecting wires to the power pins on the USB port, but there is no guarantee.



Edit: As to why the voltage is 5.18V, there is always a tolerance spec on the regulators, they will rarely be exact. It is not uncommon for the voltage tolerance to be +/- 5%, which is .25V.



12-23-2007, 11:52 AM
As others have said the 5.18V should be fine. In addition, as you put a load on it the voltage is likely to come down somewhat.