View Full Version : Problem with 595 output voltage

11-20-2011, 09:06 AM
I wanted to drive the new FAST drip lights with my 595. In testing it seemed to work, but as usual in practice not so good. The output from the driver is 4.45v. The power supply is 5.10. The issue appears to be that the 2803 never goes completely low. It always has about .55 volts on it. I tried a pull down resistor of several sizes but none made a difference. I tried using a 10v power supply on the alternate input for the 2803. I still got 4.45v output. I looking for ideas without having to build DCSSRs to solve this issue.

12-31-2011, 12:10 AM
Hi, cobraman44.

Just stumbled on your question. It's probably cold by now. If you are referring to VCE(sat) of the ULN2803 as being .55V then that is normal for this chip. The datasheet has it as high as 1.1V @ 300ma for a typical low. Darlington drivers tend to be higher than non-darlington drivers. Perhaps I misunderstood what you are trying to do since I didn't see your circuit.