Monday, October 21, 2013

An Incorrect Guess About The Voltage Regulator

In a previous post of mine about the Zalman fan controller, I guessed that the voltage regulator was an LM317T. I came across a blog post about the same controller and the author said that the voltage regulator was a 7805. So I decided I had to verify that I was wrong. And I was. I desoldered the regulator from the board so I could identify it.
Fairchild KA7805. I’m not sure what E33 means. “Although designed
primarily as fixed-voltage regulators, these devices can be used with external components for adjustable voltages and currents.”
The resistor measures 708 ohms. I was wrong about it and the potentiometer as well. In-circuit measurment is not always ideal. Likewise reading resistor color codes in bad light through a small aperture is difficult.
Violet, brown, black, black, brown, a 710 ohm, 1% resistor.
The potentiometer measures between just over 0 ohms and 1K ohms.
Hey, I have some 7805 regulators in my parts library as well, so I can still make some fan controls if I want. Not that I will. And yes, I soldered it back together.

1 comment:

Unknown said...

Thanks, exactly what I was looking for - I intend to mod one of those so that the vIn is taken not from the mobo connector, but directly from a PSU. I intend to use it to voltage-control 3 fans via a fan hub. Zalman itself lists the max power draw at 6W, please correct me if I am wrong, but it means that if the total current of all three amps is within 500mA, I should be good? And if a little more - how much "a little" is still safe? 600mA? 700?

Thanks in advance.