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I ordered this power supply unit to provide 3.3V filtered power to a video transmitter.

I attached the input and output power leads, soldered the proper voltage selection pads, and it works as advertised.

But I'm curious as to what the "signal" circuit does. Can anybody load me a clue?

enter image description here

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I bet the other side of the PCB is a lot more interesting. Here there's nothing to see. – stevenvh Apr 16 '12 at 6:06
I'm pretty much guessing here, but I think you apply your signal to one pin and then read another to check if the PSU is connected. You should try and trace where that via goes to. – Armandas Apr 16 '12 at 6:27
@Armandus: not entirely impossible, but it would be stupid. The easiest would be to output Vcc to another pin, so that detection of the board simply translates to looking for Vcc on the output. No "signal" required. – Federico Russo Apr 16 '12 at 8:33
You really should be asking the manufacturer. Unfortunately from other things on the web site you linked to they seem to be rather clueless. Some power supplies have sense lines. These can be used to provide voltage feedback at the point of load with separate wires with little current thru them providing the signal. This allows the supply to compensate for voltage drops in the cable and connectors. I've never heard sense lines called "signal" though, so I can't tell whether that's what they are. – Olin Lathrop Apr 16 '12 at 12:50
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I am guessing that it is an "Enable" signal or such, which will accept a logic level signal to turn the switcher ON and OFF. What happens when you solder that jumper and give nothing to the "Signal IN" and "Signal OUT"? I wonder why they broke the ground plane to route that signal, though, it can be routed through the edge of the PCB or it could sneak around as it is not that critical in the case of signal integrity. – abdullah kahraman Apr 16 '12 at 13:48
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1 Answer

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I found your board http://www.hobbyic.com/products.php?product=Step-down-PSU-3.3v-5v-9v-12v. The regulator chip info is obfuscated and their documentation online is nil. Usually these chips have a RUN input . But with 8 pins and 4 step down voltages, it wont handle too much power. (Note dont use on 1W video cam.)

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It shouldn't have been hard to find since he included the link in the question. – The Photon Apr 17 '12 at 23:43
So, where's the answer to his question? – stevenvh Apr 18 '12 at 17:32
you mean my answer "RUN input"= signal was hiding? The best answer lies in the supplier's documentation. Contact them. – Tony Stewart Apr 19 '12 at 0:41

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