WTD 12v linear PSU

[lilolee]

Was it marketed at 13.8 volts or whatever? Was the potentiometer external on yours?

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Yes marketed as 13.8v. Internal pot allows change of voltage. IIRC 10v to 18v

[Lawrence001]

Yes marketed as 13.8v. Internal pot allows change of voltage. IIRC 10v to 18v

Great, hopefully this is the same. I've ordered a couple from stores (last ones) will see if they actually have them

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[Lawrence001]

Forgot to ask, where do I get the cable from to connect it to the dac??

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[lilolee]

I just went through my old chargers draw and found one that fitted. Maplin sell them as well though. Make sure you get the polarity the right way around.

[Lawrence001]

I just went through my old chargers draw and found one that fitted. Maplin sell them as well though. Make sure you get the polarity the right way around.

Yes indeed! You mean you cut them off redundant chargers? Not a fan of those nasty thin cables, what's the chance of RFI etc affecting a low voltage? May be a gap in the market for these!

[Lawrence001]

Yes marketed as 13.8v. Internal pot allows change of voltage. IIRC 10v to 18v

Got my first one today. I can see 2 pots (if that's what you call these flimsy things). Is yours like this? Do you know which one does what? I've got to say it's quite weighty and chunky.

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[lilolee]

Mine only has 1 variable resistor. I find it hard to work out but just from the number I suspect vr1 sets the input voltage before the regulating circuit and vr2 the final output voltage. BUT THIS IS GUESS WORK. I would connect a MM to the out put and vary vr2 until you get the 12v you require. BUT AGAIN THIS IS GUESS WORK.

[Lawrence001]

Thanks for that, would decreasing the input voltage also make the output voltage fall (which sounds like the wrong way to achieve it) or is the point of the regulator to stop that happening? In which case, why would the input voltage be variable?

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[lilolee]

Again this is supposition, but it can be like this to allow for voltage drop across the regulation circuit ie the voltage in needs to be higher, but within a certain tolerance, than the voltage out. Remember mains varies hence the ability to vary both input and output voltage. Try googling the transistors that are in circuit, this may lead you to a circuit diagram of their usage.

I hope somebody with better circuit knowledge will confirm/correct me if I am wrong.

[Lawrence001]

Thanks Lee I'll just experiment with small changes first to v2 then v1 and see the effect on output voltage. If my device is rated 12v, I'll probably aim for about 12.2v measured.