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Unread 08-17-2003, 08:06 PM   #7
airspirit
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Join Date: Jul 2002
Location: Moscow, ID
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Wait ... I'm starting to think here: -20V, that's like just reversing the leads, right? So I could use a 20V thingy, and just attach the ground side to the -20V input and attach the ground from that to the 20V lead, right? Does that make sense? Reversing flow would cause the negative voltage, right?

The reason I ask is that I found a 12V->20V converter for car to notebook power, and I'm thinking that if I cut the lighter plug and attach a molex and then cut the power plug and solder that to the pins, I should be good ... right?

Or alternately, here is a picture of exactly what I need:

http://www.optrex.com/SiteImages/Par...C/50773age.pdf

In section 4.2 it gives an example of a power supply for the contrast to provide the -18 to -20V. I can find the 2SA1202, I think, but I don't understand the rest of the diagram. The resistor symbol with "VR" next to it is unfamiliar, as is the symbology used around "Tr". If someone could explain this I would be ever in their debt.

edit: this loop uses a maximum of 4.5 mA for the contrast adjustment. 20 mA would be more than enough. I found the premade eval kit you directly linked to (already built ... very nice!), but I can't seem to order it as it is unpriced. I'm going to try to contact them on Monday if I can't find another solution.
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