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I have a 48 VDC transformer for a cicso phone that is simply a two wire (+ and -) but i was wondering if i could just slap on some super resistors (in the megaΩ category). Could I?
The amount of voltage a resistor drops is directly linked to the current through it.
So unless you have a load that will always consume about the same amount of current, it won't guarantee the same output voltage.
You could use a linear regulator to put out 12v and you wouldn't have to worry about the load.
The problem with both above methods is that you have to DISSIPATE that 36 volts in the form of heat. So at say, 1 amp of current draw, you're dissipating 36 watts of heat.
Another option(and likely your only) is using a DC-DC converter to clamp the voltage down.
Much better to find a DC wall-wart that puts out about 3V more than 12V, and then use an IC regulator chip to make a "regulated" 12V. Or if you can find a "regulated 12Vdc" wall-wart, that would work, too.
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