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Old 07-15-2011, 06:00 PM #1
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Default Why use a pot and not variable resistor?

Hi, a noob question and just want an explanation as to why the DDL driver uses the trimmer in a potentiometer configuration rather than as a variable resistor which would seem like the most obvious route.

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Old 07-15-2011, 06:22 PM #2
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Default Re: Why use a pot and not variable resistor?

Trimmer (resistive), Pot (potentiometer), and Variable Resistor, are all the same thing, an adjustable resistance. You can wire it as a divider (1 leg of resistive element to one part of circuit, wiper to another part, and other resistive leg to yet another part), or you can wire it as a limiter (one leg of resistive element to one part of the circuit, the other leg of the resistive element and the wiper both tied to another part of the circuit). In the limiter configuration, it really does not matter (electrically) if the second leg and the wiper are both tied to the other part of the circuit together, as long as the wiper is tied to that other part of the circuit. It is an old legacy practice from old radio days, to tie the wiper and other leg together, in this configuration, to insure that, in the case of a seperation of the wiper from the resistive element, that you still have a complete circuit (with some resistance in it).
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Old 07-15-2011, 06:52 PM #3
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Default Re: Why use a pot and not variable resistor?

Oh right, so its just a safety precaution so if your wiper gets burnt out then the circuit is still connected but now the pot will be the maximum value of the pot (depending on the terminals you have shorted).

Thanks for the speedy reply
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Old 07-15-2011, 07:00 PM #4
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Default Re: Why use a pot and not variable resistor?

Kinda sorta,,,
Usually you don't burn out a wiper, you burn a whole in the resistive element (not al the way across it, just where the wiper makes contact), or, you get a build up of crud that eventually seperates the wiper from the resistive element. But, yes, the principle is the same.
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