[time-nuts] OXCO Issues -- Latest
jimlux at earthlink.net
Sun May 12 16:24:12 EDT 2013
On 5/12/13 12:38 PM, Al Wolfe wrote:
> Years ago we were taught that it was poor engineering practice to use
> pots to trim a DC value, especially if any appreciable current was to be
> drawn from the wiper. (Probably true for any kind of signal on a pot) It
> seems that current through the wiper would eventually erode away the
> material under the wiper. This is true especially for set-and-forget
> applications. If the wiper is used only as a voltage reference and very
> little current drawn then it is probably OK for most situations.
> Probably the best design is to use fixed resistors for most of the
> voltage divider circuit and the variable element be a small fraction of
> the total divider resistance.
This is what those EEPROM based electronic trimpots are great for.
(assuming you fit within the other limitations of use). Basically,
they're an array of FETs on a resistor network, and even with the power
off, they have the same value.
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