piclist 2002\11\03\152731a >
Thread: Controlling resistance
face BY : Russell McMahon email (remove spam text)

> Thank you for all your suggestions. But in regards to the current capacity
> the dpot, I do'nt think that will be a problem. Reading the lm317
> it appears that only a few uamps pass through the adjustment pin, which

> > I am not sure if the ADG736 can handle the [adj] current
> LM317 adj current is only 50-60uA for 10mA < Iout < Imax
> www.analog.com/productSelection/pdf/ADG736_0.pdf
> shows through-current for ADG736 is 30mA max (4066 is 25mA)

> Wherever you get that. LM317 adj current is exactly 120uA no matter what
> the load.

All above are in the order of right but all are wrong in the context (my
turn will come (or may have already :-) )).

While the ADJUST PIN current is in the order of 50 to 100 uA this is not
solely what the control element must handle. It must also handle the current
through the upper resistor of the voltage setting divider which is typically
designed to be 5 mA. Still well within spec for the control device
mentioned. Also note that the voltage at the adjust pin will be 1.2v less
than full output voltage.


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