fine tuning potentiometers - parallel and series

A

avner

Senior Member
Hi

I am looking for a way to setup 3 potentiometers, so one of them is used as the "power dial"
one of them set the maximum value, and one the minimum.

the thing is, that it is not a voltage divider.
which means the ohm value is critical all the way. (not just the proportional 'travel' of the pot,)

I once saw an arrangement that would allow to tun the main diam to the minimum, then set the minimum tuning trimmer,
then set the main diam to maximum, and then set the maximum trimmer.
but setting the maximum trimmer won't change the value of the minimum level.

do you have any idea ?
 
i tried to draw that from my head from what i remember.

the minimum will work for sure.
but i'm not sure of the maximum part, something seems tricky when i calculate this,
like if the main dial has some parabolic shape

pot.jpg
 
What you will need are two relatively small resistance pots for the minimum and maximum and a larger one for the setting.

The max pot will go from V+ to ground and the wiper will connect to the "top" of the setting pot.
The min pot will go from V+ to ground and the wiper will connect to the "bottom" of the setting pot.

Adjusting the max and min pots will set the "supply" voltage across the setting pot, limiting its voltage.
 
ys that would work as a voltage divider,
ple read my original message - i wrote that the thing is current driven and not voltage

i actually have two wires and the setting is by the ohmic value.
i dont use v+ and ground for this, and maybe the chip has already some resistors inside which i dont know of.

from datasheet:
Output Voltage VI Converter Pin.
Develops a current proportional to output capacitor voltage.
Connecta resistor between this pin and the drain of the NMOS.
 
avner said:
snip
maybe the chip has already some resistors inside which i dont know of.

from datasheet:
Output Voltage VI Converter Pin.
Develops a current proportional to output capacitor voltage.
Connecta resistor between this pin and the drain of the NMOS.
Click to expand...

The obvious questions:

What chip?

What datasheet?

e
 
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