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100r Ohm pots

foulmist

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rhd

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foulmist said:
Hey, rhd..

I coudn't find any trimmer/pot less than 1 ohm... but 1 ohm might do good for what ever you need it... if it is multiturn ;) (but I couldn't find those either) :D

will these work for you?
TRIMMER 1 OHM 0.5W TH 306 CTS Electrocomponents Datasheet
POT 1 OHM 9MM SQ PLAST

what resistance do you need actually?
Click to expand...

I was excited to find that particular trimmer too - except that despite the title, they don't appear to actually have a 1 ohm trimmer in the orderable parts (below the title)
 
foulmist

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rhd said:
I was excited to find that particular trimmer too - except that despite the title, they don't appear to actually have a 1 ohm trimmer in the orderable parts (below the title)
Click to expand...

yeah.... I could only find 2.2ohm POT (big one/rheostat) rotary on farnell 25W? :D it seems there isn't a market on these... :(

25W 2.2R POT
 
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rhd

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foulmist said:
yeah.... I could only find 2.2ohm POT (big one/rheostat) rotary on farnell 25W? :D it seems there isn't a market on these... :(

25W 2.2R POT
Click to expand...

Is there any way to effectively achieve the same thing (a 0.1 to 1 ohm range) with another small component?

I think paralleling the pot with a fixed resistor would produce too much of an exponential resistance, even if the pot was exponential itself.
 
Cyparagon

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Digikey has some, but they want $40
wow.gif


Might I suggest Ni-chrome wire with an alligator clip as the wiper? What is the for, anyway?
 
rhd

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Cyparagon said:
Digikey has some, but they want $40
wow.gif


Might I suggest Ni-chrome wire with an alligator clip as the wiper? What is the for, anyway?
Click to expand...

It's for a small driver design.

What are drivers using then, when most of these IC's have voltage references that imply sub 1 ohm (in some cases ~ 0.1 or 0.05 ohn) resistors for current setting?

Do ultra low resistance SMD trimpots not exist, or do they just not exist at digikey/mouser, etc ?
 
Cyparagon

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It is easier to change the reference voltage than it is to directly vary the sense resistor. Stolen from Benm's site, something like this:

opamp_source_1.png
 
rhd

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Cyparagon said:
It is easier to change the reference voltage than it is to directly vary the sense resistor. Stolen from Benm's site, something like this:

opamp_source_1.png
Click to expand...




That's an entire driver though. I'm not looking for a new driver design.
 
foulmist

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placing a resistor in parallel with the pot is not a good idea... you won't be able to fine tune it when turning and will jump from small values to big...

I can't find any 1ohm pots,.... there are only 10ohm minimum ...
Why don't you use a fixed resistor value for the sense resistor?
Or maybe some jumpers for 2 or 3 resistors in parallel/series to set the current?

probably the best idea ... :beer:
 
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