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Old 11-07-2011, 12:56 PM #17
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Default Re: 100r Ohm pots

Quote:
Originally Posted by rhd View Post
What about sub-1-Ohm trimmers/pots/trimpots ?

Even low wattage ones. Does this exist?
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)

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?



Last edited by foulmist; 11-07-2011 at 01:00 PM.
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Old 11-07-2011, 01:05 PM #18
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Default Re: 100r Ohm pots

Quote:
Originally Posted by foulmist View Post
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)

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?
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)
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Old 11-07-2011, 01:44 PM #19
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Default Re: 100r Ohm pots

Quote:
Originally Posted by rhd View Post
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)
yeah.... I could only find 2.2ohm POT (big one/rheostat) rotary on farnell 25W? it seems there isn't a market on these...

25W 2.2R POT

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Old 11-07-2011, 02:08 PM #20
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Default Re: 100r Ohm pots

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

25W 2.2R POT
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.
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Old 11-07-2011, 06:01 PM #21
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Default Re: 100r Ohm pots

Digikey has some, but they want $40

Might I suggest Ni-chrome wire with an alligator clip as the wiper? What is the for, anyway?
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Old 11-07-2011, 06:09 PM #22
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Default Re: 100r Ohm pots

Quote:
Originally Posted by Cyparagon View Post
Digikey has some, but they want $40

Might I suggest Ni-chrome wire with an alligator clip as the wiper? What is the for, anyway?
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 ?
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Old 11-07-2011, 06:32 PM #23
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Default Re: 100r Ohm pots

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:

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Old 11-07-2011, 07:00 PM #24
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Default Re: 100r Ohm pots

Quote:
Originally Posted by Cyparagon View Post
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:




That's an entire driver though. I'm not looking for a new driver design.
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Old 11-07-2011, 08:20 PM #25
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Default Re: 100r Ohm pots

Yes, but you asked:

Quote:
Originally Posted by rhd View Post
What are drivers using
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Old 11-08-2011, 05:39 AM #26
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Default Re: 100r Ohm pots

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 ...

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