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-   -   Electronics question - variable resistors/pots (http://www.fordtruckfanatics.com/forum/showthread.php?t=40110)

CowboyBilly9Mile 06-26-2016 03:54 PM

Electronics question - variable resistors/pots
 
Same general question, two different scenarios.

a) trim pot used to adjust voltage to the base of a transistor......the center/variable end goes to the base, one end on the carbon band (for lack of better desc) goes to the supply voltage and the other goes to ground.

Q. Why the ground connection? Stability? To establish a possibly used maximum resistance between the supply voltage which may keep some component of the supply, such as an IC, active?

b) trim pot in series used to adjust voltage, the center/variable is tied to one end of the carbon band and together these form one connection; the other connection is the other end of the carbon band.

Q. Why is one end of the carbon band tied to the center/variable connection and together they form one connection? Again, stability?

DNFXDLI 06-26-2016 07:51 PM

If the pot ends are tied to the supply and ground, it forms a voltage divider...if you are only using 2 pins you wind up controlling current...like a rheostat.

On the connection to ground, you are using that as the reference..and there will always be a current flow from the two fixed ends of the pot.

CowboyBilly9Mile 06-26-2016 08:21 PM

Quote:

Originally Posted by DNFXDLI (Post 680012)
If the pot ends are tied to the supply and ground, it forms a voltage divider.

Makes perfect sense.

Quote:

Originally Posted by DNFXDLI (Post 680012)
if you are only using 2 pins you wind up controlling current...like a rheostat.

Is this the ans to Q #2?

Quote:

Originally Posted by DNFXDLI (Post 680012)
On the connection to ground, you are using that as the reference..and there will always be a current flow from the two fixed ends of the pot.

That's along the lines of what I was thinking.

DNFXDLI 06-26-2016 08:29 PM

Yes regarding question 2.

Also, I'm assuming you are using linear devices...Logs or reverse Logs or whatever the hell else they are making now would be entertaining to say the least :D

CowboyBilly9Mile 06-26-2016 08:40 PM

Quote:

Originally Posted by DNFXDLI (Post 680015)
Yes regarding question 2.

Also, I'm assuming you are using linear devices...Logs or reverse Logs or whatever the hell else they are making now would be entertaining to say the least :D


Ok, so on the 3-pin pot, two pins become one as descriobed, and the device now functions with those two now counting as one, and then the one other pin, and regulates current. Right?

DNFXDLI 06-26-2016 08:58 PM

Yes.

CowboyBilly9Mile 06-26-2016 09:03 PM

Excellent, thank you for answering the Q's it's always most appreciated! :)

DNFXDLI 06-26-2016 09:04 PM

Anytime Bill...just remember that I have not farted around with this stuff for 30+ years.

CowboyBilly9Mile 07-24-2016 07:47 PM

Well darn, smoked my only 10K pot. :headbang:

Edit: Stunk worse than the fried IC to boot.

DNFXDLI 07-24-2016 08:12 PM

So it did limit the current once it released the magic smoke :p


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