1
\$\begingroup\$

1)What are the rating for these kind of presets? I need the maximum current they can withstand without any harm, (Imax). [data need for a 100k preset]

preset

enter image description here


2)I'm hoping to use this kind of voltage divider method to set reference voltages to a voltage comparator circuit. Because ref voltage should be able to adjust. Is there any good method to set reference voltages rather than this?

\$\endgroup\$
4
  • 1
    \$\begingroup\$ The weak link is not what current enters the top or bottom of the resistor but what enters or leaves the wiper. \$\endgroup\$
    – Andy aka
    Oct 2, 2013 at 9:38
  • \$\begingroup\$ How much voltage are you using that you would put enough power into a 100k trimmer to damage it? \$\endgroup\$ Oct 2, 2013 at 9:47
  • \$\begingroup\$ I haven't decided the Vmax yet. To decide that I need the maximum current (Imax) that the preset can withstand. Assume that output draws no current. \$\endgroup\$
    – Niyu
    Oct 2, 2013 at 9:53
  • 2
    \$\begingroup\$ I'd consider using a multi-turn pot for setting a control voltage on a comparator - more reliable and easier to set the precise value because they are multi-turn. \$\endgroup\$
    – Andy aka
    Oct 2, 2013 at 10:01

2 Answers 2

1
\$\begingroup\$

Here's one you could use: -

enter image description here

The important parameters are shown in red

  • Wiper current = 50 mA
  • Power rating = 0.2 W
  • Max voltage across pot = 100 Vdc

If you use the maximum power limit (0.2 W) and the resistance (100 k\$\Omega\$) you can calculate the maximum allowable voltage across the device: -

\$Power = \dfrac{Voltage^2}{Resistance}\$ therefore voltage = \$\sqrt{0.2\times 100k}\$ = 141V.

However, it says in the spec the voltage limit is 100 Vdc so, what current would flow into the 100 k\$\Omega\$ pot if this voltage were applied? Answer is 1 mA.

This tells you that you need to ensure you don't put more than 100 V across it and you won't get more than 1 mA and your power rating won't be exceeded.

Because the value of the pot is so high, it will never pass enough current to cause a problem with the wiper. This statement is made with the understanding that the wiper takes no current as per a comment made by the OP.

However, it's very important that if you have a circuit where the wiper does draw current, you keep it well within the boundaries stated in the data sheet.

\$\endgroup\$
1
  • \$\begingroup\$ @DaveTweed I shall add what the OP says in one of his comments about not using the wiper into a load. \$\endgroup\$
    – Andy aka
    Oct 2, 2013 at 12:14
0
\$\begingroup\$

I used pots like this one up to 7-9mA any higher than that tends to be damaging them.

\$\endgroup\$
1
  • \$\begingroup\$ I dont need to pass a much current It would be 5mA<. So Imax will not become a big issue I guess. Thank you. \$\endgroup\$
    – Niyu
    Oct 2, 2013 at 10:39

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.