# High Frequency Variable Resistor

#### Firenze02

Joined Sep 1, 2018
44
Hi,

I'm looking for a variable resistor (rheostat) able to operate also with high frequency current. In particular, for my application, the current is sinusoidal with f=100kHz and amplitude of 40A.

The range of variable resistance should be 0-200 Ohm and 0-10 kOhm (obviously for higher value of resistance the current won't be 40A ).

Can you suggest some device that I could buy?

Thank you.

#### Alec_t

Joined Sep 17, 2013
11,972
The range of variable resistance should be 0-200 Ohm and 0-10 kOhm
So you want two rheostats?
obviously for higher value of resistance the current won't be 40A
It isn't obvious.
What will be the current at the 200 Ohm setting?
What will be the current at the 10k Ohm setting?
What is your budget? (High current rheostats are likely to be expensive).
What is your application that requires 40A at 100kHz? There might be a better way than using rheostats to provide current control.

#### andrewmm

Joined Feb 25, 2011
1,127
Hi,

I'm looking for a variable resistor (rheostat) able to operate also with high frequency current. In particular, for my application, the current is sinusoidal with f=100kHz and amplitude of 40A.

The range of variable resistance should be 0-200 Ohm and 0-10 kOhm (obviously for higher value of resistance the current won't be 40A ).

Can you suggest some device that I could buy?

Thank you.
looks like your actualy after a FET ,
but remember the power law power = I * I * R , at 40 amps thats a lot of heat even into 1 ohm,..

#### DickCappels

Joined Aug 21, 2008
7,147
Can you tolerate a little distortion of the waveform, and will the frequency be constant? Can you specify the granularity you need (for example, 1% steps)?

#### ronsimpson

Joined Oct 7, 2019
1,156
f=100kHz and amplitude of 40A.
0-200 Ohm and 0-10 kOhm
I have used adjustable power resistors. Not easy to adjust and does not have a knob. Up to 1000 watts.

This next one you can not afford. It adds a easy way to adjust.

Here is what I am looking for. I found these at digikey.com under "Rotary Potentiometers, Rheostats" Go to the link and look under "power" and then select 100 watts to 1000 watts to remove the little parts.

All of these are not good at high frequencies. I think 100khz is a little too high but worth a try.

#### KeepItSimpleStupid

Joined Mar 4, 2014
4,549
You would have to look at the inductance of the rehostat. The corner frequency will be fc= 1/(2*PI*R*C). Fc is defined as when the out put is -3db down or 70.7% or sqrt(2) down from 0db.

You should also be able to use an electronic load.

https://mfjenterprises.com/collections/dummy-load Although not variable, they do offer a high frequency dummy load of 50 ohms. I used one of the bucket varieties for a 1000 W 13.56 MHz system.