wide-range Voltage Controlled Resistor--for use as variable load
wide-range Voltage Controlled Resistor--for use as variable load
(OP)
I'm trying to find something that would work as a voltage-controllable resistive load. I thought something simple might be available--where a DC control voltage could be used to yield a range of resistance values. Here are the basics:
- Resistance: span ~ 200-20,000 ohms.
- Sink capability: DC source voltage/current up to 7 Volts/50 mA.
- Control voltage: negotiable.





RE: wide-range Voltage Controlled Resistor--for use as variable load
http://www.p3america.com/motorized_potentiometers_...
http://www.google.com/url?sa=t&rct=j&q=&am...
MikeL
RE: wide-range Voltage Controlled Resistor--for use as variable load
You do realize that the word transistor is the compounding of "transfer resistor?" You can use a couple of transistors in a current mirror configuration, and control the mirrored current.
TTFN

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RE: wide-range Voltage Controlled Resistor--for use as variable load
Dan - Owner
http://www.Hi-TecDesigns.com
RE: wide-range Voltage Controlled Resistor--for use as variable load
I’ll research the suggestons further. Thanks for the thoughts.
RE: wide-range Voltage Controlled Resistor--for use as variable load
http://www.ti.com/lit/ds/symlink/lm13700.pdf
Alone, it won't get you the current range you want, but the basic circuit topology could be made beefier with some additional circuitry.
A few questions: what frequency range do you need for the resistor? DC to a few kHz is one thing, MHz is another. How fast do you need to be able to modulate the resistance? Do you need this resistor to be floating, or can one side be grounded? If ground referenced, the job is much easier; an op amp and a multiplier chip can do it.
RE: wide-range Voltage Controlled Resistor--for use as variable load
- The frequency is essentially DC.
- I’m looking to switch the load in milliseconds at worst.
- One-side grounded would work.
I've done a lot of reading/searching. A motor-operated pot does what I'm looking for in principle, but I don't know that it quite fits. I looked at the OTA’s, et al. I have the TI datasheet on the LM13700, and saw that VCR application referenced. I tried messing with a feedback/voltage-controlled constant current source that I put together, and looked at some buck-boost circuits. I think these things are close, but it seems tough to get the full range. I’m trying to match resistances at current levels down to ~1 mA or less… that’s what drives the higher resistance values noted above.As a placeholder, I have precision resistors simply selected via analog switches, giving a brute force range of 150 ohms up to 6k ohms. The main issue is the lack of continuous coverage
Thanks for your thoughts….