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16 years ago
Creating a voltage-controlled resistance
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16 years ago
Alternate?, Not really, the signal is just an ON/OFF, not a +/- signal. for example. setting a carry of 50khz for the PWM and adjusting the duty cycle and passing it through a Resistor will be very smooth as long as the batteries are connected. You'll want to pick a resistor that will not allow the driving device to exceed it's max I (current) if fully shorted. this same resistor can also be used as the current monitor shunt :) a nice like differential input would work nicely for this to give you a linear current range.
P.S. when deriving the signal around this resistor for the current sense, you'll want some by pass caps at the op-amp input to smooth off the PWM signal so that you can get a rather steady reading. WIth a carrier of 50Khz, they should be rather small.
-- "I\'m never wrong, once i thought i was, but was mistaken" Real Programmers Do things like this. http://webpages.charter.net/jamie_5
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16 years ago
I should have said fluctuate. One of the factors I'm interested in studying is current draw so using PWM, a constant current, and a constant resistance will give me a few things to compare. I'm planning on using a few of the circuits suggested so I can become more familiar with the components and the differences in the designs.
Thanks for the suggestions all!
Dave
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16 years ago
Maybe something like this for an adjustable constant resistance.
PNP Darlington --------------- ------------ | | v / | --- | --- | Battery - | | | | | | | === | .-. | GND | | | | | | | | | '-' | | | | | | | 0.1 Ohm to 100 Ohm |--------/^\\-------- | Adjustable constant | /- +\\ | | Resistance | '-----' | | | | | | | | | | === | | | | GND | 100k .-. | | | | |