J
John
- Jan 1, 1970
- 0
Instead of manually adjusting a pot (voltage divider) to set the
desired current level through a servo loop (op-amp driving a FET), I'd
like to use a PIC controlling a DAC. My problem is that even
rail-to-rail DACs only go down to a few millivolts, not true zero
volts, when the DAC code is zero. This few millivolts prevents me
from setting my current levels low enough for my use. I have a bunch
of servo loops and it adds up quickly.
I was thinking that I could have the PIC multiply the desired DAC
output code by X and then set up a resistor voltage-divider on the
output of the DAC to divide the voltage by that same X amount (before
going on to the servo loop's op-amp). This would reduce the zero-code
output voltage level by X times and give me a much lower minimum
current level for each servo loop. Using my existing setup, I can set
X = 30 or so, maximum.
Is this a reasonable way to reduce the effect of the DAC output not
being able to reach a true zero volts? Is there a better way? Level
shifting of some kind?
Thanks!
-- remove SPAMMENOT for e-mail responses --
desired current level through a servo loop (op-amp driving a FET), I'd
like to use a PIC controlling a DAC. My problem is that even
rail-to-rail DACs only go down to a few millivolts, not true zero
volts, when the DAC code is zero. This few millivolts prevents me
from setting my current levels low enough for my use. I have a bunch
of servo loops and it adds up quickly.
I was thinking that I could have the PIC multiply the desired DAC
output code by X and then set up a resistor voltage-divider on the
output of the DAC to divide the voltage by that same X amount (before
going on to the servo loop's op-amp). This would reduce the zero-code
output voltage level by X times and give me a much lower minimum
current level for each servo loop. Using my existing setup, I can set
X = 30 or so, maximum.
Is this a reasonable way to reduce the effect of the DAC output not
being able to reach a true zero volts? Is there a better way? Level
shifting of some kind?
Thanks!
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