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Old 09-14-2018, 12:37 PM   #7
Dannyx
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Thumbs up Re: Modifying laptop adapter for 12v

Quote:
Originally Posted by momaka View Post
changing the lower resistor in the divider might be preferable to do, as it doesn't mess with the circuit's compensation.
By "lower resistor" you're referring to the one going to GND ? I was concerned that lowering the resistance between that pin and GND will cause more current draw, so I thought I'd lower the VCC one instead, though now that I think about it, it's silly really, since an op-amp has very little (ideally zero) current going into its pins, so it shouldn't be an issue even if shorted to GND directly (in which case, theoretically speaking, the output would drop to the minimum possible value of around 2.5v which is the reference).

CORRECTION: with the inverting input tied directly to GND, the output would shoot up to the maximum possible value...whatever that might be, because now the NON-inverting input is always going to be higher than the inverting input (which is grounded) and never allow the output of the op-amp to swing low to turn on the LED, so the primary would try pumping even harder to reach equilibrium.
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Last edited by Dannyx; 09-14-2018 at 12:41 PM..
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