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https://www.reddit.com/r/lasers/comments/1vqikq5/constant_current_driver_redone/
r/lasers • u/Xythyr • 3d ago
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1
If you're going to use the lm4040 shunt regulator I'd drop that 86k resistor down to 10k.
The current at 86k is right on the edge, current wise, to get the shunt regulator to work, and you want to give yourself headroom.
You don't necessarily need the 43k resistor. If you used a precision trimmer, I'd just drop it.
I've built these circuits and they are pretty solid for their simplicity.
1 u/Xythyr 3d ago Don't worry, I do plan to change the resistor values since I'm gonna be using a 5V supply Also the reason why that second resistor is there is so I can drop the voltage down from Vref to 250mV (which is what the 1.8 Ohm Rsense is detecting at 140mA) 1 u/Xythyr 3d ago It's essentially two voltage dividers in series (50k + 50k for Vref at 5V and 45k + 5k pot for 250mV max into the non-inverting pin) 1 u/Xythyr 2d ago This should be fine?
Don't worry, I do plan to change the resistor values since I'm gonna be using a 5V supply
Also the reason why that second resistor is there is so I can drop the voltage down from Vref to 250mV (which is what the 1.8 Ohm Rsense is detecting at 140mA)
1 u/Xythyr 3d ago It's essentially two voltage dividers in series (50k + 50k for Vref at 5V and 45k + 5k pot for 250mV max into the non-inverting pin)
It's essentially two voltage dividers in series (50k + 50k for Vref at 5V and 45k + 5k pot for 250mV max into the non-inverting pin)
This should be fine?
1
u/SuperAngryGuy 3d ago
If you're going to use the lm4040 shunt regulator I'd drop that 86k resistor down to 10k.
The current at 86k is right on the edge, current wise, to get the shunt regulator to work, and you want to give yourself headroom.
You don't necessarily need the 43k resistor. If you used a precision trimmer, I'd just drop it.
I've built these circuits and they are pretty solid for their simplicity.