I made a constant current source with a TL431 (or TL1431) for checking multimeters etc. It’s reasonably accurate in the 10ma range (usually within 0.05%, assuming my multimeter is absolutely accurate).
The 1ma range is less accurate, usually showing ~ 0.9944 μA (0.6%). I think this is due to the LM358’s offset voltage (or bias current?). It’s not the resistors, I spent a while manually checking and matching resistors to get more or less exactly 250 and 2500 ohms.
I know this whole circuit is very temperature sensitive and will drift a lot, but i only really care about relative accuracy between my meters, not absolute accuracy.
I’m ordering some precision low-offset voltage opamps soon, which is why i made the lm358 socketed.
I built up the circuit in Falstad’s simulator below, schematic is also in the album. https://tinyurl.com/ygpt3b26
Two interesting applications: I used it to make a constant current source for measuring thermistor temperature sensors (Pt100). Another was to make temperature compensated gate bias for RF power transistors.
Ah, I see you used the classic 330R on the LED… Today’s LEDs are far brighter and more efficient — you could drop the current with a 1K or 2K2 and it’d still likely be plenty bright!
I made a constant current source with a TL431 (or TL1431) for checking multimeters etc. It’s reasonably accurate in the 10ma range (usually within 0.05%, assuming my multimeter is absolutely accurate).
The 1ma range is less accurate, usually showing ~ 0.9944 μA (0.6%). I think this is due to the LM358’s offset voltage (or bias current?). It’s not the resistors, I spent a while manually checking and matching resistors to get more or less exactly 250 and 2500 ohms.
I know this whole circuit is very temperature sensitive and will drift a lot, but i only really care about relative accuracy between my meters, not absolute accuracy.
I’m ordering some precision low-offset voltage opamps soon, which is why i made the lm358 socketed.
I built up the circuit in Falstad’s simulator below, schematic is also in the album.
https://tinyurl.com/ygpt3b26
Very nice!
Well done, now ovenize that to keep the temperature stable.
I love the TL431.
Two interesting applications: I used it to make a constant current source for measuring thermistor temperature sensors (Pt100). Another was to make temperature compensated gate bias for RF power transistors.
Cool! Now I wanna make one and add an oven like you talked about.
What’s the compliance range on that?
Ah, I see you used the classic 330R on the LED… Today’s LEDs are far brighter and more efficient — you could drop the current with a 1K or 2K2 and it’d still likely be plenty bright!
What’s the component south of the transistor? 2.6pA