What is the accuracy of LM317 as a cross-current source?

serialworld

What is the accuracy of LM317 as a cross-current source? [Copy link]

I am planning to use LM317 to make a simple cross-current source, 4mA, input voltage 32V, I wonder what the accuracy will be? Working in the temperature range of 0~40 degrees, I wonder if the temperature drift is large? Can I achieve an accuracy of 0.1%?

cruelfox

Do you only make one, or many? The voltage reference of LM317 is discrete. It is easy to make only one. The resistors can be selected and two more can be connected in parallel for fine-tuning. Adjust to the constant current value you want, and then test whether the temperature stability is satisfied. According to your 0.1% requirement, the overall temperature coefficient needs to be within 25ppm/degree (if it is within plus or minus 0.1%, it can be relaxed to 50ppm/degree), which may not be achieved. The resistors also have temperature drift, so actual testing is required.

cruelfox

For 4mA, it is better to use LM334.

maychang

If the constant current is 4mA, LM317 may not work, because its minimum load current requirement is 3.5mA. Using LM317 for 4mA is overkill. It is better to use LM334.

serialworld

maychang posted on 2018-12-31 18:32 If the constant current is 4mA, LM317 may not work, because its minimum load current requirement is 3.5mA. Using LM317 for 4mA is overkill. No...

The minimum current and voltage drop curve on the ST LM317L data sheet seems to be OK for 4mA.

maychang

serialworld published on 2018-12-31 19:05 The minimum current and voltage drop curve on the ST LM317L data sheet seems to be 4mA.

serialworld

cruelfox posted on 2018-12-31 14:18 Do you make just one or many? The voltage reference of LM317 is discrete. It is easy to make just one. The resistor can be selected and two more can be connected in parallel for micro...

I just made one. I happened to have LM317 on hand. In addition, I saw in "Constant Current Source and Its Application Circuit" that LM317 has good performance as a constant current source. So I want to try it.

chunyang

4mA is already critical for LM317. Parameter criticality should be considered unfeasible and a margin should be left in practice.

qwqwqw2088

Constant current source 4mA LM134, LM234, LM334 are all OK. If there is temperature requirement, LM334 is the best one that can meet the requirement, 0C to +70°C