op-amp replacement

Question

I am trying to built this current source, but he LM107 seems to be discontinued, what opamp could I replace it with? I dont know much about opamps and there are so many choices.

Any maybe an opinion on updating the other components as well would be nice, they seem hard to find.

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Maybe some of the answers to [“Standard” components…?](http://electronics.stackexchange.com/q/83580/2191) will help? — RedGrittyBrick, Jan 23 '14 at 16:33
You can probably replace the JFET / bipolar combo with a single MOSFET. Is your control voltage really negative? And your load connected to negative voltage? — markrages, Jan 23 '14 at 16:46
Then consider this current source: http://electronics.stackexchange.com/a/1075/411 — markrages, Jan 23 '14 at 17:02

score 2 · Accepted Answer · answered Jan 23 '14 at 17:38

2

The lazy approach would be: -

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You can find all their integrated current sources here

answered Jan 23 '14 at 17:38

Andy aka

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score 1 · Answer 2 · answered Jan 23 '14 at 16:34

Any general purpose op-amp with low enough Vos for your accuracy requirements should work.

The output current error will be roughly \$V_{os}\mathrm{R_1}\$.

So go to your favorite op-amp vendor, like TI, Analog, or Linear Technology. Use their parametric search tool and sort by price.

Find the lowest-cost part with Vos low enough to meet your accuracy requirements.

Also be sure to consider the temperature coefficient of Vos (if you need accuracy over temperature) and whether the part works with the suppply voltages you have available.

I am thinking of using this guy http://www.digikey.ca/product-detail/en/TLE2141IP/296-10458-5-ND/380981 — jkozlowski, Jan 23 '14 at 16:45

Spehro Pefhany · Answer 3 · 2014-01-23T21:30:36.010

You will need to use an amplifier that has a low enough input offset current and input offset voltage. To use that circuit, the input bias current should be much lower than your desired output current, and the offset voltage should be much greater than the output current multiplied by R1. The definition of "much" depends on your desired accuracy.

Op-amp input bias current causes a direct 1:1 error in the output current of the circuit \$e_{I_{ib}} = I_b\$, and offset voltage represents an error of \$e_{V_{os}} = \$\$V_{os} \over R_1\$.

JFET gate leakage will also add a small error, usually well under 1nA at room temperature (40pA maximum @25°C in the case of the 2N3456).

You could try to substitute a MOSFET in the circuit, however you are likely to have stability issues if the MOSFET is large and the value of R1 is less than about 100 ohms. Normally we'd do an "inside the loop" compensation to provide a separate AC feedback path so the gate capacitance doesn't cause oscillation.

One "general purpose" precision op-amp that would be good for this sort of thing is the OPA277, about $2.50 in small quantities. It has < 50uV \$V_{os }\$, low \$TCV_{os}\$, high gain, and bias current of only a few nA over temperature.

op-amp replacement

3 Answers3