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So I need a component which will have a flat сurrent–voltage characteristic (constant current in a wide voltage range).

Initially I was intended to ask a general question: what kind of the device can do this function. However some of commentators wished more details so I'm putting them into the question:

For the moment I need that the device can be supplied with voltage as low as 1V (I wish it could be even lower) and drive current in scale of tens of microAmsp. The precision of the current should be something within 10% in range of voltage between 1 and 10V and in typical industrial temperature range.

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  • \$\begingroup\$ Saturated transistor? \$\endgroup\$
    – Scott Seidman
    Commented Aug 9, 2016 at 11:15
  • \$\begingroup\$ @ScottSeidman, it will have so big dependence on a temperature, on a manufacturing circumstances and finally I will need an additional current source to the base. I need something precise as zener can do with a voltage. \$\endgroup\$
    – Roman Matveev
    Commented Aug 9, 2016 at 11:18
  • \$\begingroup\$ A constant current diode (or current limit diode). See Wikipedia \$\endgroup\$
    – Steve G
    Commented Aug 9, 2016 at 11:18
  • \$\begingroup\$ @SteveG, so literally it's a combination of depletion mode FET with a resistor? Actually I implemented this schematic for current limiting purposes (basing on BSS126) but the current is widely depend on a Vgs voltage which depends on temperature and other circumstances. So I thought that it is not any precise solution. Is it? \$\endgroup\$
    – Roman Matveev
    Commented Aug 9, 2016 at 11:26
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    \$\begingroup\$ (1) Because the solution will depend on the power level and voltage involved. In your case an opamp might suffice but there's no clue in the original question about whether it's microamps or hundreds of amps, millivolts or kV (wide voltage range). (2) The circuit may be quite simple if the load is a resistor connected to ground. It may be more complex otherwise. I've had the opposite problem to you - I've spent a lot of time answering questions only to find that the OP had left out crucial information that meant my time was wasted. ;^) \$\endgroup\$
    – Transistor
    Commented Aug 9, 2016 at 13:04

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What you are looking for is called a "constant current source". Unfortunately these are not passive components, however luckily they are available in 3 pin IC form that are very easy to implement into your circuit.

Here is an example product: http://uk.rs-online.com/web/p/constant-current-diodes/5359098/

Datasheet: http://www.ti.com/lit/ds/symlink/lm134.pdf

From the data sheet implement it like this:

Constant current source application note.

  • Connect the V+ pin to your supply voltage (it should be quite stable)

  • Connect the R pin to a resistor to V-, the current through the resistor proportionally controls the current out from the output.

  • The output current is provided by V- and the current through the set resistor.

These parts are also available with fixed output currents hardwired into them. They can be slightly cheaper.

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  • \$\begingroup\$ This solution is big and expensive in my case, but it is much better than I had before! Thank you for the idea! \$\endgroup\$
    – Roman Matveev
    Commented Aug 9, 2016 at 11:30
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    \$\begingroup\$ there are very small surface mount versions available, and non programmable versions that are cheaper. have a search around your favourate supplier for whats available. \$\endgroup\$
    – Segfault
    Commented Aug 9, 2016 at 11:32

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