EEHPRT Simple Low-Current Constant-Current Sources

Introduction

Whether driving LEDs or for transducer excitation, a need arises for a simple (ideally, two-leaded part) constant-current source which is simple to use, compact, versatile, adjustable, and has a wide span of current adjustment and excitation voltage supply range.

Unfortunately, such a part does not really exist if "small" constant current (<20mA) is desired. Several choices are available, each with its own disadvantages or limitations.

This article primarily relies on components as currently stocked on DigiKey.

https://www.digikey.com/en/products/filter/pmic-current-regulation-management/734

TODO disclaimer.

Available Component Classes

LM134 / LM234

LM134/LM234/LM334 is a strange old device, in that its current is highly dependent on IC junction temperature. With an added diode and resistor, at total component count of four devices, tempco can be minimized but NOT eliminated to the point of acceptable standards in modern times. We suppose this device still has archaic use cases. We wish there was its equivalent with zero tempco by now!!!

Total supply voltage range: 1V to 40V

Minimum voltage headroom for regulation: 1.0V

Current adjustment range: 1μA to 10mA

Minimum regulated current: 1μA (BS cover sheet claim, too optimistic per rest of datasheet tables and plots)

Maximum regulated current: 10mA

Maximum voltage delta: 40V

Maximum power: 400mW

Does not require ground reference ("two-terminal" operation)?: Yes

Accuracy: ±3%.

Reverse-voltage protection?: Yes

Advantages: Old stuff, small headroom

Disadvantages: dependence of current output on IC junction temperature, four components required.

TODO schematic

TODO modern diode