Difference between revisions of "EEHPRT Simple Low-Current Constant-Current Sources"
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==== Constant-Current Diode ==== | ==== Constant-Current Diode ==== | ||
==== LM134/LM234 | ==== 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!!! | 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 | Total supply voltage range: 1V to 40V | ||
Minimum voltage headroom for regulation: | Minimum voltage headroom for regulation: 1.0V | ||
Current adjustment range: 1μA to 10mA | Current adjustment range: 1μA to 10mA | ||
Minimum regulated current: | Minimum regulated current: 1μA (BS cover sheet claim, too optimistic per rest of datasheet tables and plots) | ||
Maximum regulated current: | Maximum regulated current: 10mA | ||
Maximum voltage delta: | Maximum voltage delta: 40V | ||
Maximum power: | Maximum power: 400mW | ||
Does not require ground reference ("two-terminal" operation)?: Yes | Does not require ground reference ("two-terminal" operation)?: Yes | ||
Accuracy: ±3%. | 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 | |||
==== LM317L ==== | ==== LM317L ==== | ||
Revision as of 23:52, 17 February 2022
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
Constant-Current Diode
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
