EEHPRT Simple Low-Current Constant-Current Sources - Revision history

21stCP Wiki BDFL at 06:22, 18 February 2022

2022-02-18T06:22:19Z

← Older revision		Revision as of 02:22, 18 February 2022
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	Disadvantages: Not every current choice is available, especially exact selections like 4.0mA. Non-trivial tempco. Shitty datasheet. Large required voltage headroom???		Disadvantages: Not every current choice is available, especially exact selections like 4.0mA. Non-trivial tempco. Shitty datasheet. Large required voltage headroom???

	Since these devices have a shitty datasheet, there is not much more we can determine from the datasheet. Our best understanding of what is inside these devices is that they are simply binned JFETs with controlled gate width/length, and with two terminals interconnected (see ~~<nowiki>~~[[#Single JFET\|section below]]~~</nowiki>~~ on making such a device yourself).		Since these devices have a shitty datasheet, there is not much more we can determine from the datasheet. Our best understanding of what is inside these devices is that they are simply binned JFETs with controlled gate width/length, and with two terminals interconnected (see [[#Single JFET\|section below]] on making such a device yourself).

	==== LM134 / LM234 ====		==== LM134 / LM234 ====

21stCP Wiki BDFL: /* Constant-Current Diode */

2022-02-18T06:21:29Z

Constant-Current Diode

← Older revision		Revision as of 02:21, 18 February 2022
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	Disadvantages: Not every current choice is available, especially exact selections like 4.0mA. Non-trivial tempco. Shitty datasheet. Large required voltage headroom???		Disadvantages: Not every current choice is available, especially exact selections like 4.0mA. Non-trivial tempco. Shitty datasheet. Large required voltage headroom???

	Since these devices have a shitty datasheet, there is not much more we can determine from the datasheet. Our best understanding of what is inside these devices is that they are simply binned JFETs with controlled gate width/length, and with two terminals interconnected (see section below on making such a device yourself).		Since these devices have a shitty datasheet, there is not much more we can determine from the datasheet. Our best understanding of what is inside these devices is that they are simply binned JFETs with controlled gate width/length, and with two terminals interconnected (see <nowiki>[[#Single JFET\|section below]]</nowiki> on making such a device yourself).

	==== LM134 / LM234 ====		==== LM134 / LM234 ====

21stCP Wiki BDFL at 06:16, 18 February 2022

2022-02-18T06:16:53Z

← Older revision		Revision as of 02:16, 18 February 2022
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	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.		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.		Unfortunately, such a part does not really exist if "small" constant current (≤20mA, even more so for ≤10mA) is desired. Several choices are available, each with its own disadvantages or limitations.

			Even less choices are available if adjustment of current output is required, and/or a low tempco (temperature coefficient of changes in output without any adjustment of setpoint) is also needed.

	This article primarily relies on components as currently stocked on DigiKey.		This article primarily relies on components as currently stocked on DigiKey.
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	https://www.digikey.com/en/products/filter/pmic-current-regulation-management/734		https://www.digikey.com/en/products/filter/pmic-current-regulation-management/734

	TODO disclaimer.		TODO DK disclaimer.

	=== Available Component Classes ===		=== Available Component Classes ===
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	===== Single JFET =====		===== Single JFET =====
			[[File:JFET constant-current source.png\|thumb\|JFET constant-current source]]
			A single JFET can be interconnected as shown to make a rather simple constant-current source, which can either be fixed or adjustable.

			The first significant downside is that part selection and binning is required to obtain a particular current value. This is not a problem in a hobby situation, but would be unacceptable in a manufacturing environment.

			Another probable downside is that the voltage regulation overhead would be higher than other solutions shown in this page.

			TODO plot one of these myself!!!

	TODO		TODO
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	Disadvantages:		Disadvantages:

			=== Conclusion ===
			As bizarre as it sounds, few choices exist for simple constant-current regulation below about 10mA, especially if adjustment is required, and tempco must be low. If several considerations are not a deal-killer, the trusty LM317L is probably best. Some solutions exist for niche applications like LED drive, but often have an unacceptably (for many applications) minimum required voltage headroom.

21stCP Wiki BDFL: 21stCP Wiki BDFL moved page EEHPRT Simple Constant-Current Sources to EEHPRT Simple Low-Current Constant-Current Sources without leaving a redirect

2022-02-18T05:44:07Z

21stCP Wiki BDFL moved page EEHPRT Simple Constant-Current Sources to EEHPRT Simple Low-Current Constant-Current Sources without leaving a redirect

← Older revision	Revision as of 01:44, 18 February 2022
(No difference)

21stCP Wiki BDFL: /* LM134 / LM234 */

2022-02-18T05:41:16Z

LM134 / LM234

← Older revision		Revision as of 01:41, 18 February 2022
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	Advantages: Old stuff, small headroom		Advantages: Old stuff, small headroom

	Disadvantages: dependence of current output on IC junction temperature, four components required.		Disadvantages: dependence of current output on IC junction temperature, four components required, adjustable zero-tempco operation is not practical because both resistors' value would have to be adjusted in a tracking manner.

	TODO schematic		TODO schematic

21stCP Wiki BDFL: /* Constant-Current Diode */

2022-02-18T05:36:45Z

Constant-Current Diode

← Older revision		Revision as of 01:36, 18 February 2022
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	==== Constant-Current Diode ====		==== Constant-Current Diode ====
			Constant-current diodes were popular back in the day, but they are relatively rare these days (although LED-drive applications are causing a comeback, even if minimum current regulation for those who bothered to make devices is already too high at 10-20mA for state of the art modern LEDs).

			We will discuss Central Semiconductor Corp CMJ series here, as a representative example for options below 10mA (more options exist for ≥10mA from onsemi et al).

			Total supply voltage range: 50/100V

			Minimum voltage headroom for regulation: On the order of 10V???

			Current adjustment range: --

			Minimum regulated current:

			Maximum regulated current:

			Maximum voltage delta:

			Maximum power: 500mW

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

			Accuracy:

			Reverse-voltage protection?:

			Advantages:

			Disadvantages: Not every current choice is available, especially exact selections like 4.0mA. Non-trivial tempco. Shitty datasheet. Large required voltage headroom???

			Since these devices have a shitty datasheet, there is not much more we can determine from the datasheet. Our best understanding of what is inside these devices is that they are simply binned JFETs with controlled gate width/length, and with two terminals interconnected (see section below on making such a device yourself).

	==== LM134 / LM234 ====		==== LM134 / LM234 ====

21stCP Wiki BDFL: /* LM317L */

2022-02-18T05:13:50Z

LM317L

@@ Line 46: / Line 46: @@
 ==== LM317L ====
 ==== Other Circuits ====
 ==== Discrete Circuits ====

21stCP Wiki BDFL: /* LM134/LM234/LM334 */

2022-02-18T04:52:31Z

LM134/LM234/LM334

← Older revision		Revision as of 00:52, 18 February 2022
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	==== Constant-Current Diode ====		==== Constant-Current Diode ====

	==== LM134/LM234~~/LM334~~ ====		==== 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 ====

21stCP Wiki BDFL: /* LM134/LM234/LM334 */

2022-02-18T04:42:30Z

LM134/LM234/LM334

← Older revision		Revision as of 00:42, 18 February 2022
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	==== LM134/LM234/LM334 ====		==== LM134/LM234/LM334 ====
			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:

			Current adjustment range: 1μA to 10mA

			Minimum regulated current:

			Maximum regulated current:

			Maximum voltage delta:

			Maximum power:

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

			Accuracy: ±3%.

	==== LM317L ====		==== LM317L ====

21stCP Wiki BDFL at 04:32, 18 February 2022

2022-02-18T04:32:43Z

@@ Line 3: / Line 3: @@
 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.
 === Available Component Classes ===
 ==== Constant-Current Diode ====