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Constant Current Circuits

#'s - C       DQ      R - S
 

Last Updated: December 31, 2017 06:47 AM

Circuits Designed by Dave Johnson, P.E.

1 Amp Current InjectorI designed and built this thing many years ago.  I published the hobby circuit in the now defunct “Radio Elecronics” magazine back in 1992.  The electronic circuit injects a precise 1 amp of current into any unknown resistor, up to about two ohms.  Two alkaline C cells power the complete circuit.. . . Circuit by David Johnson P.E.-July, 2006

100ma Current SourceOften in industrial control systems a constant current source is needed, which is controlled by a computer and referenced to circuit ground.  The circuit below converts a zero to 5v signal from a computer’s analog output into a current, with a full scale of 100ma.  The circuit shown requires a 9v DC supply. . . Circuit by David Johnson P.E.-July, 2008

6v NMH/NiCd Battery TesterI designed this circuit to test rechargeable six volt battery packs under constant current conditions.  As designed, the circuit applies a 10 amp load to the battery pack.  A heat sink must be used on the main power transistor. . . Circuit by Dave Johnson P.E.-December, 2004

Computer Controlled 100ma Current SourceOften in industrial control systems a constant current source is needed, which is controlled by a computer and referenced to circuit ground.  The circuit below converts a zero to 5v signal from a computer’s analog output into a current, with a full scale of 100ma.  The circuit shown requires a 9v DC supply. . . Circuit by David A. Johnson P.E.-July, 2008

Constant Current Drives LEDsLEDs are current driven devices.  The light they produce is proportional to the current flowing though them.  One way to maintain a fairly steady light output is to keep the current through the LED fixed, even as the supply voltage may change.  A classic . . . Hobby Circuit designed by David A. Johnson P.E.-December, 2010

Constant Current LED DriverBob Pease from National Semiconductor came up with this circuit and I have used it many times.  It maintains a constant current through one or more LEDs.  A single resistor controls the desired current. . . . Hobby Circuit designed by David A. Johnson P.E.-November, 2004

Current InjectorWhen you need to measure resistance down to a few micro ohms, this circuit works great.  It is powered from two "C" cell batteries and is designed to inject a well regulated one amp of current into the unknown resistance.  By measuring the voltage drop across the resistor with a digital voltmeter, the resistance value can be accurately measured.  The circuit also is equipped with a low battery monitor.  Published in Popular Electronics, November 1992modified on July 11, 2006. . . Circuit by David Johnson P.E.-June, 2000

Current Source is Computer ControlledOften in industrial control systems a constant current source is needed, which is controlled by a computer and referenced to circuit ground.  The circuit below converts a zero to 5v signal from a computer’s analog output into a current, with a full scale of 100ma.  The circuit shown requires a 9v DC supply . . . Hobby Circuit designed by Dave Johnson P.E.-July, 2008




Links to electronic circuits, electronic schematics, designs for engineers, hobbyists, students & inventors:

±5A, 2.5V (2-Quadrant) μModule Voltage Regulator -  The LTM8052 is a 36VIN, 5A, 2-quadrant constant-voltage, constant-current   (CVCC) step-down μModule® regulator.  Included in the package are the switching controller, power switches, inductor and support components.  Operating over an input voltage range of 6V to 36V, the LTM8052 supports an output voltage range of 1.2V to 24V. __ Linear Technology/Analog Devices App Note, Mar 30th 2012

0A to 2A Current Source -  The LT1995 amplifies the sense resistor drop by 5V/V and subtracts that from VIN, providing an error signal to an LT1880 integrator.  The integrated error drives the PMOSFET as required to deliver the commanded current. __ Linear Technology/Analog Devices App Note,

1 Amp Current Injector -  I designed and built this thing many years ago.  I published the hobby circuit in the now defunct “Radio Elecronics” magazine back in 1992.  The electronic circuit injects a precise 1 amp of current into any unknown resistor, up to about two ohms.  Two alkaline C cells power the complete circuit.. . . Circuit by David Johnson P.E.-July, 2006

100ma Current Source -  Often in industrial control systems a constant current source is needed, which is controlled by a computer and referenced to circuit ground.  The circuit below converts a zero to 5v signal from a computer’s analog output into a current, with a full scale of 100ma.  The circuit shown requires a 9v DC supply. . . Circuit by David Johnson P.E.-July, 2008

2-Terminal 3A Current Source -  The LT3083 is a 3A low dropout linear regulator that can be paralleled to increase output current or spread heat on surface mounted boards.  Architected as a precision current source and voltage follower, this new regulator finds use in many applications requiring high current, adjustability to zero, and no heat sink.  The device __ Linear Technology/Analog Devices App Note, Mar 9th 2011

2-Terminal Temperature-to-Current Thermometer Suitable for Use at the End of Long Wire Runs -  By adding the LT3092 to a thermistor kit along with three 0.1% accuracy resistors and one final trim, a very accurate 2-terminal temperature-to-current converter can be built.  This circuit measures 700μA operating current at 0°C, dropping by 2μA every degree until 100°C, at which point the current measures 500μA.  The obvious __ Linear Technology/Analog Devices App Note, Oct 26th 2010

3-transistor current source covers wide range -  05/31/14  EDN-Design Ideas This Design Idea is a two-wire current regulator that strikes a good balance between performance and parts count.  Employing three transistors, three resistors, and one LED, it achieves good regulation   (better than 1% over most of the voltage range), lower operating voltage   (1.2V typical), and better tempco   (0.07%/K) than other circuits of similar complexity.  It is designed to operate in a range of currents from tens of milliamperes to several amps.  It does not use any hard to find parts; for example: an LM10 can be used to make an even higher performance circuit, but this IC is not multi-sourced and is likely to be discontinued.  __ Circuit Design by Einar Abell0

6v NMH/NiCd Battery Tester -  I designed this circuit to test rechargeable six volt battery packs under constant current conditions.  As designed, the circuit applies a 10 amp load to the battery pack.  A heat sink must be used on the main power transistor. . . Circuit by Dave Johnson P.E.-December, 2004

A Compendium of Pleasant Current Events -  Linear Technology AN90 __ Designed by Jim WilliamsApr 1st, 2002

Achieve Constant Current Over Wide Range of Terminal Voltages -  11/04/10 EDN-Design Ideas Eliminate errors caused by bias currents and temperature drifts.  __ Circuit Design by Donald Boughton, Jr, International Rectifier, Orlando, FL

Adjustable Two Terminal 200mA Current Source -  The LT3092 requires only two resistors to set the current between 0.5mA and 200mA __ Linear Technology/Analog Devices App Note, Mar 24th 2010

AN90Current Sources for Fiber Optic Lasers: A Compendium of Pleasant Current Events -  Linear Technology AN90 __ Designed by Jim WilliamsApr 1st, 2002

AN92Bias Voltage and Current Sense Circuits for Avalanche Photodiodes -  Linear Technology AN92 __ Designed by Jim WilliamsNov 1st, 2002

Bidirectional Current Source -  The LT1990 is a differential amplifier with integrated precision resistors.  The circuit shown is the classic Howland current source, implemented by simply adding a sense resistor. __ Linear Technology/Analog Devices App Note, Mar 31, 2010

Bipolar current source maintains high output impedance at high frequencies -  12/05/05 EDN-Design Ideas Use line-receiver/amp ICs to build high-frequency constant-current sources__ Circuit Design by Alex Birkett, University College London, Hospital National Health Service, London, UK

Build a precise DC floating-current source -  08/18/05 EDN-Design Ideas Use a general impedance converter and resistors to develop a specialized current source__ Circuit Design by D Ramírez, S Casans, C Reig, AE Navarro, and J Sánchez, University of Valencia, Burjassot, Spain

Choose Resistors to Minimize Errors in Grounded-Load Current Source -  EDN  How to Article-April 19, 2013    Operational amplifiers are frequently used to make high-quality current sources in a variety of applications, such as industrial process control, scientific instrumentation, and medical equipment.  Single Amplifier Current Sources, published in Analog Dialogue, Volume 1, Number 1, 1967, introduces several current source circuits that provide a constant current through floating loads or grounded loads.  In industrial applications, such as pressure transmitters and gas detectors, these circuits are widely used to provide 4 mA to 20 mA or 0 mA to 20 mA currents.  __ Circuit Design by David Guo

Circuit Achieves Constant Current Over Wide Range Of Terminal Voltages -  11/04/10 EDN-Design Ideas Eliminate errors caused by bias currents and temperature drifts.  __ Circuit Design by Donald Boughton, Jr, International Rectifier, Orlando, FL

Circuit forms constant-current SCR -  02/01/01 EDN-Design Ideas A typical SCR (silicon-controlled rectifier) requires a trigger current, which causes the SCR structure to latch on.  Once the device latches, the current through the SCR is solely a function of external component values.  The SCR has no inherent ability to limit the current flow once it latches on.  Current continues to flow, as long as the current exceeds a minimal value known as the holding current.  The circuit in Figure 1 is similar to an SCR, because it also requires a trigger current to latch into its on state.   __ Circuit Design by Robert Buono, Ringwood, NJ

Circuit Forms Novel Floating Current Source -  1-May-03 EDN-Design Ideas One-shot provIdeas frequency discriminationFigure 1 shows a polarization circuit applicable to ISFET(ion-sensitive field-effect-transistor] sensors.  ISFETs are solid-state chemical sensors that measure the pH value of a solution in biomedical and environmental applications, for example.  The circuit in Figure 1 is extremely simple; it sets fixed-bias conditions for ISFET sensors(VDS=I0 RX; IDS=I0]__ Circuit Design by S Casans, AE Navarro, and D Ramirez, University of Valencia, Burjassot, Spain

Circuit provides constant current for ISFETs/MEMFETs -  26-Oct-00 EDN-Design Ideas ISFETs and MEMFETs(ion-sensitive and membrane FETs] are solid-state chemical sensors that provide an electrical signal associated with the change of a.   [Pdf contains several circuits, scroll to find this one.   __ Circuit Design by S Casans, D Ramirez, and AE Navarro, University of Valencia, Burjassot, Spain

Circuit provides constant-current load for testing batteries -  26-Oct-00 EDN-Design Ideas ISFETs and MEMFETs(ion-sensitive and membrane FETs] are solid-state chemical sensors that provide an electrical signal associated with the change of a.   [Pdf contains several circuits, scroll to find this one.   __ Circuit Design by S Casans, D Ramirez, and AE Navarro, University of Valencia, Burjassot, Spain

Circuit provides efficient fan-speed control -  4-Mar-04 EDN-Design Ideas As Moore's Law plunges us into the realm of multigigahertz processors and PCs with gigabytes of RAM, engineers face the task of removing the heat that these state-of-the-art components produce.  Cooling such systems poses a dilemma.  If you optimize the fan size and speed for nominal operating conditions, the system is susceptible to failure when conditions deteriorate__ Circuit Design by John Guy, Maxim Integrated Products, Sunnyvale, CA

Circuit Provides Motor Feed Control -  07/25/02 EDN-Design Ideas Linear power driver works from single supplyBecause we needed a small grinding machine, we modified an old milling machine that lacked a control system.  The table of the grinding machine needed only to move back and forth with__ Circuit Design by Jean-Bernard Guiot

Computer Controlled 100ma Current Source -  Often in industrial control systems a constant current source is needed, which is controlled by a computer and referenced to circuit ground.  The circuit below converts a zero to 5v signal from a computer’s analog output into a current, with a full scale of 100ma.  The circuit shown requires a 9v DC supply. . . Circuit by David A. Johnson P.E.-July, 2008

Constant Current Battery Charger -  A simple method of charging a battery from a higher voltage battery is shown in the circuit below to the left.  Only one resistor is needed to set the desired charging current and is calculated by dividing the difference in battery voltages by the charge current.  So, for example if 4 high capacity (4000 mA hour) ni-cads are to be charged at 300 mA from a 12 volt battery, the resistor need, __ Designed by Bill Bowden

Constant Current Charger -  This simple constant current source uses an LM317 regulator IC.  N.  B.  The pin-outs of the IC are not a mistake, the output is taken from the adjustment pin.  I found this circuit to charge all my NiCad batteries, and I use a Kambrook mechanical light-timer (or equiv.) for 110vac to time the charge __ Designed by John Nooyen

Constant Current Drives LEDs -  LEDs are current driven devices.  The light they produce is proportional to the current flowing though them.  One way to maintain a fairly steady light output is to keep the current through the LED fixed, even as the supply voltage may change.  A classic . . . Hobby Circuit designed by David A. Johnson P.E.-December, 2010

Constant Current for ISFETs/MEMFETs -  26-Oct-00 EDN-Design Ideas ISFETs and MEMFETs(ion-sensitive and membrane FETs] are solid-state chemical sensors that provide an electrical signal associated with the change of a.   [Pdf contains several circuits, scroll to find this one.   __ Circuit Design by S Casans, D Ramirez, and AE Navarro, University of Valencia, Burjassot, Spain

Constant Current LED Driver -  Bob Pease from National Semiconductor came up with this circuit and I have used it many times.  It maintains a constant current through one or more LEDs.  A single resistor controls the desired current. . . . Hobby Circuit designed by David A. Johnson P.E.-November, 2004

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Constant Current Circuits:  #'s - C       DQ      R - S


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