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Constant Current Circuits
Last Updated on: Friday, August 21, 2015 06:59 AM

Circuits Designed by Dave Johnson, P.E. :
  • 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.,  07/11/06]

  • 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.,  07/09/08]

  • 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.,  12/12/04]

  • 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.,  07/09/08]

  • 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.,  12/13/10]

  • 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.,  11/25/04]

  • Current Injector -  When 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 1992 - modified on July 11, 2006  . . . [Circuit by David Johnson P.E.,  06/04/00] 

  • Current Source is Computer Controlled -  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 . . . [Hobby Circuit designed by Dave Johnson P.E.,  07/08/08] 

  • Ground Resistance Tester -  UL requires that an electrical system using a metal chassis earth ground connection have a resistance of less than 0. 1 ohms.   This resistance must be tested with actual line current in excess or 10 Amps.   The circuit shown uses a couple of LEDs to indicat . . . [Hobby Circuit designed by Dave Johnson P.E.,  04/28/01]

  • LED Driver using Constant Current -  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 . . . [Circuit by Dave Johnson P.E.,  12/13/10]

  • NMH/NiCd 6v 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 . . . [Hobby Circuit designed by David A. Johnson P.E.,  12/12/04]

  • One 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 . . . [Hobby Circuit designed by David A. Johnson P.E.,  07/11/06]

  • Test UL Ground Resistance -  UL requires that an electrical system using a metal chassis earth ground connection have a resistance of less than 0. 1 ohms.  This resistance must be tested with actual line current in excess or 10 Amps.   The circuit shown uses a couple of LEDs to indicate . . . [Circuit by David Johnson P.E.,  04/28/01] 

  • Tests UL Ground Resistance -  UL requires that an electrical system using a metal chassis earth ground connection have a resistance of less than 0. 1 ohms. This resistance must be tested with actual line current in excess or 10 Amps. The circuit shown uses a couple of LEDs to indicate if in fact the resistance is less than 0. 1 ohms - modified on july 10, 2006 . . . [Hobby Circuit designed by Dave Johnson P.E.,  04/28/01]

  • UL Ground Resistance Tester -  UL requires that an electrical system using a metal chassis earth ground connection have a resistance of less than 0. 1 ohms. This resistance must be tested with actual line current in excess or 10 Amps. The circuit shown uses a couple of LEDs to indicate if in fact the resistance is less than 0. 1 ohms - modified on July 10, 2006 . . . [Circuit by David Johnson P.E.,  04/28/01]


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 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 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.,  07/11/06]

 

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.,  07/09/08]

 

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 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 App Note - , Oct 26th 2010]

 

3-transistor current source covers wide range -  05/31/14  EDN Design Idea   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. . . .  [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.,  12/12/04]

 

Achieve Constant Current Over Wide Range of Terminal Voltages -  11/04/10 EDN Design Idea   Eliminate errors caused by bias currents and temperature drifts. . . .  [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 App Note - , Mar 24th 2010]

 

AN-D16: LND1 Series: Constant Current Sources And -  Supertex Semiconductors. . . 

 

AN-D18: DN25 Series: Constant Current Sources And -  Supertex Semiconductors. . . 

 

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 App Note - , Mar 31, 2010]

 

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

 

Build a precise DC floating-current source -  08/18/05  EDN Design Idea   Use a general impedance converter and resistors to develop a specialized current source. . .  [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 -  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. . . .  [EDN  How to Article by David Guo -April 19, 2013]

 

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

 

Circuit forms constant-current SCR -  02/01/01 EDN Design Idea   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. . .  [by Robert Buono, Ringwood, NJ ]

 

Circuit Forms Novel Floating Current Source -  05/01/03  EDN Design Idea   One-shot provides frequency discrimination - Figure 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 i. . .  [by S Casans, AE Navarro, and D Ramirez, University of Valencia, Burjassot, Spain]

 

Circuit provides constant current for ISFETs/MEMFETs -  10/26/00  EDN Design Idea   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. . . .  [by S Casans, D Ramirez, and AE Navarro, University of Valencia, Burjassot, Spain]

 

Circuit provides constant-current load for testing batteries -  02/19/09  EDN Design Idea   A 9V battery provides power for a constant-current source for testing AA- or AAA-size batteries. . .  [by Vladimir Rentyuk, Modul-98 Ltd, Zaporozhye, Ukraine]

 

Circuit provides efficient fan-speed control -  03/04/04  EDN Design Idea   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. . . .  [by John Guy, Maxim Integrated Products, Sunnyvale, CA]

 

Circuit Provides Motor Feed Control -  07/25/02 EDN Design Idea   Linear power driver works from single supply - Because 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. . .  [by Jean-Bernard Guiot]

 

Complete Monolithic Current Transmitter -  PDF contains several designs, scroll to find this one. . .  [Analog Devices-Analog Dialogue by Bruce, Ian]

 

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.,  07/09/08]

 

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, . . .  [Bill Bowden's website]

 

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Constant Current Circuits


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