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Current Source / Current Sink Circuits

Current Source Circuits:  #'s - B       C - G       H - S      T - Z
 

Last Updated: December 07, 2017 02:04 PM

Circuits Designed by Dave Johnson, P.E.

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 Dave 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

Ground Resistance TesterUL requires that an electrical system using a metal chassis earth ground connection have a resistance of less than 0.1ohms.    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.-April, 2001


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

Cascode Current Source  -  Circuit Ideas for Designers App Note___ Advanced Linear Devices, Inc

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 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

CMOS Buffer Delivers Precise Current Pulse -  12/08/94 EDN-Design Ideas The circuit in Fig 1 delivers stable, fast-settling reference-current pulses.  You can use the circuit in systems employing A/D, D/A, or V/F converters.  Digital input pulses, VP, connect to IC3B, a 74AC240 buffer.  The 5.00V reference, IC1, constrains IC3B's output, VR, to either VREF or0V.  IC3B's rise and fall times are <3 nsec__ Circuit Design by Hartmut Henkel, Consultant, Kriftel, Germany

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

Constant current LED driver using an NPN transistor to control an N-channel MOSFET -  Here's a really simple and inexpensive ($1) LED driver circuit.  The circuit is a "constant current source", which means that it keeps the LED brightness constant no matter what power supply you use or surrounding environmental conditions you subject the LED's to. __

Constant current LED driver using LM334 plus a transistor -  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. __ Designed by David Johnson, Discovercircuits.com May, 2006

Constant current, constant voltage converter drives white LEDs -  09/02/04  EDN-Design Ideas LEDs usually take their drive from a constant dc-current source to maintain constant luminescence.  Most DC/DC converters, however, deliver a constant voltage by comparing a feedback voltage to an internal reference via an internal error amplifier.  The easiest way to turn a simple DC/DC converter into a constant-current source is to use a sense resistor to convert the output current to a voltage__ Circuit Design by Keith Szolusha, Linear Technology Corp, Milpitas, CA

Constant High-Current Source -  A companion project to last month's stepper motor controller, this simple high-current source can also charge batteries.___ SiliconChip

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 1992modified on July 11, 2006. . . Circuit by Dave Johnson P.E.-June, 2000

Current Regulators -  I have been asked a couple times about constant current regulators.  Here are a couple simple ones.   Set R2 on both circuits for 0.6 volts at the desired current.  Select Q1 and select R1 according to the amount of current you would like to source or limit.  (__ Designed by Andrew R. Morris

Current Source -  Getting optimum performance in certain applications requires that some components, sensors, DC motors, transistors, be driven or biased by a constant current.  We're mostly familiar with voltage regulators and their ability to maintain a constant voltage under varying current conditions.  In this application, your challenge is to provide a constant (spice design)  __

Current source allows measuring three-wire RTD -  07/06/00 EDN-Design Ideas In applications in which you need remote measurement of temperature with a three-wire RTD (resistance-temperature detector), it is important to eliminate the ohmic errors caused by the excitation current flowing through the wiring resistance.  You can locate the RTD more than 1000 ft from the ADC with wiring resistance in the tens of ohms.   __ Circuit Design by John Wynne, Analog Devices, Limerick, Ireland

Current source forms unusually Simple Circuit regulator -  09/12/97 EDN-Design Ideas Simple regulator uses a switching current source to drive a pair of shunt Zener regulators, circuit produces ±15V dual outputs, for total output power of approximately400 mW form100-400-Volt DC source__ Circuit Design by Kennan Herrick, ESI Electronics, San Francisco, CA

Current source has high compliance -  09/01/00 EDN-Design Ideas Current sources are useful in many areas of electronics, such as voltage and current division, current transmitters, excitation of thermistors, RTDs, bridges, potentiometers, and circuit biasing.  Current sources are either fixed- or adjustable-current types.  For the dual-op-amp current source in Figure 1 , the load current, I L , is adjustable by varying V IN (0 to±1.  __ Circuit Design by Frank Vitaljic, Bellingham, WA

Current source has high output impedance -  06/22/00  EDN-Design Ideas A reference current source needs high accuracy, low temperature drift, and high output impedance.  Available IC current sources come with some of these features.  However, at current levels greater than 1 mA, their output impedance decreases to less than 10 MW.  Figure 1 shows a composite 10-mA current-source configuration that has a compliance voltage of 5 to 42V, a set-current error of less than 1%, a temperature drift of less than 45 ppm/°C, and an output impedance of greater than 100 MW.  __ Circuit Design by Clayton B Grantham, National Semiconductor, Tucson, AZ

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.-July, 2008

Current Source Makes Novel Class a Buffer -  3-Apr-08 EDN-Design Ideas A pair of classic current sources in totem-pole configuration enables a novel Class A buffer__ Circuit Design by Horst Koelzow, Winnipeg, MB, Canada

Current Source Mirror -  Circuit Ideas for Designers App Note___ Advanced Linear Devices, Inc

Current Source Multiplication -  Circuit Ideas for Designers App Note___ Advanced Linear Devices, Inc

Current Source with Gate Control -  Circuit Ideas for Designers App Note___ Advanced Linear Devices, Inc

Current sources & mirrors -  There are many useful circuit elements: current sources and current mirrors are two of them.  Sources and mirrors are so closely related that it is sometimes difficult to differentiate between them.  So what?labelling things is a function of language not of electronics!  __ Designed by Richard Torrens

Current Sources for Fiber Optic Lasers -  Linear Technology AN90 __ Designed by Jim WilliamsApr 1st, 2002

Current Sources for Fiber Optic Lasers -  AN90 A large group of fiber optic lasers are powered by DC current.  Laser drive is supplied by a current source with modulation added to the signal.  The current source, although conceptually simple, constitutes an extraordinarily tricky design problem.  There are a number of practical requirements for a fiber optic current source and failure to consider them can cause laser and/or optical component destruction.  This App Note describes ten laser current source circuits with a range of capabilities.  High and low current types are presented, along with designs___ Linear Technology/Analog Devices

Current sources for fiber-optic lasers: a compendium of pleasant current events -  08/22/02  EDN Technical Article: It takes an aura of thoughtful caution to design a laser current source.  A range of circuits that use linear and switched-mode techniques shows how.  __ Circuit Design by Jim Williams, EDN's most revered contributor, passed away in June 2011 after a stroke.  He was 63.

Current-source & Sinks Have Low TC -  07/04/96 EDN-Design Ideas Most current-source and -sink circuits are either simple, precise, or low dropout.  The circuits in Figure 1 have the advantage of all three features and are also switchable.  Figure 1a was originally intended for the current-source side of an H-bridge drive for spacecraft torque rods.  Thus, high-reliability and radiation-tolerant components are not necessary.   __ Circuit Design by Carl R Anderson, Ball Aerospace, Boulder, CO

Current-source enables op Amp's output to go to ground -  5-Aug-04 EDN-Design Ideas The LM324 is a cost-effective choice for an op amp, especially when you need to apply ground-level inputs.  Although its output purportedly includes ground, its poor current-sinking capability limits the applications.  At output voltages lower than 0.5V, the op amp's sinking current ranges only from 2 to 100 µA__ Circuit Design by Frank Chan, Vancouver, BC, Canada

Current-source is nonvolatile -  02/07/02  EDN-Design Ideas Digitally programmable current sources that feature automatic trimming and retain the setting despite power-down cycles are useful in applications such as RF- and laser-communications drivers.  The circuit in Figure 1, for example, i__ Circuit Design by Stephen Woodward, University of North Carolina, Chapel Hill

DAC & flip-flops form constant-current-source -  23-Apr-09 EDN-Design Ideas Using two flip flops, you can program a serial-input DAC to produce a constant 4 mA__ Circuit Design by Marián Štofka, Slovak University of Technology, Bratislava, Slovakia

DAC Controlled 100mA Current Source -  The LT3092 easily interfaces with an external DAC to allow digital current control.  __ Linear Technology/Analog Devices App Note, Mar 24th 2010

Data switch & indicator, bi-directional -  This is a very simple circuit to interface a current loop sensor to an input which is designed for a voltage, such as that from a standard potentiometer.  This page is technical so that interested persons can build the circuit themselves, but 4QD can also supply the interface on a 'postage stamp' sized (22mm x 27mm) board as shown in the first diagram.  It is a relatively trivial circuit! __ Designed by Richard Torrens

DC Voltage & Current Source -  A reference volatge and current source for testing data converter and analog amplifier.  A simple circuit built with TI LinCMOS opamp, TLC254C provides multiple outputs: +2.5V, 0 to +2.5V and 0 to 250uA.  The circuit is operated with 9V battery. __ Designed by Wichit Sirichote

Derive a Simple Circuit High-Current Source From a LAB Supply -  16-Oct-08 EDN-Design Ideas With a few additional components, you can configure a laboratory power supply as a high-current source__ Circuit Design by Roger Griswold and Alfredo Saab, Maxim Integrated Products, Sunnyvale, CA

Design Formulas Simplify Classic V/I Converter -  01/20/00 EDN-Design Ideas Figure 1 shows a classic voltage-to-current (V/I) converter.  You can select the resistor values such that the output current in the load, R L , varies only with the input voltage, V IN , and is independent of R L .  The circuit is widely used in industrial instruments for supplying a 4- to 20-mA signal.  __ Circuit Design by Dudley Nye

Digital current-source is nonvolatile -  02/07/02  EDN-Design Ideas Digitally programmable current sources that feature automatic trimming and retain the setting despite power-down cycles are useful in applications such as RF- and laser-communications drivers.  The circuit in Figure 1, for example, i__ Circuit Design by Stephen Woodward, University of North Carolina, Chapel Hill

Dual Constant-Current Load Tests Low-Current Power Supplies -  06/07/07 EDN-Design Ideas You can use a simple 9V-battery-powered constant-current load to test small power supplies at various loads.  Today’s small electronic appliances, such as washers, dryers, and stoves, use switched-mode power supplies to replace bulky, heavy, linear-power supplies.  The engineer testing these power supplies, which range in current from 50 mA to 1A, typically uses resistors or standard off-the-shelf electronic loads.  An engineer would employ a variety of high-wattage resistors to verify multiple loading conditions to satisfy a proper design.  Most off-the-shelf electronic loads target an average of 300W.  When measuring 50 to 300 mA, a display is inaccurate; most of them display 0.1A, but accuracy is questionable at that low range.  You can alternatively use the simple dual constant-current-load design in Figure 1, which you can build with inexpensive, common parts.  __ Circuit Design by John Lo

Error compensation improves bipolar-current sinks -  07/06/06 EDN-Design Ideas Circuit compensates for pass-transistor's base-current error__ Circuit Design by Christian de Godzinsky, Planmeca Oy, Helsinki, Finland

Ground Referred Precision Current Sources -  The zero drift LTC2054 instrumentation amplifier can be used in conjunction with one of Linear Technology's precision, low temperature drift shunt voltage references (in this example the LT1634) to create a precision, ground referred current source.  ___ Linear Technology/Analog Devices App Note, Mar 30th 2010

Ground Resistance Tester -  UL requires that an electrical system using a metal chassis earth ground connection have a resistance of less than 0.1ohms.    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.-April, 2001


Current Source Circuits:  #'s - B       C - G       H - S      T - Z


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