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Constant Current Circuits

#'s - C       DQ      R - S
 

Last Updated: October 24, 2017 02:54 PM

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:

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 Power LoA - D -  Suitable for testing power supplies to 100 watts. __ Designed by Steve Hagerman

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

Constant Voltage-Constant Current Regulator -  With switching frequency as high as 500kHz, The LT®1510 current mode PWM battery charger is the smallest, simplest, most efficient solution to fast-charge modern re-
chargeable batteries including lithium-ion (Li-Ion), nickel-metal-hydride (NiMH
)* and nickel-cadmium (NiCd)* that require constant-current and/or constant-voltage charging.  The internal switch is capable of delivering 1.5A DC current (2A peak current) __ Designed by LT1510/LT1510-5 Application Note

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 David Johnson P.E.-June, 2000

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

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 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

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

 


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