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Circuits designed by David Johnson, P.E.
Last Updated on: Thursday, April 07, 2016 02:04 PM

Master Category List - Dave's Circuits

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Current Source / Current Sink Circuits

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 Dave 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 Dave 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 Dave 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]


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