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1 AMP 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
4 – 20ma Current Loop Tester This circuit injects an adjustable current through a wire loop.
Using a digital current meter, the current can be adjusted from near zero to over 24
milliamps.
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.
Computer
Controlled 100ma Current Source(July 11, 2008) 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 but any voltage from 9v to 12v will
work.
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.
Constant Current LED Driver 5
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 way to
do this is shown below. This works fairly well but it has two weaknesses.
