This simple LED tester consists of a current source with a potentiometer
that can be used to adjust the current. The current source is
implemented using a type TL081 opamp. The output current of the opamp
flows through the diode and R2. The voltage drop across R2 is fed back
to the inverting input and compared with the reference voltage, which is
set with R1 and applied to the non-inverting input. The adjust- ment
range is approximately 0–30 mA, which is suitable for testing all normal
LEDs. If you wish, you can connect a multi- meter across the LED to
measure the voltage on the LED. For the power source, a good option is
to use a small laboratory power supply with the output voltage set to 5
V. It is convenient to fit the potentiometer with a scale so you can see
directly how much current is flowing through the LED. In order to
calibrate the scale, you can temporarily connect an ammeter in place of
the LED.
schematic |
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