2019-11-15 Build A LED Tester

Big Clive’s YouTube video

Ohhh nooo! After all the trouble Big Clive went to show us how a Joule Thief works, he *digressed* to using a 9V battery for his LED tester! Horrors! 😱😱😱

I built a Joule Thief with a socket like he used for the LED. But the JT must not be left open circuited without the LED because the voltage will rise very high and can damage the transistor. So I connected a 6.8V zener in parallel with the socket so the voltage can’t rise above 6.8V. instead of a zener diode, you can use two or three LEDs in series to limit the voltage. When the led is plugged into the socket the 2 LEDs will go dark and the single LED will light up. If the LED is shorted, the two LEDs will go dark, indicating a problem.

One point: the typical 5mm LED and most others, too have a reverse voltage rating of 5V maximum, so if you insert the LED backwards, you are putting over 9V in reverse across the LED. I have never found that the LEDs I’ve tested have been damaged by this, however it is excessive voltage and should not be done.

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