TRANSISTOR TESTER Circuit
The 555 operates at
2Hz. Output pin 3 drives the circuit with a positive then zero
voltage. The other end of the circuit is connected to a voltage
divider with the mid-point at approx 4.5v. This allows the red and
green LEDs to alternately flash when no transistor
is connected to the tester.
If a good transistor is connected, it will produce a short across
the LED pair when the voltage is in one direction and only one LED
will flash. If the transistor
is open, both LED�s will flash and if the transistor is
shorted, neither LED will flash.
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