Jun 032016
 

Semiconductor diode tester circuit using 741 IC

This semiconductor diode tester circuit using a 741 IC, can test whether a semiconductor diode is in good condition and also determines its polarity.

How the Semiconductor diode tester circuit works?

To accomplish this, the operational amplifier (IC1) is configured as an oscillator, using R1, R2, R3 resistors and capacitor C1.

At the output of operational amplifier we have a square wave, which will make the D2 and D3 LEDs turn on and off indicating a state of the semiconductor diode under test.

The diode to be tested is placed between test points A and B, as shown in the circuit diagram.

Semiconductor diode tester circuit using 741 IC

First case: When the diode under test is connected cathode to point B and anode to point A.

  • When the oscillator output is at high voltage level, the semiconductor diode under test must be forward biased and consequently the D3 LED should light.
  • When the oscillator output is at low voltage level, the semiconductor diode under test, will be polarized in reverse and as a result no LED should light.

Second case: When the diode under test is connected cathode to point B and anode to point A.

  • When the oscillator output is at high level, the semiconductor diode under test must be reverse biased and no LED should light.
  • When the oscillator output is at low voltage level, the semiconductor diode under test, will be forward biased and consequently D2 LED lights.

If the semiconductor diode under test meets the above conditions, the diode is in good condition and we have determined its polarity. If not, it is damaged.

  • If a LED is always on, it means that the semiconductor diode under test is shorted.
  • If no LED lights up, it means that the semiconductor diode under test is open.

This circuit is powered by a dual polarity power supply. You can also power up the circuit with two 9V batteries as shown in the circuit diagram. Resistor R4 is included in series with LEDs to limit the current passing through them.

Semiconductor diode tester components list

  • 1 741 Operational amplifier (IC1)
  • 2 1M resistors (R2, R3)
  • 1 6.8K resistor (R1)
  • 1 470 ohm resistor (R4)
  • 1 100 uF capacitor (C1)
  • 1 red LED (D2)
  • 1 green LED (D3)
  • 2 9V batteries (B1, B2)
  • 1 switch
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