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Semiconductor Tester Schematic Circuit Diagram

Versatile Semiconductor Device Tester

Capable of testing a wide spectrum of semiconductor devices, from switching diodes to power transistors, the tester offers valuable utility. Additionally, it provides a basic indication of the gain of bipolar transistors and proves to be a helpful tool for identifying functional, short-circuited, and internally open devices within semiconductor batches.

Single CMOS IC-Based Tester with Visual Indication

The tester’s foundation lies in a single CMOS IC and a bi-color LED serving as a visual indicator. The RC oscillator formed by Gate IC1a is the core element. The oscillator signal is buffered and presented in both true and inverted forms by the three remaining gates in the IC. The bi-color LED, capable of displaying red or green, signals the direction of the current passing through the test probes or the device being tested. Resistor R1 plays a crucial role as a current limiter.

Semiconductor tester Schematic diagram

Semiconductor Device Test Points and Sockets

The input and output signals of gate IC1 are directed to a set of test probes. A two-terminal test socket designed for diodes, and a three-terminal transistor socket. The base current for the transistor under test (TUT) is adjustable through a preset. This preset can be calibrated using known, functional transistors to establish an approximate gain scale.

LED Indication for Functional Semiconductor Devices

When a semiconductor is operational, only one LED illuminates. The LED’s color serves as an indicator of the component’s polarity (n-p-n or p-n-p, or cathode/anode). If the component is internally open, none of the LEDs light up. A semiconductor with an internal short circuit is easily identifiable by both green and red LEDs lighting simultaneously with approximately equal intensity. Proper connection of transistors to the indicated socket terminals—base, collector, and emitter pins—is crucial. So pinout verification before conducting the test is recommended.

Circuit as a Continuity Tester and Current Characteristics

This circuit can function as a straightforward continuity tester. It draws a current of approximately 300 mA without a Diode Under Test (DUT) or Transistor Under Test (TUT) connected, and about 7.5 mA when the probes are short-circuited.

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