29-08-2017, 11:38 AM
This tester is primarily intended to test bipolar transistors. It can indicate the transistor type as well as identify its base, collector and emitter pins. The circuit is very simple. The direction of current flow from the terminals of the transistor under test (TUT) is indicated by a pair of LEDs (green-red). An npn transistor produces a red-green-red glow, while a pnp transistor produces a green-red-green glow, depending on the test point that connects to the transistor terminal. The transmitter and the collector are differentiated by pressing the pushbutton S1 which actually increases the supply voltage of the circuit by about 5.1 V.
At the heart of the circuit is IC CD4069 (IC3), which oscillates and produces pulses needed to test a pair of transistor conductors for conduction in both directions. Different combinations are selected by an arrangement of the counter CD4040 (IC1) and the bilateral switch CD4016 (IC2).
Figure 1 shows the circuit of the bipolar transistor tester. A pair of LEDs is connected to each test point through which current flows in both directions. Each LED corresponds to a particular address. In this way, both junctions of the transistor can be tested. The LEDs are arranged to indicate the type of semiconductor through the junction p-n. The counter is synchronized by the AC generator built around the gates N5 and N6. This causes the LEDs to glow continuously to facilitate observation, revealing the direction of current flow between the different test points. So if the red LED connected to a certain point shines, it means that the type n of the junction is connected to that test point, and vice versa. Thus, a red-green-red glow indicates the npn type of the transistor, while a green-red-green glow indicates a pnp transistor. From this observation, you can easily detect the base.
The manifold and the emitter differ based on the principle that the base-emitter junction is broken under reverse polarization much more easily than the base-collector junction. Thus, under an increased AC voltage, it is easy to see that the transmitter conducts more in the reverse direction (the associated LED shines significantly) than the manifold. The use of transparent or semitransparent LEDs is recommended.
Set the VR1 preset (2 mega ohms) to get the same brightness when there are two test points in short circuit. Unregulated 15V-18V is regulated by the zener-transistor combination to power the circuit.
The test procedure is simple. Typically, transistors can be plugged into any orientation as they come in a variety of possible base arrangements, manifold and emitters, such as CEB, BEC and CBE. Simply connect the TUT to the possible combinations of three points. A red-green-red glow means it is an npn transistor and the pin associated with the green LED is the base. To identify the emitter and manifold, simply press switch S1 and observe the green LEDs adjacent to the already bright red LEDs. The glowing green LED with a high current indicates the side of the emitter, while the low intensity LED indicates the collector side.
Similarly, a green-red-green glow means that the transistor is pnp-type and the pin associated with the red LED is the base. To identify the emitter and collector, simply press switch S1 and observe the red LEDs associated with bright green LEDs on the sides. The glowing LED with a high current indicates the side of the emitter, while the low intensity LED indicates the side of the collector.
Mount the circuit on a general purpose PCB and enclose it in a small box. Keep the preset knob in the middle. In order to be easy to connect the TUT, you can increase the number of test points as shown in the prototype of the author in Fig. 2.
At the heart of the circuit is IC CD4069 (IC3), which oscillates and produces pulses needed to test a pair of transistor conductors for conduction in both directions. Different combinations are selected by an arrangement of the counter CD4040 (IC1) and the bilateral switch CD4016 (IC2).
Figure 1 shows the circuit of the bipolar transistor tester. A pair of LEDs is connected to each test point through which current flows in both directions. Each LED corresponds to a particular address. In this way, both junctions of the transistor can be tested. The LEDs are arranged to indicate the type of semiconductor through the junction p-n. The counter is synchronized by the AC generator built around the gates N5 and N6. This causes the LEDs to glow continuously to facilitate observation, revealing the direction of current flow between the different test points. So if the red LED connected to a certain point shines, it means that the type n of the junction is connected to that test point, and vice versa. Thus, a red-green-red glow indicates the npn type of the transistor, while a green-red-green glow indicates a pnp transistor. From this observation, you can easily detect the base.
The manifold and the emitter differ based on the principle that the base-emitter junction is broken under reverse polarization much more easily than the base-collector junction. Thus, under an increased AC voltage, it is easy to see that the transmitter conducts more in the reverse direction (the associated LED shines significantly) than the manifold. The use of transparent or semitransparent LEDs is recommended.
Set the VR1 preset (2 mega ohms) to get the same brightness when there are two test points in short circuit. Unregulated 15V-18V is regulated by the zener-transistor combination to power the circuit.
The test procedure is simple. Typically, transistors can be plugged into any orientation as they come in a variety of possible base arrangements, manifold and emitters, such as CEB, BEC and CBE. Simply connect the TUT to the possible combinations of three points. A red-green-red glow means it is an npn transistor and the pin associated with the green LED is the base. To identify the emitter and manifold, simply press switch S1 and observe the green LEDs adjacent to the already bright red LEDs. The glowing green LED with a high current indicates the side of the emitter, while the low intensity LED indicates the collector side.
Similarly, a green-red-green glow means that the transistor is pnp-type and the pin associated with the red LED is the base. To identify the emitter and collector, simply press switch S1 and observe the red LEDs associated with bright green LEDs on the sides. The glowing LED with a high current indicates the side of the emitter, while the low intensity LED indicates the side of the collector.
Mount the circuit on a general purpose PCB and enclose it in a small box. Keep the preset knob in the middle. In order to be easy to connect the TUT, you can increase the number of test points as shown in the prototype of the author in Fig. 2.