This article discusses various circuits that can be used to test a Transistor, both NPN and PNP. We have structured this article into two circuits. If you have any doubts about any section please ask through comments.
1. Transistor Tester built using Transistors
Persamaan transistor pnp dan npn - 28 images - kursus elektro surabaya sidoarjo mengenal komponen elektronika dan pengujiannya, electrooper perbedaan transistor npn. Kedalam dua jenis yaitu transistor PNP dan transistor. (Ic), dan semakin besar. Arus pada transistor dan di simbol-kan sebagai hFE, persamaan hFE adalah.
2. Simple Transistor Tester (Contains both Circuit Diagram and PCB Lay Out)
3. LED Based Transistor Test
1. Transistor Test Circuit
Description.
Here is a very simple circuit that can be used to check the hfe of transistors. Both PNP and NPN transistors can be checked using this circuit. Hfe as high as 1000 can be measured by using this circuit.The circuit is based on two constant current sources build around transistors Q1 and Q2.The Q1 is a PNP transistor and the constant current flows in the emitter lead. The value of constant current can be given by the equation; (V D1 -0.6)/ (R2+R4).The POT R4 can be adjusted to get a constant current of 10uA.
The Q2 is an NPN transistor and the constant current flows into the collector lead. The value of this constant current can be given by the equation; (VD2-0.6)/(R3+R5).The POT R5 can be adjusted to get a constant current of 10uA.This constant current provided by the Q1 circuit if the transistor under test is an NPN transistor and by Q2 circuit if the transistor under test is a PNP transistor is fed to the base of transistor under test. This current multiplied by the hfe flows in the collector of the transistor and it will be indicated by the meter. The meter can be directly calibrated to read the hfe of the transistor.
Circuit diagram with Parts list.
Notes.
- Assemble the circuit on a general purpose PCB.
- The circuit can be powered from a general purpose PCB.
- J1 and J2 are transistor sockets.
- The Zener diodes must be rated at least 400mW.
2. Simple Transistor Tester
Note: This circuit is developed by our Author: Vysakh
Simple transistor tester is a transistor analyzer circuit which is suitable for testing both NPN and PNP transistors. This is a very simple circuit as compared to other transistor testers. This circuit is very useful for both technicians and students. This circuit can be easily assembled on a general purpose PCB. A basic electronic component like resistors, LED’s, diode and transformer is used for developing this circuit. Using this circuit, we can check whether a transistor is in good condition or not, is it opened or shorted, and so on.
Working
The principle behind this circuit is very simple. This circuit basically works on the basis of transistor switching action (Basic Transistor Theory). Take a look at the circuit diagram given below.
Testing of NPN Transistor
- Let us start by connecting an NPN transistor to the circuit with the corresponding Emitter, Base, and Collector terminals and the switch on the circuit.
- During the first half cycle of the transformer input , the emitter base junction of transistor is forward biased and collector base junction is reverse biased and the transistor is in ON state and diode D1 is in forward biased The current starts flow through the D1 and the red LED begins to glow. During the next half cycle, the transistor is reverse biased and is in OFF state.
- By the alternative nature of the input AC , we can see that the red LED is in ON state and the transistor is in good working condition(Diode D2 and Green Led is in reverse biased and in OFF state). By using the variable resistor, we can check the transistor with various base currents.
- If the NPN transistor is in open state, the transistor does not conduct and no current flow through LED. If the transistor is in shorted condition, the transistor acts as a closed switch. And both diode conduct alternatively and both LED’s starts glowing.
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Testing of PNP transistor
The PNP transistor is attached to the device with corresponding pin terminals and switch on the circuit. If, during one half cycle of the input AC (assume top terminal of transformer is negative and bottom is positive), the emitter base and collector base junctions of the transistor are forward biased. Then, in such a condition if there is a and a current flow through the Diode D2 and the Green LED starts glowing, then understand that the transistor is in good working condition(the Diode D1 and Red LED is in reverse biased and not working at that time). During the next half cycle both diodes, and transistors are reverse biased and in OFF state. By the alternating property of input AC, we feel the Green LED is in ON state. We can check this circuit by providing various base currents (by very the variable resistor.
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If the PNP transistor is in open state, it doesn’t conduct in both half cycles and no output is obtained. If the transistor is in a shorted condition, transistor acts as a closed path and both diodes are forward biased alternatively, thus making the two LED’s glow at the same time.
The PCB layout of Simple transistor tester also given below.
In electronics most commonly failed component is transistor. To test the working of the transistor, one must go through a lot of testing though multimeter. By testing one terminal after another, this consumes a lot of time and also this option is no good for newbies. The transistor testing circuits which are present already are complex to understand and design. In this tutorial we will design a simple 555 TIMER based circuit which will test the working of the transistor in seconds. This circuit is the convenient way to check the working of a transistor for newbies.
The easiest way to check a transistor's working is by testing its switching characteristics. So in this circuit we are going to make transistor switch an LED on and off continuously. The timer here generates clock of 1 Hz and is fed to transistor which is to be tested to drive an LED.
The 555 IC works in free running mode with an adjustable frequency option. With variable frequency one can double check the working of transistor.
Circuit Components
- +9V supply voltage
- 555 IC
- 1KΩ resistors (2 pieces), 2K2Ω resistors
- 10KΩ pot or variable resistor
- 100µF capacitor
- LED
- Transistor (that needed to be tested)
Circuit Diagram and Explanation
The figure shows the circuit diagram of TRANSISTOR TESTER. In this circuit the timer function is to work as a square wave generator and to provide clock for the transistor. This clock is connected to the transistor (transistor to be tested) base. The transistor is provided with a LED to drive. For testing the transistor, its terminals should be connected exactly as give in the table,
A | B | C | |
NPN | collector | base | emitter |
PNP | emitter | base | collector |
Once connected according to the table, power should be turned on and check the following conditions to get the conclusion on transistor working.
The conditions for Transistor working are:
- The LED should be blinking continuously.
- If the pot is adjusted, then LED should be blinking at a different frequency and so both should have relation.
The conditions for Transistor not working are:
- If the LED is off continuously.
- If the LED is on continuously (not blinking).
- Not showing frequency change with pot adjustment.
- Temperature of transistor rising.
The circuit above has current limiting resistors; by this the circuit we will have no problem bearing the short circuit current of a broken transistor. So the circuit can test any transistor without any problem.
The terminal connections should be paid attention during connection, as some transistors have protection diodes causing the LED to turn on continuously and it gives false conclusion.
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The capacitor in the circuit can be replaced with a 10uF one for higher frequency of blinking.
Working
Before understanding the working of this circuit, it should be know that a NPN transistor respond to positive voltage only, so to turn on an NPN transistor we should give a voltage greater than 1V. Once the positive voltage is provided at the base, the NPN transistor move from cutoff mode to saturation mode. As for a PNP, to turn on it should be provided with voltage less than or equal to zero. So if the base of a PNP is connected to ground it moves in to conduction.
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The clock provide by the timer have positive voltage for half cycle and ground for other half. So the NPN responds to the positive voltage cycle and the PNP responds to the 0V half cycle.
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With these triggers the transistor moves to conduction and drives the LED, so the Led blinks.