## Sunday, September 10, 2023

Today I am going to make a circuit of continuity tester.Using this circuit we can test continuity of many components like as Diode, LED etc.This circuit I will make using BC547 transistor.

How to Find the Base, Collector, Emitter, Direction & Condition of Transistor by Multimeter

How to remember the direction of PNP and NPN Transistor & Pin Identification, Check if it is Good or Bad.

The following basic tutorial based on using digital (DMM) or analog (AVO) multimeter will help you to:

Remember the direction of NPN and PNP Transistors

Identify the Base, Collector & Emitter of a Transistor

Check a transistor if it is Good or Bad.

Test a Transistor using Digital Multimeter in Diode or Continuity Mode

To do so, follow the instructions given below.

Remove the transistor from the circuit i.e. disconnect the power supply across the transistor which has to be tested. Discharge all the capacitors (by shorting the capacitor leads) in the circuit (If any).

Set the meter to “Diode Test” Mode by turning the rotary switch of the multimeter.

Connect the Black (common or -Ve) test lead of the multimeter to the 1st terminal of the transistor and Red (+Ve) test lead to the 2nd terminal (Fig below). You have to perform 6 tests by connecting the Black (-Ve) test lead and Red (+Ve) test lead to 1 to 2, 1 to 3, 2 to 1, 2 to 3, 3 to 1, 3 to 2 respectively by just replacing the multimeter test leads or reverse the transistor terminals to connect, test, measure and note the reading in the table (shown below). Numbers in Red colors are Red Test Lead and numbers in Black are connected to Black (-Ve) test lead of multimeter.

Test, measure and note the display reading shown in the multimeter in the table below.

We have the following data from the table given below.

Out of 6 tests, we got data and results only on two tests i.e. points 2 to 1 and 2 to 3. Where we got at points 2 to 1 is 0.733 VDC and 2 to 3 is 0.728 VDC. Now, we can easily find the type of transistor as well as their collector, base and emitter.

Point 2 is Transistor Base in BC55 Transistor.

BC 557 is a PNP Transistor where the 2nd (middle terminal is base) connected to Red (+Ve) test lead of the multimeter.

At all, Terminal 1 = Emitter, Terminal 2 = Base, and Terminal 3 = Collector (BC 557 PNP Transistor) because, the test result for 2-1 = 0.733 VDC and 2-3 = 0.728 VDC, i.e. 2-1 > 2-3.

2nd Method using DMM to find the Base of the Transistor.

If you follow the same pattern and connecting method of multimeter leads and transistor terminals one by one in the figure shown above, in fig “c” and “d”, The Red (+Ve) test lead is connected to the middle one i.e. 2nd terminal of lead and the Black (-Ve) test lead is connected to the 1st one terminal of transistor.

Again, The Red (+Ve) test lead is connected to the middle one i.e. 2nd terminal of lead and the Black (-Ve) test lead is connected to the 3rd one terminal of transistor and multimeter shows some reading i.e. 0.717 VDC & 0.711 VDC respectively in the case of BC 547 NPN.

The common lead is 2nd one connected to Red (+Ve) test lead (i.e. P and yes, the other two leads are N) which is base. The case is reversed in the case of the BC 557 PNP transistor.

NPN or PNP?

It's simple. If the Black (-Ve) test lead of the multimeter is connected to the base of the transistor (2nd terminal in our case), then it is PNP transistor, and when Red (+Ve) test lead is connected to the base of the terminal, It is NPN transistor.

Check a Transistor using Analog or Digital Multimeter in Ohm (Î©) Range Mode:

Disconnect the power supply to the circuit and remove the transistor from the circuit.

Rotate the selector switch and put the Multimeter knob in Ohm Range (OHM)

Connect the Black (common or -Ve) test lead of the multimeter to the 1st terminal of the transistor and Red (+Ve) test lead to the 2nd terminal (Figure 1 (a). (You have to perform 6 tests by connecting the Black (-Ve) test lead to 1 to 2, 1 to 3, 2 to 1, 2 to 3, 3 to 1, 3 to 2 respectively by just replacing the multimeter test leads or reverse the transistor terminals to connect, test, measure and note the reading in the table (shown below). (Numbers in Red colors show the transistor leads connected to the Red (+Ve) test lead of multimeter and the numbers in black colors show the transistor leads connected to the Black (-Ve) ) test lead of multimeter. (Better explanation in the table & fig below)

If the multimeter shows high resistance in both first and second tests by changing the polarity of either transistor or multimeter, as shown in Fig 1 (a) and (b). (Note that, the result will be shown only for 2 tests out of 6 as mentioned above). i.e. In our case, the 2nd terminal of the transistor is BASE, because it shows high resistance in both tests of 2 to 3 and 3 to 2 where Red (+Ve) test lead of the multimeter is connected to the 2nd terminal of the transistor. In other words, the common number in tests is Base which is 2 out of 1, 2 and 3.

PNP or NPN ?

Now, it is a NPN transistor because, it shows reading only when the RED (+Ve) test lead (i.e.P terminal where P = Positive) is connected to the Base of the transistor (See fig below). If you do the reverse, i.e. Black (-Ve) test lead (i.e. N = where N = Negative) of multimeter connected to the transistor terminal in sequence of (1 to 2 and 2 to 3) and shows reading in both tests as above, The 2nd Terminal is still BASE , but the transistor is PNP ( see fig below).

Testing a Transistor using a Digital Multimeter in the Transistor or hFE or Beta Mode

hFE also known as beta is dc gain stands for “Hybrid parameter forward current gain, common emitter” used to measure the hFE of a transistor which can be found by the following formula.

Today I am going to make a circuit of continuity tester.Using this circuit we can test continuity of many components like as Diode, LED etc.This circuit I will make using BC547 transistor.

How to Find the Base, Collector, Emitter, Direction & Condition of Transistor by Multimeter

How to remember the direction of PNP and NPN Transistor & Pin Identification, Check if it is Good or Bad.

The following basic tutorial based on using digital (DMM) or analog (AVO) multimeter will help you to:

Remember the direction of NPN and PNP Transistors

Identify the Base, Collector & Emitter of a Transistor

Check a transistor if it is Good or Bad.

Test a Transistor using Digital Multimeter in Diode or Continuity Mode

To do so, follow the instructions given below.

Remove the transistor from the circuit i.e. disconnect the power supply across the transistor which has to be tested. Discharge all the capacitors (by shorting the capacitor leads) in the circuit (If any).

Set the meter to “Diode Test” Mode by turning the rotary switch of the multimeter.

Connect the Black (common or -Ve) test lead of the multimeter to the 1st terminal of the transistor and Red (+Ve) test lead to the 2nd terminal (Fig below). You have to perform 6 tests by connecting the Black (-Ve) test lead and Red (+Ve) test lead to 1 to 2, 1 to 3, 2 to 1, 2 to 3, 3 to 1, 3 to 2 respectively by just replacing the multimeter test leads or reverse the transistor terminals to connect, test, measure and note the reading in the table (shown below). Numbers in Red colors are Red Test Lead and numbers in Black are connected to Black (-Ve) test lead of multimeter.

Test, measure and note the display reading shown in the multimeter in the table below.

We have the following data from the table given below.

Out of 6 tests, we got data and results only on two tests i.e. points 2 to 1 and 2 to 3. Where we got at points 2 to 1 is 0.733 VDC and 2 to 3 is 0.728 VDC. Now, we can easily find the type of transistor as well as their collector, base and emitter.

Point 2 is Transistor Base in BC55 Transistor.

BC 557 is a PNP Transistor where the 2nd (middle terminal is base) connected to Red (+Ve) test lead of the multimeter.

At all, Terminal 1 = Emitter, Terminal 2 = Base, and Terminal 3 = Collector (BC 557 PNP Transistor) because, the test result for 2-1 = 0.733 VDC and 2-3 = 0.728 VDC, i.e. 2-1 > 2-3.

2nd Method using DMM to find the Base of the Transistor.

If you follow the same pattern and connecting method of multimeter leads and transistor terminals one by one in the figure shown above, in fig “c” and “d”, The Red (+Ve) test lead is connected to the middle one i.e. 2nd terminal of lead and the Black (-Ve) test lead is connected to the 1st one terminal of transistor.

Again, The Red (+Ve) test lead is connected to the middle one i.e. 2nd terminal of lead and the Black (-Ve) test lead is connected to the 3rd one terminal of transistor and multimeter shows some reading i.e. 0.717 VDC & 0.711 VDC respectively in the case of BC 547 NPN.

The common lead is 2nd one connected to Red (+Ve) test lead (i.e. P and yes, the other two leads are N) which is base. The case is reversed in the case of the BC 557 PNP transistor.

NPN or PNP?

It's simple. If the Black (-Ve) test lead of the multimeter is connected to the base of the transistor (2nd terminal in our case), then it is PNP transistor, and when Red (+Ve) test lead is connected to the base of the terminal, It is NPN transistor.

Check a Transistor using Analog or Digital Multimeter in Ohm (Î©) Range Mode:

Disconnect the power supply to the circuit and remove the transistor from the circuit.

Rotate the selector switch and put the Multimeter knob in Ohm Range (OHM)

Connect the Black (common or -Ve) test lead of the multimeter to the 1st terminal of the transistor and Red (+Ve) test lead to the 2nd terminal (Figure 1 (a). (You have to perform 6 tests by connecting the Black (-Ve) test lead to 1 to 2, 1 to 3, 2 to 1, 2 to 3, 3 to 1, 3 to 2 respectively by just replacing the multimeter test leads or reverse the transistor terminals to connect, test, measure and note the reading in the table (shown below). (Numbers in Red colors show the transistor leads connected to the Red (+Ve) test lead of multimeter and the numbers in black colors show the transistor leads connected to the Black (-Ve) ) test lead of multimeter. (Better explanation in the table & fig below)

If the multimeter shows high resistance in both first and second tests by changing the polarity of either transistor or multimeter, as shown in Fig 1 (a) and (b). (Note that, the result will be shown only for 2 tests out of 6 as mentioned above). i.e. In our case, the 2nd terminal of the transistor is BASE, because it shows high resistance in both tests of 2 to 3 and 3 to 2 where Red (+Ve) test lead of the multimeter is connected to the 2nd terminal of the transistor. In other words, the common number in tests is Base which is 2 out of 1, 2 and 3.

PNP or NPN ?

Now, it is a NPN transistor because, it shows reading only when the RED (+Ve) test lead (i.e.P terminal where P = Positive) is connected to the Base of the transistor (See fig below). If you do the reverse, i.e. Black (-Ve) test lead (i.e. N = where N = Negative) of multimeter connected to the transistor terminal in sequence of (1 to 2 and 2 to 3) and shows reading in both tests as above, The 2nd Terminal is still BASE , but the transistor is PNP ( see fig below).

Testing a Transistor using a Digital Multimeter in the Transistor or hFE or Beta Mode

hFE also known as beta is dc gain stands for “Hybrid parameter forward current gain, common emitter” used to measure the hFE of a transistor which can be found by the following formula.