How can one tell if the NPN transistor is damaged?

Question

I am using a 2n3055 NPN transistor as a switch gate. The base is supplied via a signal gnerator. One moment, it was working fine and then... all went silent. How can I tell if it is the fault of the transistor?

Answer 1

In my experience it is usually the base emitter junction that fails. This can be easily measured with an ohm meter out of the circuit. You should see (using the diode test mode on the multimeter) very low ohms in one direction and very high in the other.

In situ, with the voltage on, if you measure more than .7V on the base, with respect to emitter, the device is blown!

Note. You have to use the "diode test" function of the multimeter because it puts the 9V battery into play giving enough voltage to turn on the base-emitter diode junction. If you don't you cannot see the forward biased junction.

Answer 2

Testing a transistor Transistors can be damaged by heat when soldering or by misuse in a circuit. If you suspect that a transistor may be damaged there are two easy ways to test it: testing a transistor Testing an NPN transistor 1. Testing with a multimeter Use a multimeter or a simple tester (battery, resistor and LED) to check each pair of leads for conduction. Set a digital multimeter to diode test and an analogue multimeter to a low resistance range. Test each pair of leads both ways (six tests in total): * The base-emitter (BE) junction should behave like a diode and conduct one way only. * The base-collector (BC) junction should behave like a diode and conduct one way only. * The collector-emitter (CE) should not conduct either way. The diagram shows how the junctions behave in an NPN transistor. The diodes are reversed in a PNP transistor but the same test procedure can be used. testing a transistor A simple switching circuit to test an NPN transistor 2. Testing in a simple switching circuit Connect the transistor into the circuit shown on the right which uses the transistor as a switch. The supply voltage is not critical, anything between 5 and 12V is suitable. This circuit can be quickly built on breadboard for example. Take care to include the 10kohm resistor in the base connection or you will destroy the transistor as you test it! If the transistor is OK the LED should light when the switch is pressed and not light when the switch is released. To test a PNP transistor use the same circuit but reverse the LED and the supply voltage.

Answer 3

How To Check A Transistor

Answer 4

How To Test A Transistor

Answer 5

You can use a regular ohmmeter to check if a transistor is blown. Connect the common probe to the base; the other probe connect to the collector. You will either get a very high (open circuit) reading or a low reading (depending on whether the common probe is + or - with respect to the measuring probe). Then move the the measuring probe to the emitter; it should read the same as the collector. Then reverse the leads; if both reading were high before, the should both be low now, and vice versa. (If your meter has a diode test function, use that, otherwise set the meter on a high resistance range like 10Kohm).

If you get low readings in both directions from either base-collector or base-emitter, the transistor is shorted on one junction. If you get open readings in both directions, the junction is open.

Answer 6

being that you are using 2N3055 as a switch gate, one way to test, is to hardwire a bias voltage to the base of the transistor, if it switches on(the load you are driving), the transistor is still working, else it doesn't.

normally setting the multimeter to diode testing, and putting the +probe to the base and -probe to the emitter will turn on the transistor also.

2n3055 is a power transistor but it doesn't have a build in fly-back diode. so if it is used as a gate for inductive load, a fly-back diode is required, else when the transistor goes from on to off, the voltage build up by the inductive load will kill the transistor

Answer 7

The quickest way is to measure the forward and reverse conduction of the emitter and collector junctions. If either of them is shorted or open, the transistor is dead.
And, if it dead, it might be a good idea to find out -why- it died before you put another transistor in the circuit and kill it ☺

Doug