- #1
Bassalisk
- 947
- 2
Hello,
I just bought lot of pnp and npn transistors. They are not labeled. How do i tell them apart?!
I just bought lot of pnp and npn transistors. They are not labeled. How do i tell them apart?!
Studiot said:
Averagesupernova said:Sure you can use an ohmeter to check the base emitter junction. Now tell me how you will tell it from the base collector junction. This method will tell you the difference between NPN and PNP but it won't likely tell you which is the collector and which is the emitter.
Studiot said:
I like the find by Studiot:
Pretty straightforward.
Studiot said:But it is not always that straightforward and an electonics/electrical major should known the pitfalls.
Yes, I seem to remember you have recently bought or borrowed a digital multimeter.
Older type Analog meters, with pointers respond to current not voltage.
We make a voltmeter out of them by putting a high value resistor in series with them.
We make an ohmmeter by putting a ressitor either in series or paralle with the unknown and measuring the current through the resistor. This yields in a highly non linear scale.
In order to measure higher value resistors we need a relatively high supply voltage (my old meter had 22.5 volts.)
This high voltage was more than enough to turn on (bias on in the forward direction or sometimes breakdown in the reverse) semiconductor junctions.
Further the colours of the terminals and leads of these older type meters were reversed ie the black lead produced a positive voltage on the black lead.
So you cannot use this type of meter to measure in resistors incircuit as you will switch or destroy junctions. Electronic ohmeters were introduced that applied about 0,2 volts to overcome this.
Modern digital meters respond to voltage
So we make current meters by measuring the voltage across a known resistor with them.
We measure resistance by either passing a constant current through the resistor and measuring the voltage or using a feedback amplifier or by other means.
Whichever we do, the red lead should now be positive and around 0.2 volts only applied to the unknown resistor.
This means that we can no longer use an ohmmeter to test for forward and reverse resistance on a junction as we simply will not switch it on.
So modern meters have a special setting which applies sufficient current limited voltage to turn on the junction and presents the voltage across it as a reading in the forward direction.
But I have special feature on my multimeter, called diode test, designed specially for diodes. I don't think it sends large currents through test leads because its designed for diodes.
They should come up with something like marking to clearly distinguish npn and pnp transistors.Studiot said:The test polarity is important if you have an unmarked diode (or transistor) and you want to use your diode test to determine which is the anode and which is the cathode
One way to identify the type of transistor is by looking at the symbol printed on it. NPN transistors have an arrow pointing outwards from the base terminal, while PNP transistors have an arrow pointing inwards towards the base terminal.
Yes, you can use a multimeter to identify the type of transistor. Set the multimeter to the diode test mode and place the probes on the base and emitter terminals. If the multimeter reads a forward voltage drop, then it is an NPN transistor. If it reads a reverse voltage drop, then it is a PNP transistor.
PNP and NPN transistors have opposite polarity, which means the direction of current flow is reversed. In an NPN transistor, the current flows from the collector to the emitter, while in a PNP transistor, the current flows from the emitter to the collector. Additionally, the biasing and voltage requirements for these two types of transistors are also different.
The pinout of a transistor can be determined by identifying the base, emitter, and collector terminals. The base terminal is typically the middle leg, while the emitter and collector terminals are on either side. You can also use a datasheet or a transistor tester to determine the pinout.
Yes, it is crucial to identify the type of transistor before using it in a circuit. Using the wrong type of transistor can result in circuit failure or damage to the transistor. It is also essential to understand the polarity and voltage requirements of the transistor to ensure proper circuit operation.