How to determine Polarity of transistors in a circuit?

In summary: Polarity is determined by solving the circuit equation for the voltage drops across the components. If you get a positive answer, then you know that you guessed the correct polarity when you set up the problem. If you get a negative answer, then you know that you guessed the wrong polarity.
  • #1
Hamid1
17
0
Hi all,
In following image thare are Positive(+) and Negative(-) signs on above and under VEB and VCB
What's meaning of these signs?are they polarity of transistor?
why beside connection to ground is a negative sign?
15rkzn8.jpg

thanks in advance.
 
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  • #2
Those signs simply define the polarity of their respective voltages. This is similar to the current arrows which define the current direction.

When analyzing a circuit it is good to clearly label/define all current directions and voltage polarities.

There exists an unofficial notation convention (or notational aid) in which a label Vab is implied to mean Va-Vb, where Va and Vb are the voltages with respect to ground, on each side. This example seems to use that notation.
 
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  • #3
Thank you stevenb.
Can you explain how do I determine which one is Positive and which on is Negative?
 
  • #4
Hamid1 said:
Thank you stevenb.
Can you explain how do I determine which one is Positive and which on is Negative?

I'm not sure I understand your question. Do you mean, how do you determine which case has VEB or VCB postitive and which negative?

If so, then you simply solve the circuit equations and calculate the values of the voltage drops. If you get a positive answer, then you know that you guessed the correct polarity when you set up the problem. If you get a negative answer, then you know that you guessed the wrong polarity. Note, that I'm using the word "wrong" loosly here, since there is no right and wrong with a convention.

In the case of the NPN transistor, it's clear that VEB is negative and VCB is positive. You can see this just by looking at the battery polarity which is biasing the transistors. You can also see that the current directions are defined correctly (using the positive current convention with positive charge flow representing positive current).
 
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  • #5
Thanks.
That's exactly what I asked.
 

1. How do I identify the polarity of a transistor in a circuit?

To determine the polarity of a transistor in a circuit, you need to look at the transistor's pin configuration. The transistor will have three pins - base, emitter, and collector. The base pin is always located in the center, while the emitter and collector pins are located on either side. The polarity of the transistor can be identified by the location of the emitter and collector pins in relation to the base pin.

2. What are the different types of transistors and how do their polarities differ?

There are two main types of transistors - NPN and PNP. NPN transistors have a negative (N) type material sandwiched between two positive (P) type materials. This results in a negative base and a positive emitter and collector. On the other hand, PNP transistors have a positive (P) type material sandwiched between two negative (N) type materials, resulting in a positive base and a negative emitter and collector.

3. Can I determine the polarity of a transistor using a multimeter?

Yes, you can determine the polarity of a transistor using a multimeter in diode mode. Simply place the positive probe on the base pin and the negative probe on the emitter pin. If the multimeter reads a voltage drop, then the transistor is an NPN type. If there is no voltage drop, then it is a PNP type. You can also reverse the probes and check the voltage drop between the base and collector pins to confirm the polarity.

4. How do I know which pin is the base, emitter, and collector on a transistor?

The base pin is always located in the center of the transistor. The emitter and collector pins are located on either side of the base pin. However, the exact placement of these pins may vary depending on the type and manufacturer of the transistor. It is always best to refer to the datasheet or use a multimeter to determine the correct pin configuration for a specific transistor.

5. Is the polarity of a transistor important in a circuit?

Yes, the polarity of a transistor is crucial in a circuit as it determines the direction of current flow and affects the overall performance of the circuit. Using the wrong polarity transistor can result in the circuit not functioning properly or even damage the components. It is important to correctly identify and use the appropriate polarity transistor in a circuit.

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