While diagnosing an NPN BJT in a SOT-23 package, your multimeter positive probe (+) is locked on the Base (Pin 1). Measuring to Pin 3 reads 0.6 V, while measuring to Pin 2 reads 0.68 V. Which pin is the Emitter?
Pin 2 is the Emitter, because it has the higher voltage drop.
To determine which pin is the Emitter in the given NPN BJT in a SOT-23 package, we need to understand the behavior of a bipolar junction transistor (BJT) and the typical voltage drops across its junctions when measured with a multimeter.
- When diagnosing a BJT, a common approach is to use the diode test function of a multimeter. In this mode, the multimeter measures the forward voltage drop across a semiconductor junction.
- For an NPN transistor, the Base-Emitter (BE) junction acts like a diode with its anode at the base, and the Base-Collector (BC) junction also acts like a diode but typically with a higher voltage drop when measured in this manner.
- In this scenario, the multimeter's positive probe (+) is connected to the Base (Pin 1), and two voltage drops are measured:
- 0.6 V when measuring between Base (Pin 1) and Pin 3.
- 0.68 V when measuring between Base (Pin 1) and Pin 2.
- Since the Base-Emitter junction has a characteristic forward voltage drop of around 0.6 - 0.7 V, and given that a higher drop typically indicates the Base-Emitter junction rather than the Base-Collector junction, Pin 2, which shows a higher voltage drop of 0.68 V, is determined to be the Emitter.
Based on the behavior of BJTs and the observed voltage measurements, the correct answer is that Pin 2 is the Emitter because it has the higher voltage drop.
By elimination:
- Neither pin; the transistor is broken because the readings don't match: This is incorrect as the readings are consistent with a typical NPN transistor.
- Both pins are identical and can be used interchangeably: This is incorrect because BJTs have distinct Collector, Base, and Emitter pins with different roles and characteristics.
- Pin 3 is the Emitter, because it has the lower voltage drop: This is incorrect because the lower voltage drop suggests a Base-Collector junction rather than a Base-Emitter junction.
Thus, the conclusion is that Pin 2 is the Emitter because it has the higher voltage drop. This conclusion is consistent with the typical behavior of an NPN transistor's Base-Emitter junction.
Similar Questions
Which set of terminals is commonly used to connect a Field Effect Transistor in a circuit?
In an n-channel enhancement mode MOSFET, what must be applied to the gate terminal relative to the source to turn the device on?
What is the configuration called when the emitter terminal of a transistor is common to both input and output circuits?
How does the construction of a MOSFET help to achieve high input impedance?
Which type of charge carriers mainly control current in a Field Effect Transistor (FET)?
Why are transistors preferred over mechanical switches for rapid switching operations?
What is the purpose of the base region in an NPN transistor?
In the output characteristics of a common-emitter configuration, a family of curves is obtained by varying VCE while keeping which quantity fixed? (Symbols have their usual meaning.)
The common-emitter (CE) configuration of a transistor is most widely used as a/an:
Important Questions from Transistors
Heat sink of a power transistor can be used for:
Transistors used as power amplifiers are generally mounted on a metallic plate so as to-
MOSFET can be used as a
In a C-E configuration, an emitter resistor is used for:
Which of the following transistor amplifier configuration is used as a buffer for impedance matching.
