Test: Limits of Operation - Electronics and Communication Engineering (ECE) MCQ

Power Dissipation in a BJT is given by P=V_CE.I_C. This is in the form of k=xy which is the equation of a hyperbola.

The region below I_C = I_CEO is called the cutoff region.

The region below V_CE < V_CEsat is called the saturation region.

Gain in dB = 10 log (4000).

 P=V_CE.I_C => 300mW = (12V)I_C => I_C=300/12 mA = 25 mA.

 P=V_CE.I_C => 300mW = V_CE(50 mA) => V_CE = 300/50 = 6 V.

From the curve, we get change in I_C = (8.2-6.4) mA and change in I_B = 10 uA. Hence, /beta; = (1.8/0.01) = 180.

If the positive lead of a DMM, with the mode set to ohmmeter is connected to the base and the negative lead to the emitter and a low resistance reading is obtained, then what is the type of transistor that is being tested is npn.

When testing a transistor using a Digital Multimeter (DMM) set to the ohmmeter (resistance) mode, the readings can help identify the type of transistor based on the behavior of its internal junctions. Let's analyze the scenario step-by-step.

Given Scenario:

• Connections:
  • Positive Lead (Red) of the DMM is connected to the Base.
  • Negative Lead (Black) of the DMM is connected to the Emitter.
• Observation: A high resistance reading is obtained.

Understanding Transistor Types:

Transistors primarily come in two types:

1. NPN Transistor
2. PNP Transistor

Each type has different configurations of p-type and n-type semiconductor materials:

• NPN Transistor:
  • Structure: Emitter (n-type) → Base (p-type) → Collector (n-type)
  • Base-Emitter Junction: p-n junction
• PNP Transistor:
  • Structure: Emitter (p-type) → Base (n-type) → Collector (p-type)
  • Base-Emitter Junction: n-p junction

Behavior During Testing:

1. Testing an NPN Transistor:

   • Connection: Positive (Red) to Base (p-type), Negative (Black) to Emitter (n-type)
   • Result: This forward biases the base-emitter junction (like a forward-biased diode), allowing current to flow.
   • DMM Reading: Low resistance

2. Testing a PNP Transistor:

   • Connection: Positive (Red) to Base (n-type), Negative (Black) to Emitter (p-type)
   • Result: This reverse biases the base-emitter junction (like a reverse-biased diode), preventing current flow.
   • DMM Reading: High resistance

Applying to the Given Scenario:

• Observation: High resistance is obtained when the positive lead is connected to the base and the negative lead to the emitter.
• Inference: Since a high resistance reading indicates that the base-emitter junction is reverse biased, it aligns with the behavior of a PNP transistor under these connections.

Conclusion:

Based on the high resistance reading when the positive lead is connected to the base and the negative lead to the emitter, the transistor being tested is a PNP transistor.

Answer:
a) pnp

 With the curved side facing away the correct lead sequence is base, collector, emitter.