Question

A boy designs a circuit to study the input and output characteristics of an npn transistor

1. Identify the transistor configuration, input current and output current 

2. By keeping the output voltage constant, the boy measures the input current by varying the input voltage. If a graph is drawn, what is the nature of the input characteristic? Justify your answer.

Answer 1

1. Common Emitter, i_b and i_c 

2. Input Characteristics (CE configuration):

The graph connecting base current with base emitter voltage (at constant VCE) is the input characteristics of the transistor.

To study the input characteristics, the collector to emitter voltage (V_CE) is kept at constant. The base current I_B against V_BE is plotted in a graph. The ratio ∆V_BE /∆_IB at constant V_CE is called the input resistance. i.e.,Input resistance = r_i = \(\frac{ΔV_{BE}}{ΔI_B}\)