Test: The CE Characteristics & CB Characteristics - Electrical Engineering (EE) MCQ

A graph of I_B against V_BE is drawn. The curve so obtained is known as input characteristics. The collector emitter voltage (V_CE) is kept constant.

The ratio of change in base emitter voltage (∆V_BE) to resulting change in base current (∆I_B) at constant collector emitter voltage (V_CE) is defined as input resistance. This is denoted by r_i.

 A graph of I_C against V_CE is drawn. The curve so obtained is known as output characteristics. The base current (I_B) is kept constant.

The ratio of change in collector emitter voltage (∆V_CE) to resulting change in collector current (∆I_C) at constant base current (I_B) is defined as output resistance. This is denoted by r_o.

 When V_CE is increased too far, collector base junction completely breaks down and due to this avalanche breakdown, collector current increases rapidly. This is not shown in the characteristic. In this case, the transistor is damaged.

In the active region, for small values of base current, the effect of collector voltage over collector current is small while for large base currents this effect increases. The shape of characteristic here is same as that of CB transistors.

In the cut off region, a small amount of collector current flows even when base current I_B is zero. This is called I_CEO. Since the main current is also zero, the transistor is said to be cut off.

 r_o=∆V_BE/∆I_B
=700m/200µ=3.5kΩ.

r_o=∆V_CE/∆I_C
=3/0.3m=10kΩ.

The quiescent point is best located between the cut off and saturation point. I_E= V_EE/R_E, V_CB=V_CC-I_CR_L. It is denoted by ‘Q’.

The ratio of change in emitter base voltage (∆V_EB) to resulting change in emitter current (∆I_E) at constant collector base voltage (V_CB) is defined as input resistance. This is denoted by r_i.

The ratio of change in collector base voltage (∆V_CB) to resulting change in collector current (∆I_C) at constant emitter current (I_E)¬ is defined as output resistance. This is denoted by r_o.

 A graph of I_C against V_CB is drawn. The curve so obtained is known as output characteristics. The emitter current (I_E) is kept constant.

A graph of I_E against V_EB is drawn. The curve so obtained is known as input characteristics. The collector base voltage (V_BC) is kept constant.

The ratio of change in emitter base voltage (∆V_EB) to resulting change in emitter current (∆I_E) at constant collector base voltage (V_CB) is defined as input resistance. This is denoted by r_i.
We know, ∆V_EB/∆I_E=r_i
=200/5=40Ω.

 In the active region, for small values of base current, the effect of collector voltage over collector current is small while for large base currents this effect increases. The shape of characteristic here is same as that of CB transistors.

Here, the quantity collector to base voltage corresponds to the output circuit of a CB transistor. The complete electrical behaviour of a transistor can be described by stating the relation between these quantities.

The name of the CB transistor says that it’s a common based one. The input is given between the emitter and base terminals and the output is taken between collector and base terminals.

The input current flowing into the emitter terminal must be higher than the base current and collector current to operate the transistor. Therefore the output collector current is less than the input emitter current.

The input characteristics resemble the illuminated photo diode and the output characteristics resemble the forward biased diode. This transistor has low input impedance and high output impedance.