Question

The transfer characteristic of n-p-n transistor in CE configuration is shown in the figure.

1. Identify the cut off region, active region, saturation region from the figure.

2. In which of these regions, a transistor is said to be switched off.

3. For a CE transistor amplifier, the audio signal voltage across collector resistance of 2.0 kΩ is 2.0 V. Suppose the current amplification factor of the transistor is 100. What should be the value of R_B in series with V_BB supply of 2.0 V, if DC base current has to be 10 times the signal current?

4. In the working of a transistor, the emitter base (EB) junction is forward biased while collector base (CB) junction is reverse biased. Why?

Answer 1

1. I – cut off region 

II – active region 

III-saturation region

2.  Region I

3.  I_c = \(\frac{2}{2000} =1mA,β=\frac{I_c}{I_b}\) ,

∴ I_b = \(\frac{I_c}{β}=\frac{1mA}{100}\) = 10^-5A

I_dc =10^-5 × 10 = 10^-4A

V_bb = V_be + I_bR_b

∴ R_b = \(\frac{V_{bb}-V_{bc}}{I_{bb}}=\frac{2-0.6}{10^{-4}}\) = 14kΩ

4. Only forward biased emitter base junction can send the majority charge carriers from emitter to base and only reverse biased collector can collect these majority charge carriers form the base region.