Discrete Semiconductor Devices and Circuits

Class A BJT Amplifiers

62 questions By Tony R. Kuphaldt

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Question 13 of 62

Calculate the approximate voltage gain (A_V) for the following common-emitter amplifier circuit, and also calculate the quiescent DC voltages measured at the three terminals of the transistor with respect to ground (V_B, V_E, and V_C). Assume a silicon transistor:

A_V ≈

V_B ≈

V_E ≈

V_C ≈

Reveal answer

A_V ≈ 4.55

V_B ≈ 2.125 volts

V_E ≈ 1.425 volts

V_C ≈ 9.521 volts

Notes:
Nothing much to comment on here - just some practice on common-emitter amplifier calculations. Note that the approximations given here are based on the following assumptions:

0.7 volts drop (exactly) across base-emitter junction.

Infinite DC current gain (β) for transistor (I_B = 0 μA ; I_C = I_E).

Negligible loading of bias voltage divider by the emitter resistance.

Negligible dynamic emitter resistance (r′_e = 0 Ω )

This question lends itself well to group discussions on component failure scenarios. After discussing how to calculate the requested values, you might want to ask students to consider how these values would change given some specific component failures (open resistors, primarily, since this is perhaps the most common way that a resistor could fail).
Question 14 of 62

Calculate the approximate voltage gain (A_V) for the following common-emitter amplifier circuit, and also calculate the quiescent DC voltages measured at the three terminals of the transistor with respect to ground (V_B, V_E, and V_C). Assume a silicon transistor:

A_V ≈

V_B ≈

V_E ≈

V_C ≈

Reveal answer

A_V ≈ 7.02

V_B ≈ 2.273 volts

V_E ≈ 1.573 volts

V_C ≈ 13.96 volts

Notes:
Nothing much to comment on here - just some practice on common-emitter amplifier calculations. Note that the approximations given here are based on the following assumptions:

0.7 volts drop (exactly) across base-emitter junction.

Infinite DC current gain (β) for transistor (I_B = 0 μA ; I_C = I_E).

Negligible loading of bias voltage divider by the emitter resistance.

Negligible dynamic emitter resistance (r′_e = 0 Ω )

This question lends itself well to group discussions on component failure scenarios. After discussing how to calculate the requested values, you might want to ask students to consider how these values would change given some specific component failures (open resistors, primarily, since this is perhaps the most common way that a resistor could fail).
Question 15 of 62

Calculate the approximate voltage gain (A_V) for the following common-emitter amplifier circuit, and also calculate the quiescent DC voltages measured at the three terminals of the transistor with respect to ground (V_B, V_E, and V_C). Assume a silicon transistor:

A_V ≈

V_B ≈

V_E ≈

V_C ≈

Reveal answer

A_V ≈ 11.8

V_B ≈ -1.244 volts

V_E ≈ -0.544 volts

V_C ≈ -5.568 volts

Notes:
Nothing much to comment on here - just some practice on common-emitter amplifier calculations. Note that the approximations given here are based on the following assumptions:

0.7 volts drop (exactly) across base-emitter junction.

Infinite DC current gain (β) for transistor (I_B = 0 μA ; I_C = I_E).

Negligible loading of bias voltage divider by the emitter resistance.

Negligible dynamic emitter resistance (r′_e = 0 Ω )

This question lends itself well to group discussions on component failure scenarios. After discussing how to calculate the requested values, you might want to ask students to consider how these values would change given some specific component failures (open resistors, primarily, since this is perhaps the most common way that a resistor could fail).