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Asked: 2023-07-23T10:08:18-04:00 In:

**12.29 A class AB output stage using a two-diode bias network as shown in Fig. 12.13 utilizes diodes having the same junction area as the output transistors. At a room temperature of about 20°C the quiescent current is 1 mA and . Through a manufacturing error, the thermal coupling between the output transistors and the biasing diode-connected transistors is omitted. After some output activity, the output devices heat up to 70°C while the biasing devices remain at 20°C. Thus, while the VBE of each device remains unchanged, the quiescent current in the output devices increases. To calculate the new current value, recall that there are two effects: IS increases by about 14%/°C and VT = kT/q changes, where T = 273° + temperature in °C, and VT = 25 mV only at 20°C. However, you may assume that βN remains almost constant. This assumption is based on the fact that β increases with temperature but decreases with current. What is the new value of IQ? If the power supply is ±20 V, what additional power is dissipated? If thermal runaway occurs, and the temperature of the output transistors increases by 10°C for every watt of additional power dissipation, what additional temperature rise and current increase result?

Venkyelectrical
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**12.29 A class AB output stage using a two-diode bias network as shown in Fig. 12.13 utilizes diodes having the same junction area as the output transistors. At a room temperature of about 20°C the quiescent current is 1 mA and . Through a manufacturing error, the thermal coupling between the output transistors and the biasing diode-connected transistors is omitted. After some output activity, the output devices heat up to 70°C while the biasing devices remain at 20°C. Thus, while the VBE of each device remains unchanged, the quiescent current in the output devices increases. To calculate the new current value, recall that there are two effects: IS increases by about 14%/°C and VT = kT/q changes, where T = 273° + temperature in °C, and VT = 25 mV only at 20°C. However, you may assume that βN remains almost constant. This assumption is based on the fact that β increases with temperature but decreases with current. What is the new value of IQ? If the power supply is ±20 V, what additional power is dissipated? If thermal runaway occurs, and the temperature of the output transistors increases by 10°C for every watt of additional power dissipation, what additional temperature rise and current increase result?

**12.29 A class AB output stage using a two-diode bias network as shown in Fig. 12.13 utilizes diodes having the same junction area as the output transistors. At a room temperature of about 20°C the quiescent current is 1 mA and . Through a manufacturing error, the thermal coupling between the output transistors and the biasing diode-connected transistors is omitted. After some output activity, the output devices heat up to 70°C while the biasing devices remain at 20°C. Thus, while the VBE of each device remains unchanged, the quiescent current in the output devices increases. To calculate the new current value, recall that there are two effects: IS increases by about 14%/°C and VT = kT/q changes, where T = 273° + temperature in °C, and VT = 25 mV only at 20°C. However, you may assume that βN remains almost constant. This assumption is based on the fact that β increases with temperature but decreases with current. What is the new value of IQ? If the power supply is ±20 V, what additional power is dissipated? If thermal runaway occurs, and the temperature of the output transistors increases by 10°C for every watt of additional power dissipation, what additional temperature rise and current increase result?

microelectronics by sedra & smith chapter 12 questions

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