EE 332 Lecture 13 2019.pdf - EE 332 Devices and Circuits II Lecture#13 ©UWECE TC Chen BJT CIRCUIT ANALYSIS/4-RESISTOR BIASING CIRCUIT VCC=12 V Problem

# EE 332 Lecture 13 2019.pdf - EE 332 Devices and Circuits II...

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4/22/2019 1 ©UWECE TC Chen EE 332: Devices and Circuits II Lecture #13 ©UWECE TC Chen BJT CIRCUIT ANALYSIS / 4-RESISTOR BIASING CIRCUIT Problem : Find operation point ( 𝐼 𝐶 , 𝑉 ?? ) Given : ?1 = {𝑉 ???? = 0.7 V, 𝑉 ????? = 0.2 V 𝛽 ? = 100, 𝛽 ? = 0.5} ? 1 = 18 k , ? 2 = 36 k ? ? = 10 k , ? ? = 10 k V CC =12 V Q1 R 1 R 2 R C R E
4/22/2019 2 ©UWECE TC Chen BJT CIRCUIT ANALYSIS / 4-RESISTOR BIASING CIRCUIT V CC =12 V Q1 R 1 R 2 R C R E ANSWER An initial simplification is to Thevenize LHS: R EQ V EQ 𝑉 ?? = 𝑉 ?? ? 1 ? 1 + ? 2 = 4.0 V ? ?? = ? 1 ∥ ? 2 = 12 kΩ ©UWECE TC Chen BJT CIRCUIT ANALYSIS / 4-RESISTOR BIASING CIRCUIT Since 𝑉 ?? = 4.0 V > 𝑉 ???? = 0.7 V 𝐼 ? will flow into the base and Q1 will be conducting. So 𝑉 ?? = 𝑉 ???? = 0.7 V Assume BJT operates in forward active: KVL around the base loop: 𝑉 ?? = 𝐼 ? ? ?? + 𝑉 ??,?? + 𝐼 ? ? ? For Forward active region: 𝐼 ? = 𝛽 ? 𝐼 ? ∴ 𝑉 ?? = 𝐼 ? ? ?? + 𝑉 ??,?? + 𝐼 ? 𝛽 ? + 1 ? ? V CC =12 V Q1 R C R E ANSWER

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