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Collector Feedback Bias

Collector Feedback Bias. ELEC 121. BJT Biasing 4. For the Collector Feedback Bias Configuration: Draw Equivalent Input circuit Draw Equivalent Output circuit Write necessary KVL and KCL Equations Determine the Quiescent Operating Point Graphical Solution using Loadlines

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Collector Feedback Bias

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  1. Collector Feedback Bias ELEC 121

  2. BJT Biasing 4 For the Collector Feedback Bias Configuration: • Draw Equivalent Input circuit • DrawEquivalent Output circuit • Write necessary KVL and KCL Equations • Determine the Quiescent Operating Point • Graphical Solution using Loadlines • Computational Analysis • Design and test design using a computer simulation ELEC 121

  3. DC Bias with Collector (Voltage) Feedback Another way to improve the stability of a bias circuit is to add a feedback path from collector to base In this bias circuit the Q-point is only slightly dependent on the transistor  ELEC 121

  4. Base – Emitter Loop Solve for IE Applying Kirchoff’s voltage law: -VCC + IERC + IBRB + VBE + IERE = 0 Since IE = ( + 1) IB then: Simplifying and solving for IE: ELEC 121

  5. Collector Emitter Loop Applying Kirchoff’s voltage law: IE RE + VCE + ICRC – VCC = 0 Since IC= IE and IE = ( + 1) IB: IE(RC + RE) + VCE – VCC =0 Solving for VCE: VCE = VCC – IE (RE + RC) ELEC 121

  6. Network Example ELEC 121

  7. Network Example ELEC 121

  8. Collector Feedback with RE = 0 ELEC 121

  9. Design of CE Amplifier with Collector Feedback Bias • Select a value for VCC • Determine the value of  from spec sheet or family of curves • Select a value for IEQ • Let VCE = ½ VCC (typical operation, 0.4 VCC≤ VC≤ 0.6 VCC) • Let VE = 0.1 VCC(for good operation, 0.1 VCC≤ VE≤ 0.2 VCC) • Calculate RE, RC and RB ELEC 121

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