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Understanding Clamper Circuits and Applications

Feb 12, 2025

Basic Electronics - Clamper Circuits Lecture Notes

Introduction to Clamper Circuits

  • Discussion continues on clamper circuits.
  • Focus on negative level shift clamper.
  • Combining clamper and peak detector to create a voltage doubler circuit.

Negative Level Shift Clamper Circuit

  • Circuit Configuration: Similar to previous clamper, but diode polarity is reversed.
  • Ideal Diode Model:
    • V_on = 0 V
    • V_s(t) = V_m * sin(ωt) where V_m = 5 V.
    • V_s varies between +5 V and -5 V.

Observations

  1. Charging Behavior:
    • When the diode (D) conducts, the capacitor (C) charges instantaneously.
    • V_c = V_s because R_on is small, hence time constant (Ï„ = R_on * C) is also small.
  2. Capacitor Voltage Behavior:
    • V_c can only increase.
    • Maximum V_c = V_m (5 V), stays constant after reaching maximum.
  3. Output Voltage (V_o):
    • V_o(t) = V_s - V_c = V_s - V_m (negative level shift).

Waveform Analysis

  • Initially, V_c = 0. As V_s increases, D conducts, and V_c charges to V_s.
  • Once V_c reaches V_m (5 V), it remains at that value, making V_o a shifted version of V_s downwards.

Clamper with Diode Forward Voltage Drop

  • V_on = 0.7 V:
    • Capacitor voltage reaches a maximum of 4.3 V (5 V - 0.7 V).
    • Output voltage: V_o(t) = V_s - 4.3 V.
  • Result: Output voltage is clamped to 0.7 V instead of 0 V.

Voltage Doubler Circuit

  • Combination of Clamper and Peak Detector:
    • Input voltage: sinusoidal from -V_m to +V_m.
    • Clamper output: 0 to 2V_m (positive level shift).
    • Peak detector output: DC voltage of 2V_m.

Implementation

  • Components:
    • C1 and D1 form the positive clamper.
    • D2 and C2 form the peak detector.
  • Waveform Observations:
    • Input (V_i), Clamped (V_1), and Output (V_o) waveforms.

Case with V_on = 0.7 V in Voltage Doubler

  • Output is V_o = 2V_m - 1.4 V (considering two diode drops).
  • Simulation files available for running circuit analysis.

Two Diode Circuit Analysis

  • Charging and Discharging Paths:
    • Charging through D1; discharging through D2.
  • Problem Statement:
    • Analyze input waveform from -V_m to +V_m with R1, R2, and capacitor values.
  • Key Assumptions:
    • R1C and R2C are large compared to T (input waveform period).

Observations and Calculations

  • Output voltage (V_o) is nearly constant due to the slow charging and discharging of the capacitor.
  • Equation: V_o(t) = V_i(t) - V_c.

Example Calculation

  • Input voltage: -10 V to +10 V.
  • Time Intervals: T1 = 0.25 ms, T2 = 0.75 ms.
  • Component Values: R1 = 5 kΩ, R2 = 10 kΩ, C = 10 µF.
  • Validating conditions for R1C and R2C being large, confirming periodic steady-state.
  • Final capacitor voltage calculated as approximately -1.86 V.
  • Output voltage is a positive shift of V_i by 1.86 V.

Conclusion

  • Reviewed how voltage doubler works with clamper and peak detector.
  • Next class topic: Diodes in rectification (AC to DC conversion).

Note: These notes summarize the key points of clamper circuits, their analysis, and applications in voltage doubler configurations. Further details can be explored through circuit simulations and practical examples.

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