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PWM Amplifier (Pulse Width Modulation)

PWM Amplifier (Pulse Width Modulation). …another application of Power Electronics. Power Affiliates Program - May 11, 2001 Robert Balog. University of Illinois at Urbana - Champaign. Classification of Amplifiers. Key difference. “Linear conduction”. “Switch action”. Conventional.

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PWM Amplifier (Pulse Width Modulation)

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  1. PWMAmplifier(Pulse Width Modulation) …another application ofPower Electronics Power Affiliates Program - May 11, 2001 Robert Balog University of Illinois at Urbana - Champaign

  2. Classification of Amplifiers

  3. Key difference “Linear conduction” “Switch action” Conventional Switching

  4. Device Ratings “Linear conduction” “Switch action” Conventional Switching

  5. Motivation: • Class D switching output is highlyefficientcompared to the Class A or Class A/B amplifier. • Each switching device is eitherconducting currentorblocking voltage. Therefore the power dissipated in the device is zero. • Physically smaller (and cheaper) components can be used.

  6. “buck” converter q(t) fixed duty ratio L & C Low Pass Filter or “average” Voutput is a constant “DC”

  7. Averaging:

  8. System Diagram

  9. Graphical construction of PWM waveform

  10. Can be a Full “H” Bridge or a Half Bridge Switch pairs (operate together): (1) SW1 & SW3 (2) SW2 & SW4 Note: if SW1 & SW4 are both closed, supply is shorted out. Dead Time circuit prevents this from occurring Typically there will be a low pass filter (LPF) before the load to filter out the high frequency carrier. In certain applications, the load may be inductive enough to act as the filter, for example, a motor.

  11. Guarantees that only one pair of switches in on, preventing “shoot through” current typical of totem pole drive circuits.

  12. Applications • Motor Drive • Servo Drive • Inverter power supply • Audio Amplifier

  13. Prototype PWM Amplifier

  14. Demonstration: PWM Audio Amplifier

  15. PWMAmplifier(Pulse Width Modulated) …another application ofPower Electronics Power Affiliates Program - May 11, 2001 Robert Balog University of Illinois at Urbana - Champaign

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