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Linear Power Supply

Linear Power Supply. Outline. Linear Power Supply Poor man’s cell phone charger Small signal resistance Adjustable power supply Rectifier Circuit Half-wave rectifier circuit Full-wave rectifier circuit Full-wave rectifier circuit as a Frequency mixer Filter Circuit Rectifier Circuit.

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Linear Power Supply

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  1. Linear Power Supply

  2. Outline • Linear Power Supply • Poor man’s cell phone charger • Small signal resistance • Adjustable power supply • Rectifier Circuit • Half-wave rectifier circuit • Full-wave rectifier circuit • Full-wave rectifier circuit as a Frequency mixer • Filter Circuit • Rectifier Circuit

  3. Outline • Large-Signal and Small-Signal Operation • Application of Diodes (Up to 3.5.1)

  4. c03f19 How does a small increase in Vad affect Vout?

  5. Drop in Output Voltage

  6. c03f20 (Slope)

  7. Small Signal Resistance Small Signal Resistance: ID/VT

  8. I-V Characteristic of a 1n4001 Diode

  9. Export I-V Data to a Table

  10. Export Table

  11. Small Signal Resistance Dynamic Resistance from the measurement: (0.748-0.740)/(67.57 mA-57.89 mA)= 0.826 Ohms

  12. c03f22 Using Small Signal Model in a Small Signal Calculation

  13. c03f23

  14. Small Signal Model of Adaptor c03f25 Change in Vad

  15. How should a load be modeled? A laptop consumes an average power of 25 W with a supply voltage of 3.3 V. Determine the average current drawn from the batteries or the adaptor. P=VI I= 7.56 A If the laptop is modeled by a resistor, then RL is 0.436 Ohms.

  16. You Can’t Power a Laptop with a Circuit Like this!

  17. How should a Cellphone load be modeled? A cellphone consumes an average power of 100 mWwith a supply voltage of 2.4 V. Determine the average current drawn from the batteries or the adaptor. P=VI I= 41.6 mA If the cellphone is modeled by a resistor, then RL is 79 Ohms.

  18. Use a 79 Ohm Resistor to Model a Cell Phone Load

  19. Dual-Output Adjustable Linear Regulated Power Supply

  20. Block Diagram

  21. Simple Description • Transformer: “Downconvert” the AC line voltage to a smaller peak voltage Vm, usually about 2-3 Volts larger than the ultimately desired DC output. • Diode Rectifier Circuit: produce a waveform with large DC component. • Filter: smooth out the rectified sinusoid. • Regulator: eliminate residual ripple

  22. c03f27 c03f27

  23. c03f28 Half-Wave Rectifier Voltage offset Diode is off for Vin < VD,on Assume constant voltage model for diodes

  24. c03f29 On for Vin less than –VD,on

  25. c03f31 An AC-DC Converter Circuit Ideal Diode Model

  26. c03f30 An AC-DC Converter Circuit Constant Voltage Diode Model Issue: It remains to be seen whether it can provide a current to a load

  27. How should a load be modeled? A laptop consumes an average power of 25 W with a supply voltage of 3.3 V. Determine the average current drawn from the batteries or the adaptor. P=VI I= 7.56 A If the laptop is modeled by a resistor, then RL is 0.436 Ohms.

  28. c03f32 Rectifier Driving a Resistive Load The diode is turned on again ripples Vin begins to fall after t1 because RL provides a discharge path for C1. C1 must be sufficient large so that the current drawn by RL does not reduce Vout significantly.

  29. c03f33 C1 is called smoothing capacitor

  30. c03f34 Magnitude of the Ripple Tin (Vp-VD,on)/RL is the current discharged through RL (basic form of this equation: Q=CV)

  31. c03f35 The Maximum Forward Bias Current • Maximum Forward Current Occurs at the point when the diode turns on (t1) • C1dVout/dt is maximum • The current supplied to RL is (Vp-VD,on)/RL

  32. Screen Shots

  33. Smoothed Capacitor

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