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Ripple factor

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  • 1. Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Chapter 18: Power Supplies (Voltage Regulators)
  • 2. Slide 1 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Power Supply Diagram
  • 3. Slide 2 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Filter Circuits The output from the rectifier section is a pulsating DC. The filter circuit reduces the peak-to- peak pulses to a small ripple voltage.
  • 4. Slide 3 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Ripple Factor After the filter circuit a small amount of AC is still remaining. The amount of ripple voltage can be rated in terms of Ripple Factor (r). [Formula 18.1]100 Vdc (rms)V voltagedc (rms)voltageripple %r r 
  • 5. Slide 4 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Half-wave Rectifier Ripple Factor DC output: AC Ripple output: Ripple Factor: (Note Vm is the peak rectifier output voltage.) [Formula 18.3] [Formula 18.4] [Formula 18.5] 0.318VmVdc  0.385Vm(rms)Vr  121%100 0.318Vm 0.385Vm 100 Vdc (rms)V %r r 
  • 6. Slide 5 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Full-wave Rectifier Ripple Factor DC output: AC Ripple output: Ripple Factor: The full-wave rectifier has a significantly lower ripple factor. [Formula 18.6] [Formula 18.7] [Formula 18.8] 0.636VmVdc  0.308Vm(rms)Vr  %48100 0.636Vm 0.308Vm 100 Vdc (rms)V %r r 
  • 7. Slide 6 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Types of Filter Circuits •Capacitor Filter •RC Filter
  • 8. Slide 7 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Capacitor Filter
  • 9. Slide 8 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Ripple Voltage with a Capacitor Filter The larger the capacitor the smaller the ripple voltage. A capacitor significantly reduces the AC content of the rectified signal. Ripple Voltage: [Formula 18.9] CR 2.4Vdc C 2.4Idc fC34 Idc (rms)V L r 
  • 10. Slide 9 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. DC Output with a Capacitor Filter A capacitor increases the DC output. Dc Output: Note: Vm = peak rectified voltage IDC is the load current in mA. [Formula 18.10] C 4.17Idc Vm 4fC Idc VmVdc 
  • 11. Slide 10 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Ripple Factor with a Capacitor Filter The capacitor reduces the ripple factor. Ripple Factor: [Formula 18.11]100 CR 2.4 100 CVdc 2.4Idc 100 Vdc (rms)V %r L r 
  • 12. Slide 11 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Diode Ratings with Capacitor Filter The size of the capacitor increases the current drawn through the diodes. The larger the capacitance, the greater the amount of current. Peak Current vs. Capacitance: C = capacitance V = change in capacitor voltage during charge/discharge t = the charge/discharge time A smaller capacitor will reduce the peak current through the diodes. t CV I 
  • 13. Slide 12 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. RC Filter Circuit Adding an RC section will further reduce the ripple voltage and decrease the surge current through the diodes.
  • 14. Slide 13 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Ripple Voltage in an RC Filter Circuit The ripple voltage is significantly reduced by the addition of an RC circuit. Ripple Voltage: [Formula 18.14] Vr(rms) = ripple voltage after the RC filter Vr(rms) = ripple voltage before the RC filter R = resistor in the added RC filter XC = reactance of the capacitor in the added RC filter (rms)V R X (rms)V r C r 
  • 15. Slide 14 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Voltage Regulation The amount of variation in DC output voltage due to varying loads from no-load to full-load is called voltage regulation. Voltage Regulation: [Formula 18.2] VNL = no-load voltage VFL = full-load voltage 100% V VV %VR FL FLNL   
  • 16. Slide 15 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Voltage Regulation Circuits There are two common types of circuitry for voltage regulation: A.Discrete Transistors B. IC’s
  • 17. Slide 16 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. A. Discrete Transistors 1. Series Voltage Regulation Circuit 2. Current Limiting Circuit 3. Shunt Voltage Regulation Circuit
  • 18. Slide 17 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 1. Series Voltage Regulation Circuit The series element controls the amount of the input voltage that gets to the output. If the output voltage increases (or decreases), the comparator circuit provides a control signal to cause the series control element to decrease (or increase) the amount of the output voltage.
  • 19. Slide 18 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Series Voltage Regulation Circuit Sample Circuit R1 and R2 act as the sampling circuit ~ Zener provides the reference voltage ~ Q2 controls the base current to Q1. ~ Q1 maintains the constant output voltage If the output increases ~ The voltage through R1 and R2 increases at V2, VBE of Q2 increases, causing Q2 to conduct more, and making less available to Q1, which conducts less ~ output voltage decreases. If the output voltage decreases ~ the opposite happens.
  • 20. Slide 19 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Series Voltage Regulation Circuit Sample Circuit An op-amp is used as the comparator circuit The op-amp compares the Zener diode voltage to the output voltage (via R1 and R2) and controls the conduction of Q1.
  • 21. Slide 20 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 2. Current-Limiting Circuit As IL increases, the voltage drop across RSC (short circuit sensing R) increases. When the voltage across RSC is large enough, it drives Q2 on, diverting current away from the base of Q1, thereby reducing current through Q1 and the load.
  • 22. Slide 21 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 3. Shunt Voltage Regulation Circuit The shunt voltage regulator shunts current away from the load. The load voltage is sampled and fed back to a comparator circuit. If the load voltage is too high, control circuitry shunts more current away from the load.
  • 23. Slide 22 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 3. Shunt Voltage Regulation Sample Circuit If the voltage across the load increases above the Zener voltage, Q2 turns on, which causes Q1 to conduct and current is shunted away through Q1.
  • 24. Slide 23 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 3. Shunt Voltage Regulation Sample Circuit The op-amp acts as a comparator circuit. If the load voltage exceeds the Zener voltage, Q1 turns on and shunts current away from the load.
  • 25. Slide 24 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. B. IC Voltage Regulators Regulator ICs contain: •Comparator circuit •Reference Voltage •Control circuitry •Overload protection
  • 26. Slide 25 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. IC Voltage Regulator Types Three-Terminal Voltage Regulators 1. Fixed Positive Voltage Regulator 2. Fixed Negative Voltage Regulator 3. Adjustable Voltage Regulator
  • 27. Slide 26 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Three-Terminal Voltage Regulators The specifications for this IC indicate •the range of input voltages that can be regulated for a specific output voltage and load current range •load regulation: variation in output voltage with variations in load current •line regulation: variation in output voltage with variations in input voltage
  • 28. Slide 27 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 1. Fixed Positive Voltage Regulator These ICs provide a fixed positive output voltage.
  • 29. Slide 28 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 2. Fixed Negative Voltage Regulator These ICs output a fixed negative output voltage.
  • 30. Slide 29 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. 3. Adjustable Voltage Regulator These regulators have adjustable output voltages. The output voltage is commonly selected using a potentiometer.
  • 31. Slide 30 Robert Boylestad Digital Electronics Copyright ©2002 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Practical Power Supplies •DC Supply (Linear Power Supplies) •Chopper Supply (Switching Power Supplies) •TV Horizontal High Voltage Supply •Battery Charger Circuits