Electronics Technology Fundamentals Chapter 25 Discrete and Integrated Voltage Regulators

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Voltage Regulation: An Overview – P1 Voltage Regulator – reduces the ripple in the filtered dc output and maintains a relatively constant output voltage despite predictable variations in load demand

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Voltage Regulation: An Overview – P2 Voltage Regulator (Continued)

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Voltage Regulation: An Overview – P3 Ideal Voltage Regulator

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Voltage Regulation: An Overview – P4 Line Regulation Change in output voltage that occurs per unit change in input voltage The lower the line regulation of a voltage regulator, the higher the quality of the circuit where  V out =the change in output voltage (usually in microvolts or millivolts)  V in =the change in input voltage (usually in volts)

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Voltage Regulation: An Overview – P5 Load Regulation Change in regulator output voltage per unit change in load current The lower the load regulation rating of a voltage regulator, the higher the quality of the circuit where  V NL =the no-load output voltage (i.e., the output voltage when the load is open)  V FL =the full-load output voltage (i.e., the load current demand is at its maximum value)  I L =the change in load current demand

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Voltage Regulation: An Overview – P6 A Combined Regulation Rating Some manufacturers combine the line regulation and load regulation For example, one voltage regulator has the following ratings: V in = 12 to 24 V dc I L = 40 mA (maximum) Regulation = 0.33% These ratings indicate that the output voltage of the regulator will vary by no more than 0.33% as long as V in remains between 12 and 24 V dc and load current does not exceed 40 mA

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Voltage Regulation: An Overview – P7 Types of Regulators Series Regulator Shunt Regulator

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Series Voltage Regulators – P1 Series Regulators – circuits that have one or more devices placed in series with the load Pass-Transistor Regulator – a circuit that uses a series transistor to regulate load voltage

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Series Voltage Regulators – P2 Pass-Transistor Regulator (Continued) An increase in V L causes V BE to decrease, which reduces conduction through the pass transistor and a relatively constant load voltage is maintained A decrease in V L causes V BE to increase, which increases conduction through the pass transistor and a relatively constant load voltage is maintained Problem: As input voltage or load current increases, the zener diode must dissipate a relatively high amount of power – reduced by using a Darlington pass-transistor regulator

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Series Voltage Regulators – P3 Darlington Pass-Transistor Regulator – a circuit that uses a Darlington pair in place of a single pass-transistor

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Series Voltage Regulators – P4 Series Feedback Regulator – a series regulator that uses an error detection circuit to provide improved line and load regulation characteristics Insert Figure 25.6

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Series Voltage Regulators – P5 Series Feedback Regulator (Continued) Insert Figure 25.7

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Series Voltage Regulators – P6 Short-Circuit Protection Pass-transistor could be destroyed by excessive current if the load is shorted Current-limiting prevents this potential problem

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Series Voltage Regulators – P7 Short-Circuit Protection (Continued)

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Shunt Voltage Regulators – P1 Shunt Regulator – a circuit that has a regulating transistor in parallel with the load Shunt Feedback Regulator – a circuit that uses an error detection circuit to control the conduction through a shunt regulator transistor

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Shunt Voltage Regulators – P2 Shunt Feedback Regulator (Continued)

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Shunt Voltage Regulators – P3 Overvoltage Protection Shunt regulator must be protected from input overvoltage conditions A crowbar circuit can be added to the input side of the regulator to protect the regulator Crowbar – a fail-safe circuit that is designed to protect a voltage-sensitive load (or circuit) from excessive input voltages

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Linear IC Voltage Regulators – P1 Linear IC Voltage Regulator – a device that is used to hold the output voltage from a dc power supply relatively constant over a specified range of line and load variations

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Linear IC Voltage Regulators – P2 Basically Four Types Fixed-Positive – provide a specific positive voltage Fixed-Negative – provide a specific negative voltage Adjustable – can be adjusted within a specified range of values Dual-Tracking – provides equal positive and negative output voltages

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Linear IC Voltage Regulators – P3 IC Regulator Specifications

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Linear IC Voltage Regulators – P4 IC Regulator Specifications (Continued) Dropout Voltage: the minimum allowable difference between input voltage and the rated output Quiescent Current (I B ): the portion of the regulator input current not delivered to the load Ripple Rejection (RR): the ratio of regulator input to output ripple, usually given in dB

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Linear IC Voltage Regulators – P5 Adjustable Regulators – Example LM317

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Linear IC Voltage Regulators – P6 Input/Output Voltage Differential (V d ) – the maximum difference between V in and V out that can occur without damaging the device where V in(max) =the maximum allowable unrectified dc input voltage V out(adj) =the adjusted output voltage of the regulator V d =the input/output voltage differential rating of the regulator

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Linear IC Voltage Regulators – P7 Output Voltage Adjustment – the potentiometer in the LM317 adjust circuit is used to set the value of the output voltage

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Linear IC Voltage Regulators – P8 Linear IC Regulator Applications: A Complete Dual-Polarity Power Supply

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Linear IC Voltage Regulators – P9

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Switching Regulators – P1 Switching Regulator – a circuit that is designed so that the current path between the regulator input and the load is not continuous Insert Figure 25.15

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Switching Regulators – P2 Switching Regulator Operation – when the control circuit senses a change in the output voltage, it sends a signal to the switch driver

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Switching Regulators – P3 Controlling Power Switch Conduction The power switch is constantly driven back and forth between saturation and cutoff Average voltage at the emitter of the power switch is found as

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Switching Regulators – P4 Pulse-Width Modulation (PWM) – used to vary the pulse width of a rectangular waveform without affecting its total cycle time Insert Figure 25.17

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Switching Regulators – P5 Variable Off- Time Modulation – the pulse width of the control voltage is fixed and the total cycle time is variable Insert Figure 25.18

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Switching Regulators – P6 Switching Regulator Configurations Step-down Regulator – dc load voltage is less than (or equal to) its rectified input voltage Step-up Regulator – dc load voltage is greater than its rectified input voltage Induced voltage across L 1 adds to the value of V in Voltage-inverting Regulator – reverses the polarity of its rectified input voltage Insert Figure a & b

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Switching Regulators – P7 IC Switching Regulators – control functions and power switching are handled by a single IC – Example: Motorola MC34063 Designed to produce 12 V/750 mA output with a 36 V rectified input Very Efficient: 89.5%

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Switching Regulators – P8

Electronics Technology Fundamentals, 3 rd ed. Paynter and Boydell © 2009 Pearson Higher Education, Upper Saddle River, NJ All Rights Reserved Switching Regulators – P9 Switching Regulators: Advantages and Disadvantages Advantages Higher efficiency than linear regulators Built in a variety of configurations – linear regulators can only be designed as step-down regulators Disadvantages Power switch generates a significant amount of noise Slower to respond to a change in load demand Design far more complex and time consuming