© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Electronic Devices Ninth Edition Floyd Chapter 17

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Power Supply Regulation An ideal power supply provides a constant dc voltage despite changes to the input voltage or load conditions. Ideal power supply The output voltage of a real power supply changes under load as shown in the second plot. The output is also sensitive to input voltage changes. Real power supply V NL V FL

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Line Regulation Line regulation is a measure of how well a power supply is able to maintain the dc output voltage for a change in the ac input line voltage. The formula for line regulation is Line regulation can also be expressed in terms of percent change in V OUT per volt change on the V IN (%/V).

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Load Regulation Load regulation is a measure of how well a power supply is able to maintain the dc output voltage between no load and full load with the input voltage constant. It can be expressed as a percentage change in load voltage: Load regulation can also be expressed in terms of percent change in the output per mA change in load current (%/mA). Sometimes a maximum error voltage is given in the specification as illustrated in the next slide for a commercial power supply.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Load Regulation Commercial power supplies, such as you have in lab, have excellent line and load regulation specifications. The BK Precision 1651A is an example of a triple output supply (two 0-24 V outputs and a fixed 5 V output). Voltage regulation specifications for this power supply are: Line regulation: ≤0.01% +3 mV (Main supply) ≤5 mV (Fixed 5 V supply) Load regulation: ≤0.01%+3 mV (Main supply) ≤5 mV (Fixed 5 V supply)

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Load Regulation Sometimes the equivalent Thevenin resistance of a supply is specified in place of a load regulation specification. Power Supply In this case, V OUT can be found by applying the voltage divider rule: In terms of resistances, load regulation can be expressed as:

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Load Regulation A power supply has an output resistance of 25 m  and a full load current of 0.50 A to a 10.0  load. (a)What is the load regulation? (b)What is the no load output voltage? = 0.25% (a) (b) By Ohm’s law, V OUT = 5.0 V. = V

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Series Regulators Series Regulator block diagram: Basic series regulator circuit: The control element maintains a constant output voltage by varying the collector-emitter voltage across the transistor.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Series Regulators The output voltage for the series regulator circuit is: (a) What is the output voltage for the series regulator? (b) If the load current is 200 mA, what is the power dissipated by Q 1 ? (a) (b) 47 k  100 k  3.9 V 18 V 4.7 k  = 12.2 V P = VI = (18 V – 12.2 V)(0.2 A) = 1.16 W

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Series Regulators Current limiting prevents excessive load current. Q 2 will conduct when the current through R 4 develops 0.7 V across Q 2 ’s V BE. This reduces base current to Q 1, limiting the load current. The current limit is: For example, a 1.4  resistor, limits current to about 0.5 A.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Series Regulators An overload causes V R5 to drop because V OUT drops. This means that less current is needed to maintain conduction in Q 2 and the load current drops. Fold-back current limiting drops the load current well below the peak during overload conditions. Q 2 conducts when V R5 +V BE = V R4 and begins current limiting. V R5 is found by applying the voltage-divider rule:

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Shunt Regulators Shunt Regulator block diagram: Basic shunt regulator circuit: The control element maintains a constant output voltage by varying the collector current in the transistor.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Shunt Regulators Although it is less efficient than the series regulator, the shunt regulator has inherent short-circuit protection. The maximum current when the output is shorted is V IN /R 1. Shunt regulators use a parallel transistor for the control element. If the output voltage changes, the op-amp senses the change and corrects the bias on Q 1 to follow. For example, a decrease in output voltage causes a decrease in V B and an increase in V C.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Switching Regulators All switching regulators control the output voltage by rapidly switching the input voltage on and off with a duty cycle that depends on the load. Because they use high frequency switching, they tend to be electrically noisy. on/off control V OUT An increase in the duty cycle increases the output voltage.A decrease in the duty cycle decreases the output voltage.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Switching Regulators A step-down switching regulator controls the output voltage by controlling the duty cycle to a series transistor. The duty cycle changes depending on the load requirement. Because the transistor is either ON or OFF on all switching regulators, the power dissipated in the transistor is very small and the regulator is very efficient. The pulses are smoothed by an LC filter. on C charges +  + L reverses polarity off

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd C discharges +  on off L field builds Switching Regulators In a step-up switching regulator, the control element operates as a rapidly pulsing switch to ground. The switch on and off times are controlled by the output voltage. Step-up action is due to the fact the inductor changes polarity during switching and adds to V IN. Thus, the output voltage is larger than the input voltage. on off C charges  + L field collapses

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd ++ on off L field builds C discharges Switching Regulators In a voltage-inverter switching regulator, the output is the opposite polarity of the input. It can be used in conjunction with a positive regulator from the same input source. Inversion occurs because the inductor reverses polarity when the diode conducts, charging the capacitor with the opposite polarity of the input. on L field collapses ++ C charges off

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd IC Voltage Regulators Integrated circuit voltage regulators are available as series regulators or as switching regulators. The popular three-terminal regulators are often used on separate pc boards within a system because they are inexpensive and avoid problems associated with large power distribution systems (such as noise pickup). 78XX Regulators The 78XX series is a fixed positive output regulator available in various packages and with standard voltage outputs. TO-220 case D-PAK

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd IC Voltage Regulators The only external components required with the 78XX series are input and output capacitors and some form of heat sink. These IC’s include thermal shutdown protection and internal current limiting. The 78XX series are primarily used for fixed output voltages, but with additional components, they can be set up for variable voltages or currents. Heat-sink surface

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd IC Voltage Regulators The 79XX series is the negative output counterpart to the 78XX series, however the pin assignments are different on this series. Other specifications are basically the same.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd IC Voltage Regulators The LM317 is a adjustable positive output IC regulator. There is a fixed reference voltage of V between the output and adjustment terminals. There is no ground pin. The output voltage is calculated by: What is V OUT ? (Assume I ADJ = 50  A.) = 16.8 V 2 k  150  +20 V+16.8 V

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd IC Voltage Regulators IC regulators are limited to a maximum allowable current before shutting down. The circuit shown is uses an external pass transistor to increase the maximum available load current. R ext sets the point where Q ext begins to conduct: For example, if I max is 1.0 A, R ext = 0.7  What minimum power rating is required for R ext ? P = I 2 R = (1 A) 2 (0.7  ) = 0.7 W

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd IC Voltage Regulators The 78S40 is an IC containing all of the elements needed to configure a switching regulator, using a few external parts. It is a universal switching regulator subsystem because it can be configured as a step-down, step-up, or inverting regulator by the user. The data sheet shows typical circuits for these configurations. Here is the step-down configuration.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Regulator Line regulation Load regulation Linear regulator Switching regulator A electronic circuit that maintains an essentially constant output voltage with changing input voltage or load current. The percentage change in output voltage for a given change in input (line) voltage. The percentage change in output voltage for a given change in load current. A voltage regulator in which the control element operates in the linear region. A voltage regulator in which the control element operates as a switch.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd 1. The load regulation of an ideal power supply is a. 0% b. 25% c. 50% d. 100%

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd 2.A correct formula for load regulation is a. b. c. d.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd 3. An alternate way to express load regulation is in terms of the a. output resistance and the full-load resistance b. output resistance and the shorted-load resistance c. input resistance and the full-load resistance d. input resistance and the shorted-load resistance

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd 4. In the circuit shown, R 4 = 0.7 . The output current will be limited to a. 0.5 A b. 0.7 A c. 1.0 A d. 1.4 A 0.7 

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd 5. The block diagram for a series voltage regulator is shown. The yellow box represents a a. control element b. sample circuit c. error detector d. reference voltage

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd 6. The block diagram for a shunt voltage regulator is shown. The yellow box represents a a. control element b. sample circuit c. error detector d. reference voltage

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd 7. The circuit in the blue shaded area is a a. high speed switching circuit b. fold-back current limiter c. reference source d. shunt regulator

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd 8. A major advantage of all switching regulators is a. low noise b. high output impedance c. high efficiency d. all of the above

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd 9. The type of regulator circuit shown is a a. series linear b. series switching c. shunt switching d. none of the above ++ on off L field builds C discharges on L field collapses ++ C charges off

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd 10. The output voltage from a 7912 is a regulated a. +5 V b. +12 V c.  5 V d.  12 V

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Answers: 1. a 2. b 3. a 4. c 5. d 6. b 7. b 8. c 9. d 10. d