CHAPTER 5: REGULATED DC POWER SUPPLY

Transcription

1 CHAPTER 5: REGULATED DC POWER SUPPLY Dr. Wan Mahani Hafizah binti Wan Mahmud

2 Topics in Chapter 5 5.0Introduction 5.1Rectifier 5.2Filter 5.3oltage Regulator 5.4Switching Regulator 2

3 Power Supply Block Diagram Figure 5.1 3

4 4

5 Block Function Transformer - convert the voltage from the wall outlet (AC voltage) to a lower voltage. Rectifier rectify the AC voltage to DC voltage Filter - smooth out the voltage ripple that is left after the rectification. Regulator provide a constant DC output voltage that is essentially independent of the input voltage, output load current and temperature. 5

6 Transformer A transformer consists of two coils of wire on a common iron core The voltages on these two coils are related by the turns ratio, which is the ratio of the number of turns of wire in the secondary coil to that in the primary coil. 6

7 Transformer (cont.) Transformation ratio: a = pri N = pri sec N sec For ideal transformer: (No power loss) I = pri pri = sec I sec 2 types: Step-up transformer (N sec > N pri ) Step-down transformer (N sec < N pri ) 7

8 RMS alues Note that the volts (in USA) and volts (Malaysia) are RMS values. The actual amplitude of that sinusoidal signal is a factor of 2 larger. RMS? 8 Root mean square : also known as the quadratic mean, is a statistical measure of the magnitude of a varying quantity (effective voltage)

9 RMS alues (cont.) RMS : 9 the rms value is the square root of the mean of the squares of the voltages during a complete cycle of the AC signal rms is the single DC value which will deliver the same average power as the AC signal Also known as the effective value For sinusoidal waveform: rms = p / 2 where p = m : peak voltage

10 Rectifier Circuits Basic rectifier converts an ac voltage to a pulsating dc voltage Rectifier circuits are used in virtually all electronic devices to convert the Hz ac power line source to the dc voltages required for operation of the electronic device In rectifier circuits, the diode state changes with time and a given piecewise linear model is valid only for a certain time interval A filter then eliminates ac components of the waveform to produce a nearly constant dc voltage output 10

11 Rectifier Circuits (cont.) Diodes are used in rectifier circuits because their ability to conduct current in one direction and block current in the other direction. There are two (2) types: half wave rectifier full wave rectifier bridge rectifier centre tapped transformer 11

12 12 Rectifier Diodes

13 Half-wave Rectifier : Transformer Coupled 13 p(sec) = N N sec pri p( pri)

14 Half-wave Rectifier : Transformer Coupled p = (sec) p if N N ( pri) sec = pri and if diode is ideal 14

15 15 Half-wave Rectifier

16 16 Half-wave Rectifier (cont.)

17 Half-wave Rectifier (cont.) D = 0 17 Note: There is no voltage drop across diode if it is an ideal diode ( D = 0)

18 Diode I- Characteristics Actual Characteristic Ideal Diode D = t = k D = 0 18

19 Half-wave Rectifier (cont.) D If diode is not ideal ( D 0), then the peak at the output will be m - D 19

20 Ripple Factor : Half-wave Rectifier RMS output: DC output: AC ripple output: o ( p) rms = 2 p dc = 0.318p = π = r(rms) p 20 Ripple factor: % r = = r(rms) dc p p 100 = 121%

21 Example : Half-wave Rectifier Determine the DC, rms and ripple factor for the shown circuit 21 N sec 1 sec = pri = 120 = 30 N pri 4 Assume the diode is ideal, so: rms o ( p ) = 30 2

22 Example : Half-wave Rectifier 30 2 π o( p) DC = = = π o ( p ) 30 2 rms = = = r ( rms) = 0.385o ( p) = 0.385(30 2) = r% 22 = r( rms) DC x 100% = x 100% = 121%

23 23 Full-wave : Bridge Rectifier

24 24 Full-wave Bridge Rectifier (cont.)

25 25 Full-wave Bridge Rectifier (cont.)

26 Full-wave : Centre Tapped Rectifier 26

27 Full-wave : Centre Tapped Rectifier During positive cycle: 27

28 Full-wave Centre Tapped Rectifier During negative cycle: 28

29 Full-wave : Centre Tapped Rectifier 29

30 Ripple Factor : Full-wave Rectifier RMS output: DC output: o ( p) rms = 2 2 p dc = = π p AC ripple output: r(rms) = p 30 Ripple factor: %r = = r(rms) dc p p 100 = 48.4%

31 Example : Full-wave Rectifier Determine the DC, rms, and ripple factor for the shown circuit 120 rms 50 Hz 4 : 3 R L N sec 3 sec = pri = 120 = 90 N pri 4 Assume the diode is ideal, so: rms 31 sec o ( ) = = = p

32 Example : Full-wave Rectifier 2 o( p) π 2 ( 63.64) DC = = = π o ( p ) rms = = = r ( rms) = 0.308o ( p) = 0.308(63.64) = r = r( rms) DC x 100% = x 100% = 48.4%

33 Peak Inverse oltage (PI) The peak inverse voltage (PI) equals the peak value of the input voltage The diode in the rectifier circuit must be capable of withstanding this amount of repetitive reverse voltage Peak inverse voltage (PI) rating of the rectifier diode gives the breakdown voltage of the diode The PI rating is given in the data sheet 33

34 Rectifier Diode Datasheet : Example 34

35 Summary of Rectifier Table

36 Summary of Rectifier (cont.) Half-wave 36 Full-wave