Review EEE118: Electronic Devices and Circuits 1 Finished looking at - PDF document

EEE118: Lecture 7 Review EEE118: Electronic Devices and Circuits 1 Finished looking at the peak detector circuit. Lecture VII 2 Considered the use of the peak detector in AM radio demodulation 3 Introduced and described the operation of the diode voltage James Green clamp circuit. The clamp can be broken down into, 0 ° - ∼ 180 ° - Diode not conducting, negligible charging of C Department of Electronic Engineering University of Sheffield through R. j.e.green@sheffield.ac.uk 180 ° - ∼ 270 ° - Diode conducts C charges through D. 270 ° - ∼ 360 ° - Diode not conducting, small discharge current flows from C through R. All following cycles - Diode briefly conducts around ∼ 270 ° to recharge C 4 Connected a peak detector to a voltage clamp to form a peak to peak detector 2/ 20 1/ 20 EEE118: Lecture 7 EEE118: Lecture 7 Review Continued Outline 1 Simulation Programs Considered the equilibrium condition that defines how ideally SPICE the peak to peak detector acts as a voltage doubler QsapecNG Developed a three stage voltage doubler and looked at the voltage on the clamp and peak detector at each stage. 2 Rectifiers: Linear Power Supplies Observed that the voltage doubler is often drawn as a ladder 3 Single and Three Phase Supply in which capacitors are the “edges” and diodes are the “rungs” 4 Half Wave Rectifier 5 Capacitive Smoothing Choosing a Capacitor 6 Review 7 Bear 3/ 20 4/ 20 EEE118: Lecture 7 EEE118: Lecture 7 Simulation Programs Simulation Programs SPICE QsapecNG S imulation P rogram with I ntegrated C ircuit E mphasis Q t-based S ymbolic A nalysis P rogram for E lectric C ircuits An open source numerical circuit simulation tool that was ( N ew G eneration) developed at the of University of California. Linear technology released LTSpice An open source analytical (i.e. symbolic) linear circuit simulation http://www.linear.com/designtools/software/#LTspice tool that is being developed at the University of Florance Example files from this course will be available on http://qsapecng.sourceforge.net/ http://hercules.shef.ac.uk/eee/teach/resources/eee118/eee118.html Example files from this course will be available on http://hercules.shef.ac.uk/eee/teach/resources/eee118/eee118.html 5/ 20 6/ 20

EEE118: Lecture 7 EEE118: Lecture 7 Rectifiers: Linear Power Supplies Single and Three Phase Supply Other descriptive terms applied to rectifier circuits are single phase Linear Power Supplies and three phase. These terms relate to the nature of the AC power supply. Most medium/heavy industry (kilowatts and above) is Rectification supplied by a three phase AC power source while light industrial applications are more likely to be supplied by a single phase source. Conversion of AC voltage into a unipolar voltage that is usually of Domestic dwellings are supplied by a single phase source. Only the form of a DC component with a superimposed AC component. single phase circuits are examinable. The DC component is always the average value of the rectifier 400 339 sin( ω t + 0) output voltage and the superimposed AC component, which is 300 339 sin( ω t + π 3 ) rarely sinusoidal, is called the ripple voltage. 200 339 sin( ω t + 2 π 3 ) Voltage [V] 100 In this course the ripple voltage will always be the peak to 0 peak value of the superimposed AC component. − 100 Rectifier circuits are often divided into two categories half wave − 200 and full wave. In fact, full wave circuits can be looked at as two or − 300 more half wave circuits connected together. − 400 0 5 10 15 20 25 30 35 40 45 50 55 60 Time [ms] 7/ 20 8/ 20 EEE118: Lecture 7 EEE118: Lecture 7 Single and Three Phase Supply Half Wave Rectifier Single phase in the UK is 240 V RMS, 50 Hz. The standard gives Half Wave Rectifier 230 V ± 10% at 50 Hz ± 0.5 Hz (BS 7671) 1 , 2 . In practice 230 V is D 1 quoted so the UK conforms with western Europe, but since 240 V A I The diode conducts I falls within the permissible limits the UK has not changed its when the voltage at A is V in V p V s R 1 V o generation voltage. more than 0.7 V positive with respect to B. 400 B Min Voltage 300 Positive half-cycles of the Std Voltage Max Voltage 25 0 . 5 200 secondary winding 20 0 . 4 Voltage [V] 100 current pass through the 15 0 . 3 0 10 0 . 2 diode. Negative Voltage [V] Current[A] 5 0 . 1 − 100 half-cycles are blocked. 0 0.0 − 200 − 5 − 0 . 1 If the orientation of the − 10 − 0 . 2 − 300 − 15 − 0 . 3 diode was reversed the − 400 − 20 − 0 . 4 0 2 4 6 8 10 12 14 16 18 20 negative half cycles − 25 − 0 . 5 Time [ms] 0 10 20 30 40 would pass and the Time [ms] 1Kitcher, C., Practical guide to inspection, testing and certification of electrical installations : conforms to positive ones would be 17th edition IEE Wiring Regulations (BS 7671:2008) and Part P of Building Regulations , Oxford: Newnes, 2009, 621.31924 (K) Red: I , Black: V o , Blue: V in blocked. 2 http://www.tlc-direct.co.uk/Book/1.1.htm 9/ 20 10/ 20 EEE118: Lecture 7 EEE118: Lecture 7 Half Wave Rectifier Capacitive Smoothing Capacitive Smoothing There is a limited range of power supply applications in which this wave shape is acceptable. The simplest method is to use a capacitor in parallel with the load resistance to store charge when the diode is conducting, and Most electronic equipment requires a relatively smooth supply voltage that approximates continuous DC (e.g. a battery) deliver charge to the resistor when the diode is not conducting. 25 1 . 5 V o for the half-wave rectifier is unipolar (no negative part, 20 1 . 2 15 0 . 9 only positive in this case). 10 0 . 6 D 1 I D Voltage [V] Current[A] 5 0 . 3 The average value (the DC component) is positive, but the I R 0 0.0 I C ripple (AC component) is large. − 5 − 0 . 3 V p V in V s C 1 R 1 V o − 10 − 0 . 6 For the circuit to be useful as a DC power source for most − 15 − 0 . 9 − 20 − 1 . 2 electronic circuits, the output may be smoothed to reduce the − 25 − 1 . 5 0 10 20 30 40 amplitude of the AC component or “ripple voltage” Time [ms] This is a peak detector circuit. C is charged in the vicinity of the There are various ways in which smoothing can be achieved. peak of every positive half cycle and provides current for the load Each requires the storage of energy so that it can be in between the positive peaks. Note the remaining ripple redistributed more evenly across the cycle - essentially filling (somewhat exaggerated in the diagram) is a good approximation in the gaps. to a triangle - this will simplify calculations later. 11/ 20 12/ 20