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Mechatronics 1

Mechatronics 1 . Filters & Regulators. Filters & Regulators. Power Supply Review transformer rectifier filter regulator Rectifier Review diode review half wave operation center tap full wave operation bridge operation Filters capacitor review RC time constant review

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Mechatronics 1

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  1. Mechatronics 1 Filters & Regulators

  2. Filters & Regulators • Power Supply Review • transformer • rectifier • filter • regulator • Rectifier Review • diode review • half wave operation • center tap full wave operation • bridge operation • Filters • capacitor review • RC time constant review • capacitor filter operation • ripple voltage • Regulators • IC regulators • line regulation • load regulation • zener diodes

  3. Power Supply Overview

  4. Power Supply Overview • Transformer – sets the appropriate voltage level • Rectifier – rectifies AC input voltage to pulsating DC voltage (can be half wave or full wave rectified • Filter – eliminates fluctuations in the rectified voltage and produces a relatively smooth AC voltage (this function was performed by the capacitor in the last part of Lab 5) • Regulator – maintains a constant voltage despite variations in the input line voltage or the load

  5. Power Supply Overview

  6. Rectifier Review • Diode review • Half wave operation • Center tap full wave operation • Bridge operation

  7. Diode Review • Key things to remember: • General • P material is the anode • N material is the cathode • Forward bias • the applied voltage is more negative at the cathode with respect to the anode • if barrier voltage is overcome, current will flow • acts like a closed switch • Reverse bias • the applied voltage is more negative at the anode with respect to the cathode • no current will flow (unless breakdown voltage is achieved – zener diode) • acts like an open switch

  8. Forward bias When a pn junction is forward-biased, current is permitted. The bias voltage pushes conduction-band electrons in the n-region and holes in the p-region toward the junction where they combine. p-region n-region The barrier potential in the depletion region must be overcome in order for the external source to cause current. For a silicon diode, this is about 0.7 V. p n R - + VBIAS The forward-bias causes the depletion region to be narrow.

  9. Reverse bias When a pn junction is reverse-biased, the bias voltage moves conduction-band electrons and holes away from the junction, so current is prevented. p-region n-region The diode effectively acts as an insulator. A relatively few electrons manage to diffuse across the junction, creating only a tiny reverse current. p n R - + VBIAS The reverse-bias causes the depletion region to widen.

  10. The P-N Junction • “The polarity of applied voltage which causes charge to flow through the diode is called Forward Bias.” “The polarity of applied voltage which can't produce any current is called Reverse Bias.” Source : http://www.st-and.ac.uk/~www_pa/Scots_Guide/info/comp/passive/diode/diode.htm

  11. Bias Recognition Forward Reverse Reverse Forward Forward Forward Reverse Forward

  12. Bias Recognition Reverse Forward Reverse

  13. Half Wave Rectifier

  14. Average Voltage Value • the average voltage is a measure of the efficiency of the rectifier circuit • the “straight line” dc equivalent of the pulsating dc created by half wave rectification • the value you would measure on a dc voltmeter • V p(out) • V AVG = ---------- • π

  15. Center Tapped Full Wave Rectifier

  16. Bridge Full Wave Rectifier

  17. Average Voltage Value • twice that of half wave rectified output • 2V p(out) • V AVG = ---------- • π • Since 2/ π = 0.637, you can calculate • V AVG = 0.637 V p(out) • The full wave rectifier is twice as efficient as the half wave rectifier

  18. Filters • Capacitor review • RC time constant review • Capacitor filter operation • Ripple voltage

  19. Conductors The Basic Capacitor Capacitors are one of the fundamental passive components. In its most basic form, it is composed of two conductive plates separated by an insulating dielectric. The ability to store charge is the definition of capacitance. Dielectric

  20. Initially uncharged Source removed Fully charged Charging The Basic Capacitor The charging process… A capacitor with stored charge can act as a temporary battery.

  21. Charging

  22. Discharging

  23. How fast does a capacitor charge or discharge?

  24. The RC time constant When a capacitor is charged through a series resistor and dc source, the charging curve is exponential.

  25. Capacitor Charging Voltage Curve

  26. Tau (T) • The voltage across a capacitor cannot change instantaneously because a finite time is required to move charge from one plate to another • The rate at which the capacitor charges or discharges is determined by the RC time constant of the circuit • The time constant of a series RC circuit is a time interval that equals the product of the resistance and capacitance • T = RC

  27. The RC time constant When a capacitor is discharged through a resistor, the discharge curve is also an exponential. (Note that the current is negative.)

  28. Capacitor Discharging Voltage Curve

  29. Rising exponential Falling exponential Universal exponential curves Specific values for current and voltage can be read from a universal curve. For an RC circuit, the time constant is

  30. Half Wave Rectifier with Capacitor Filter

  31. First Quarter Cycle

  32. Remainder of Cycle

  33. Second Cycle

  34. Ripple Voltage • the variation in the output voltage • much improved when you add filtering • the smaller the ripple, the better the filtering and the better quality dc output

  35. Half Wave & Full Wave Ripple Comparison

  36. Ripple Voltage • Make RC > 10T • The ripple factor (r) is an indication of the effectiveness of the filter and is defined as the ratio of the ripple voltage (Vr) to the dc (average) value of the filter output voltage (VDC) • r = (Vr / VDC) x 100%

  37. Regulators • IC regulators • Line regulation • Load regulation

  38. IC Regulators • Filters reduce ripple from a power supply to a relatively low level (<10%) • Integrated circuit regulators connect to the output of a filtered regulator and reduce the ripple to a negligible level • Regulators maintain a constant output voltage despite changes in the input voltage, load current or temperature • Available in a variety of voltages

  39. A Basic Regulated Power Supply

  40. Percent Regulation • Regulation as a percentage is a figure of merit used to measure performance of a voltage regulator • Line Regulation • How much change occurs in the output voltage for a given change in the input voltage • Line Regulation = (ΔVOUT / ΔVIN)100% • Load Regulation • How much change occurs in the output voltage from no load to full load • Load Regulation = (VNL – VFL / VFL)100%

  41. Measures • Efficiency – Average Voltage Value (VAVG) • Filter Quality – Ripple Voltage (Vr) & Ripple Factor (r) • Regulator Quality – Line & Load Regulation

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