1. Mechatronics 1
Filters & Regulators

2. Filters & Regulators Power Supply Review Rectifier Review Filters
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 Forward bias Reverse bias
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 :

11. Bias Recognition Forward Reverse Reverse Forward Forward 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. Since 2/ π = 0.637, you can calculate
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 = 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. 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.
Conductors
Dielectric

20. The Basic Capacitor Initially uncharged Source removed Fully charged
Charging
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. Universal exponential curves
Specific values for current and voltage can be read from a universal curve. For an RC circuit, the time constant is
Rising exponential
Falling exponential

30. Half Wave Rectifier with Capacitor Filter

31. First Quarter Cycle

32. Remainder of Cycle

33. Second Cycle

35. 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

37. Half Wave & Full Wave Ripple Comparison

38. 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%

39. Regulators
IC regulators
Line regulation
Load regulation

40. 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

41. A Basic Regulated Power Supply

42. 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%

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