8. 8
Calculation of Average value for a Half-Wave Rectifier
π
V
θ
cos
2π
V
dθ
0
dθ
θ
sin
V
2π
1
dt
V
T
1
V
P
π
0
P
2
π
0
p
T
0
DC
=
−
=
+
=
=
17. 17
The PIV occurs at the peak of each half-cycle of the input
voltage when the diode is reverse-biased. In this circuit, the
PIV occurs at the peak of each negative half-cycle.
27. 27
Calculation of RMS value for a Full -Wave Rectifier
( )
2
V
θ
sin
θ
π
2
V
dθ
2θ
cos
1
2
1
π
V
dθ
θ
sin
V
π
1
dt
V
T
1
V
P
π
0
P
P
π
0
2
p
T
0
2
rms
2
2
0
2
2
2
2
2
1
=
−
=
−
=
=
=
28. 28
Types of Full-Wave Rectifier
◼ Center-Tapped Full Wave Rectifier
◼ Bridge Full Wave Rectifier
31. 31
Basic operation of a Center-Tapped Full-Wave Rectifier. Note that the
current through the load resistor is in the same direction during the entire
input cycle, so the output voltage always has the same polarity.
42. 42
Peak inverse voltages across diodes D3 and D4 in a bridge
rectifier during the positive half-cycle of the secondary voltage.
Thursday, November 10, 2022
43. 43
Formulas For Bridge Full Wave Rectifier
1. Vpout = Vp (sec) { for ideal case }
2. Vpout =Vp (sec) – 1.4v { for practical case }
3. PIV = Vpout { for ideal case }
4. PIV = Vpout + 0.7v { for practical case }
47. 47
Basic Principle of Power Supply Filter
◼ A power supply filter ideally eliminates the fluctuations in the output
voltage of a half wave or full wave rectifier and produces a constant level
dc voltage
◼ Filtering is necessary because electronic circuits require a constant
source of dc voltage and current to provide power and biasing for proper
operation
Ripple is a Small amount
of Fluctuations in the filter
48. 48
Capacitor Input Filter/ Pi(π) Filter
◼ A Half Wave rectifier with a capacitor–input filter is shown in figure
◼ The filter is simply a capacitor connected from the rectifier output
to ground.
◼ RL represents the equivalent resistance of a load
Dr. RS
49. 49
Operation of a half-wave rectifier with a capacitor-input filter. The current
indicates charging or discharging of the capacitor.
Thursday, November 10, 2022
50. 50
Ripple Voltage (Vr)
◼ Variation in the capacitor voltage due to the charging and
discharging is called the ripple voltage
◼ Generally, ripple is undesirable, so the smaller the ripple, the
better the filtering action
Dr. RS
Half-wave ripple voltage (green line).
51. 51
Comparison of ripple voltages for half-wave and full-wave
rectified voltages with the same filter capacitor and load and
derived from the same sinusoidal input voltage.
Thursday, November 10, 2022
52. 52
The frequency of a full-wave rectified voltage is twice that of a
half-wave rectified voltage.
Thursday, November 10, 2022
53. 53
Ripple Factor (r)
◼ Indication of the effectiveness of the filter is called the ripple factor
Dr. RS
Note: The lower the ripple factor , the better the filter.
Where Vr(pp) : peak to peak ripple voltage
VDC : average value of ripple voltage
How
54. 54
Effects of C and RL on Ripple factor
Thursday, November 10, 2022
C=1000µF C=470µF
C=100µF
R=1500Ω
R=1000Ω
R=500Ω
b) Effect on RL
a) Effect on C
The ripple factor can be lowered by increasing the value of
the filter capacitor or increasing the load resistance
55. 55
Formulas of Ripple factor for HWR & FWR
rhwr =
Vr( pp)
VDC
=
1
2 3 fRLC
Dr. RS Thursday, November 10, 2022
rfwr =
Vr(pp)
VDC
=
1
4 3 fRLC
56. 56
Formulas of Vr(pp) and VDC for a Full Wave Rectifier
with Capacitor Input Filter
Vp(rect) : unfiltered peak rectified voltage
Vr(pp) : peak to peak ripple voltage
VDC : average value of ripple voltage
Thursday, November 10, 2022