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MALVINO
Electronic
PRINCIPLES
SIXTH EDITION
Diode Circuits
Chapter 4
VP
The half-wave
rectifier
Vin
Vin
Vout
VP
Vout
Ideal: VP(in) = VP(out)
Half-wave rectifier
• The dc value of the output is the
average value.
• Vdc = VP/p
• fout = fin
• Second approximation:
VP(out) = VP(in) - 0.7 V
Transformer review
• When the turns ratio (N1/N2) is greater
than 1, the primary voltage is stepped
down.
• When the turns ratio is less than 1, the
primary voltage is stepped up.
• Dotted ends have the same instantaneous
phase.
• Full-wave rectifiers require a winding
with a center tap.
The full-wave
rectifier
Vin
C.T.
Vout
Vout
Full-wave rectifier
• The dc value of the output is the
average value.
• Vdc = 2VP/p
• fout = 2fin
• The input to each diode is half the
secondary voltage.
• Second approximation:
VP(out) = VP(in) - 0.7 V
The bridge
rectifier
Vin
Vout
Vout
Bridge rectifier
• The dc value of the output is the
average value.
• Vdc = 2VP/p
• fout = 2fin
• Second approximation:
VP(out) = VP(in) - 1.4 V
The choke-input filter
L
C
Vin
RL
When XL >> XC:
Vout @
XC
XL
Vin
Vout
Discharge
The capacitor-input
filter
VP
+
0
Charge
-
I
VR =
fC
Where VR is the peak-to-peak ripple voltage
Dc output voltage drops when
load current increases
• Ac line regulation can have an effect
• Bulk resistance of rectifiers causes a
voltage drop
• Resistance of transformer windings
causes a voltage drop
• Ac ripple increases and average dc
decreases
Diode ratings
• Half-wave rectifier with capacitor-input
filter: PIV = 2VP
Idiode = Idc
• Full-wave rectifier with capacitor-input
filter: PIV = VP
Idiode = Idc
• Bridge rectifier with capacitor-input
filter: PIV = VP
Idiode = 0.5Idc
Bridge supply troubleshooting
• No output - - blown fuse, two or more
diodes open, load shorted
• Low output/extra ripple - - bad filter,
open diode, shorted winding, overload
• Full-wave signal at output - - open filter
capacitor
• Half-wave ripple frequency - - open diode
Positive clipper
RS
Vin
0.7 V
RL
Vout
Negative clipper
RS
Vin
RL
Vout
-0.7 V
Positive clamper
C
RL
Vout
-0.7 V
Stiff clamper: RLC > 100T
Negative clamper
C
0.7 V
RL
Vout
Stiff clamper: RLC > 100T
Half-wave voltage doubler
VP
D2
C1
D1
C2
2VP
Full-wave voltage doubler
VP
2VP
VP