This document discusses common diode applications and basic power supply circuits. It covers half-wave and full-wave rectifiers, and how they convert alternating current to pulsating direct current. Filters are described which reduce voltage and current ripples in rectified outputs. Voltage regulators are also summarized, which maintain a constant direct current output voltage despite varying loads. Zener diodes are commonly used for voltage regulation.

1. Chapter 3
Common Diode Applications
Basic Power Supply Circuits

2. Power Supply
 A group of circuits used to convert ac to dc.
 Rectifier – Converts ac to pulsating dc.
 Filter – Reduces variations in the rectifier output.
 Voltage regulator – Maintains a constant dc output
voltage.

3. Transformers
 Transformers are described in terms of the relationship
between secondary voltage (VS) and primary voltage (VP).
 Step-up – VS is greater than VP.
 Step-down – VS is less than VP.
 Isolation – VS is approximately
equal to VP.

4. Transformer Voltage and Current
Ratios
S
P
P
S
P
S
I
I
V
V
N
N



5. Half-wave Rectifiers
 Half-wave rectifier – A diode placed in series between
a transformer (or ac line input) and its load.

6. Positive Half-wave Rectifiers
This circuit converts an
ac input to a series of
positive pulses.

7. Average Load Voltage and Current
 Average voltage (Vave) – The dc equivalent of a
voltage waveform.
 Average current (Iave) – The dc equivalent of a
current waveform.
For the output from a half-wave rectifier:

pk
V
Vave 

pk
I
Iave 

8. Negative Half-wave Rectifiers
This circuit converts an
ac input to a series of
negative pulses.

9. Peak Inverse Voltage (PIV)
Peak inverse voltage (PIV) – The maximum diode
reverse bias produced by a given circuit.
For the diode in a half-wave rectifier:
(pk)
PIV S
V


10. Full-wave Rectifier

11. Full-wave Rectifier Operation
Diodes conduct during
alternate half cycles of
the input signal.
VL(pk) is approximately
half the value of VS(pk).
The circuit produces
two positive half-cycles
for each input cycle.

12. Average Load Voltage and Current
 Average voltage (Vave) – The dc equivalent of a voltage
waveform.
 Average current (Iave) – The dc equivalent of a current
waveform.
For the output from a full-wave rectifier:

pk
2V
Vave 

pk
2I
Iave 

13. Peak Inverse Voltage (PIV)
 Peak inverse voltage (PIV) – The maximum diode
reverse bias produced by a given circuit.
For the diode in a full-wave rectifier:
(pk)
PIV S
V

(pk)
2
PIV L
V


14. Negative Full-wave Rectifiers
 The negative full-wave rectifier converts an
ac input to a series of negative pulses.

15. Full-Wave Bridge Rectifiers
 The most commonly used because:
 It does not require the use of a center-tapped transformer.
 It can be coupled directly to the ac power line.
 It produces a higher dc output than a comparable full-wave
center-tapped rectifier.

16. Bridge Rectifier Operation
 Conduction alternates between two diode pairs.

17. Calculating load voltage and
current relationships
V
7
.
0
PIV
π
2
V
4
.
1
S(pk)
ave
ave
)
(pk
ave
(pk)
)
(pk






V
R
V
I
V
V
V
V
L
L
S
L

18. Working with Rectifiers
 Rectifiers are high current circuits, so IFRB can have a
significant impact on diode forward voltage (VF ).
 Cooling is often used to minimize the effects of high
power rectifier reverse current. Components may be
cooled using a fan and/or a heat sink.
 High transformer tolerances can introduce significant
discrepancies between calculated and measured
current and voltage values.

19. Integrated Rectifiers
 Integrated Rectifier – A rectifier circuit that is etched
on a single piece of silicon (housed in a single case).
IC rectifiers are:
 Cheaper to produce
 Easier to troubleshoot
 The diodes in an IC rectifier operate at the same
temperature, so they have equal values of forward
voltage and leakage current.
 IC rectifier cases are designed to be attached easily
to a heat sink.

20. Filters
 A filter reduces the voltage and current variations
in the output from a rectifier.

21. Ripple Voltage (Vr)
 Ripple voltage (Vr) – The variation in the filter output
voltage.

22. The Basic Capacitive Filter
 The capacitor:
 charges through the
rectifier diode.
 discharges through
the load.
1
1
1
5
5
C
R
T
C
R
T
L
D
D
C



23. Surge Current
 The high initial current through a power supply.
 Surge current lasts only long enough for the
filter capacitor to charge.
B
W
S
R
R
V
I


)
pk
(
surge

24. Limiting Surge Current
Surge current can be limited by:
 Inserting a current limiting resistor between the filter
capacitor and the rectifier.
 Using a low-value filter capacitor (which shortens the
duration of the surge).
 Using an inductive filter.

25. Filter output voltages
C
t
I
V
V
V
V
L
r
r



2
pk
dc

26. Filtering and Half-wave
Rectifier PIV
)
pk
(
2
PIV S
V


27. LC Filters

28. Voltage Regulators
 Voltage regulator – The final circuit in the dc power
supply.

29. Zener Voltage Regulators

30. Regulator Response to
Load Variations

31. Zener Reduction of Vr
r
S
L
Z
L
Z
r V
R
R
Z
R
Z
V


)
||
(
||
(out)

32. A Basic DC Power Supply