Computer & Electronic Systems
Year 1, Semester 2
Electronic Building Blocks 1
Diode Applications
Diode Applications
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Circuit Protection
Half-Wave Rectifier
Full-Wave Rectifier
Zener Voltage Reference
Diode Applications
2
Circuit Protection
• Protect circuit from being damaged due to
a reversed power supply
• When power supply is correctly
connected, the diode is forward biased
• Reversed power supply connection means
diode is reverse biased, no current passes
and no damage occurs to the circuit
Diode Applications
3
Half-Wave Rectifier
• AC voltage converted to DC voltage
• Load is represented by the resistor R
• Positive half-cycles of the input voltage
forward-bias the diode which conducts
current into R
• Negative half-cycles reverse-bias the
diode, meaning no current and the voltage
across R=0
• VAVG=VPeak/π
Diode Applications
4
Bridge Full-Wave Rectifier
• Uses 4 diodes. Current in the same direction
through R on both half-cycles
• Positive input cycle:
D1, D2: forward-biased, conduct current
D3, D4: reverse-biased
Current path A, D1, R, D2, B
• Negative input cycle:
D3, D4: forward-biased, conduct current
D1, D2: reverse-biased
Current path B, D4, R, D3, A
• VAVG=2*VPeak/π
Diode Applications
5
Zener Diodes
• Zener diode is designed for use in the
reverse breakdown region
• Voltage across diode remains constant
over wide range of reverse currents, useful
in a power supply to keep voltage steady
under various current loads
• Breakdown voltages available from 1V to
>100V
Diode Applications
6
Zener Voltage Regulation
• Provides an output reference voltage
which is stable despite changes in input
voltage
• Used to regulate voltages in reference
circuits
• Use with 9V battery (whose voltage falls
with use) to keep output steady at 5.1V
Diode Applications
7
Zener Application
• Keep bulb voltage at 6V as battery
increases to 9V – see diagram on board
• Battery 3V-6V: Zener not conducting, lamp
brightness gradually increases, all current
through lamp
• Battery 6V-9V: Zener conducts and keeps
voltage across the lamp fixed at 6V
Diode Applications
8
Power Supply
• Convert 240V AC mains voltage to 9V DC
• 4 main blocks:
1) Transformer converts 240V AC to 12V AC
2) Bridge full-wave rectifier converts 12V AC into
pulsating DC
3) RC low-pass filter to smooth out pulsating DC
4) Zener diode fixes 9V
• For mains applications, buy the power supplies,
don’t make them!!
Diode Applications
9
Typical Diode Calculations
• What is the average value of a half-wave
rectified voltage with a peak value of
200V?
• What is the average value of a full-wave
rectified voltage with a peak value of 75V?
• What is max current a Zener diode can
pass without damage if breakdown voltage
is 10V and power rating is 5W?
Diode Applications
10
Review
• PN Junction
• Diodes
• Diode Application Circuits
Diode Applications
11