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Dr. Ahmed ElShafee
Dr. Ahmed ElShafee, ACU : Fall 2019, Electronic Circuits I1
Lecture (04)Diode
Applications I
• The Complete Diode Model
• Add a small forward dynamic resistance (r’d) and the large internal reverse resistance (r’R).
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Example 01
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• Complete model
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Example 02
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• Complete model
Dr. Ahmed ElShafee, ACU : Fall 2019, Electronic Circuits I8
The Basic DC Power Supply
• All active electronic devices require a source of constant dc that can be supplied by a battery or a dc power supply
• dc power supply converts the standard 220V, 50Hz ac voltage available at wall outlets into a constant dc voltage
A basic block diagram of the complete power supply9
• Stage 1: transformer changes ac voltages based on the turns ratio between the primary and secondary.
• Stage 2: rectefire (half wave) The rectifier converts the ac input voltage to a pulsating dc voltage,
Dr. Ahmed ElShafee, ACU : Fall 2019, Electronic Circuits I10
• Stage 3:The filter eliminates the fluctuations in the rectified voltage and produces a relatively smooth dc voltage.
• Stage 4: The regulator is a circuit that maintains a constant dc voltage for variations in the input line voltage or in the load.
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Half wave rectifier
• When the sinusoidal input voltage (Vin) goes positive, the diode is forward‐biased and conducts current through the load resistor
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• When the input voltage goes negative during the second half of its cycle, the diode is reverse‐biased.
• There is no current, so the voltage across the load resistor is 0 V,
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• The resulted voltage drop across load is stimulating DC voltage
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Example 01
• What is the average value of the half‐wave rectified voltage in Figure
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• Effect of the Barrier Potential on the Half‐Wave Rectifier Output
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• It’s acceptable to neglect the effect of the barrier potential, when the peak value of the applied voltage is much greater than the barrier potential (at least 10 V, as a rule of thumb).
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Example 02
• Draw the output voltages of each rectifier for the indicated input voltages, as shown in Figure. The 1N4001 and 1N4003 are specific rectifier diodes.
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• Peak Inverse Voltage (PIV)
• equals the peak value of the input voltage, and the diode must be capable of withstanding this amount of repetitive reverse voltage
• A diode should be rated at least 20% higher than the PIV.
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• Transformer Coupling
• transformer is used to couple the ac input voltage from the source to the rectifier,
• Advantages:
– Step down voltage
– electrically isolated rectifier, thus preventing a shock hazard in the secondary circuit.
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• turns ratio
• If n < 1, then Vsec <Vpri.
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Example 03
• Determine the peak value of the output voltage for Figure, if the turns ratio is 0.5.
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Thanks,..
See you next week (ISA),…
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