Electronic Fundamental Muhammad Zahid BS Regular 11 March, 17 Rectifier Lecture - 4 Electronic Fundamental Muhammad Zahid

Sine waves The sinusoidal waveform (sine wave) is the fundamental alternating current (ac) and alternating voltage waveform. Electrical sine waves are named from the mathematical function with the same shape.

Sine waves A wave is a disturbance. Unlike water waves, electrical waves cannot be seen directly but they have similar characteristics. All periodic waves can be constructed from sine waves, which is why sine waves are fundamental. 3

Sine waves A The amplitude (A) of this sine wave is 20 V T Sine waves are characterized by the amplitude and period. The amplitude is the maximum value of a voltage or current; the period is the time interval for one complete cycle. Example A The amplitude (A) of this sine wave is 20 V T The period is 50.0 ms

Sine waves The period of a sine wave can be measured between any two corresponding points on the waveform. T T T T A T T By contrast, the amplitude of a sine wave is only measured from the center to the maximum point.

Frequency Frequency ( f ) is the number of cycles that a sine wave completes in one second. Frequency is measured in hertz (Hz). Example If 3 cycles of a wave occur in one second, the frequency is 3.0 Hz 1.0 s

Time Period & Frequency The period and frequency are reciprocals of each other. and Thus, if you know one, you can easily find the other. Example If the period is 50 ms, the frequency is 0.02 MHz = 20 kHz.

Diode Models The characteristic curve for a diode can be approximated by various models of diode behavior. The model you will use depends on your requirements. IF The ideal model assumes the diode is either an open or closed switch. Forward bias VR VF 0.7 V The practical model includes the barrier voltage in the approximation. Reverse bias The complete model includes the forward resistance of the diode. IR

Half-wave Rectifier Rectifiers are circuits that convert ac to dc. Special diodes, called rectifier diodes, are designed to handle the higher current requirements in these circuits. The half-wave rectifier converts ac to pulsating dc by acting as a closed switch during the positive alteration. D + - RL D - + The diode acts as an open switch during the negative alteration. RL

Full-wave Rectifier The full-wave rectifier allows unidirectional current on both alterations of the input. The center-tapped full-wave rectifier uses two diodes and a center-tapped transformer. The ac on each side of the center-tap is ½ of the total secondary voltage. Only one diode will be biased on at a time. F D1 Vsec 2 Vsec 2 RL D2

Bridge Rectifier The bridge rectifier is a type of full-wave circuit that uses four diodes. The bridge rectifier does not require a center-tapped transformer. At any instant, two of the diodes are conducting and two are off. F D3 D1 RL D2 D4

Peak Inverse Voltage (PIV) Diodes must be able to withstand a reverse voltage when they are reverse biased. This is called the peak inverse voltage (PIV). The PIV depends on the type of rectifier circuit and the maximum secondary voltage.

Power Supplies By adding a filter and regulator to the basic rectifier, a basic power supply is formed. Typically, a large electrolytic capacitor is used as a filter before the regulator, with a smaller one following the regulator to complete filtering action. IC regulator F D3 D1 7805 D2 D4 C1 C2 1000 mF 1 mF

Special Purpose Diode Special purpose diodes include Zener diodes – used for establishing a reference voltage Varactor diodes – used as variable capacitors Light-emitting diodes – used in displays Photodiodes – used as light sensors

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