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Full wave rectification rectifies the negative component of the input voltage to a positive voltage, and then converts it into DC (pulse current) utilizing a diode bridge configuration. In contrast, half-wave rectification removes just the negative voltage component using a single diode before conve...

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Lab Report (CSE 7th Batch) Subject: Electrical Devices & Circuits Submitted By Lecturer : Maisha Maliha Dept Of CSE, CCNUST Submitted From Student Name : Saiful Islam Bhuiyan

ID: 111121013

Full-Wave Rectification and Half-Wave Rectification Rectification methods to convert AC (Alternating Current) to DC (Direct Current) include full-wave rectification and half-wave rectification. In both cases, rectification is performed by utilizing the characteristic that current flows only in the positive direction in a diode.

Full wave rectification rectifies the negative component of the input voltage to a positive voltage, and then converts it into DC (pulse current) utilizing a diode bridge configuration. In contrast, half-wave rectification removes just the negative voltage component using a single diode before converting to DC. Afterward, the waveform is smoothed by charging/discharging a capacitor, resulting in a clean DC signal. From this, it can be said that full-wave rectification is a more efficient method than half-wave rectification since the entire waveform is used. Also, a ripple voltage that appears after smoothing will vary depending on the capacitance of this capacitor and the load.Given the same capacitance and load, ripple voltage is smaller with full-wave rectification than haifwave rectification. Of course it goes without saying that the smaller the ripple voltage the better the stability.

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AC-DC Conversion Method: Transformer Method (AC-DC Converter)ACDC Conversion Method There is a transformer method and switching method for AC-DC conversion. Here we will cover the

Transformer Method: Shown here is the transformer circuit configuration of a typical AC-DC converter.

The figure below shows the transition of the voltage waveform using the transformer method. In the transformer method, the input AC voltage is first stepped down to an appropriate level using a transformer (e.g. 100VAC to 10VAC). This is AC-AC conversion, and the step-down voltage is set via the winding ratio of the transformer. Next, the stepped down AC voltage is full-wave rectified using a diode bridge rectifier and converted into pulsed DC. Finally, a capacitor is used to smooth the waveform, resulting in DC output with small ripple voltage. This is the most common way of performing AC-DC conversion.

【Waveform Transition (Transformer Method)】

Switching Method: Shown here is the switching circuit configuration of a typical AC-DC converter.

The figure below shows the transition of the voltage waveform using the switching method. Unlike the transformer method, which first performs step-down AC-AC in the transformer block, with the switching method the input AC voltage is first rectified as-is by the diode bridge circuit. In the case of general households, this input is normally between 100VAC and 200VAC, requiring a diode bridge that can handle large voltages. Next the DC waveform is smoothed using a capacitor. Similarly, a high-voltage capacitor is needed. Subsequently, this high DC voltage is chopped (separated) by turning ON/OFF the switching element, then transmitted to the secondary side via step-down operation using the high-frequency transformer. At this time, the chopped waveform becomes a square wave. The frequency of the switching element is higher than that used in households (i.e. 100 kHz vs. 50/60 kHz). Increasing the frequency allows the use of smaller, lighter transformers.

【Waveform Transition (Switching Method)】

Light load mode What is light load mode? Light load mode is a technology that improves efficiency at light loads (when the output current is small). In DC/DC converters and other devices, it is sometimes referred to as burst mode

Light load mode: Light load mode is a technology that improves efficiency at light loads (when the output current is small). In DC/DC converters and other devices, it is sometimes referred to as burst mode .Light load mode switching AC/DC and DC/DC converters supply a stable output voltage by performing chopping via ON/OFF switching then smoothing using a capacitor. However, momentary current leakage (through-current) is generated during ON/OFF switching. In other words, the more ON/OFF switching operations per unit time, the greater the loss due to leakage current and lower the efficiency. When the period is constant (PWM control) the number of switching operations per unit time is constant even if the ON/OFF time ratio changes. Consequently, the (self) power consumption is also constant, resulting in decreased efficiency due to loss caused by leakage current generated during switching at light loads. Therefore, at low current (light load) it is preferable to use PFM control which slows down and lengthens the period, reducing the number of ON/OFF switching’s per unit time in order to minimize loss. This technology is called light load mode.

[PWM and PFM Operation] Switching between PWM control featuring a constant period at heavy loads (large current) and PFM control that changes the period at light loads (low current) depending on the conditions makes it possible to further improve efficiency. ■ PWM (Pulse Width Modulation) A control method that produces the output equivalent from the input voltage at a constant frequency by turning the switch ON. ■ PFM (Pulse Frequency Modulation) A method for generating the equivalent output by changing the frequency (OFF time) while keeping the ON time constant. There is also a type that varies the ON time while keeping the OFF time constant....