Half Wave Rectifier With filter
The half wave rectifier converts the Alternating Current (AC) into Direct Current (DC). But the obtained Direct Current (DC) at the output is not a pure Direct Current (DC). It is a pulsating Direct Current (DC).
The pulsating Direct Current (DC) is not constant. It fluctuates with respect to time. When this fluctuating Direct Current (DC) is applied to any electronic device, the device may not work properly. Sometimes the device may also be damaged. So the fluctuating Direct Current (DC) is not useful in most of the applications.
Therefore, we need a Direct Current (DC) that does not fluctuate with respect to time. The only solution for this is smoothing the fluctuating Direct Current (DC). This can be achieved by using a device called filter.
The pulsating Direct Current (DC) contains both AC and DC components. DC components are useful but AC components are not useful. So we need to reduce or completely remove the AC components. By using the filter, we can reduce the AC components at the output.
The filter is an electronic device that allows dc components and blocks the ac components of the rectifier output.
The filter is made up of a combination of components such as capacitors, resistors, and inductors. The capacitor allows the ac component and blocks the dc component. The inductor allows the dc component and blocks the ac component.
In this tutorial, a filter made up of a combination of resistor and capacitor is explained.
In the below circuit diagram, the capacitor C is connected in shunt with load resistor (RL).
When AC voltage is applied, during the positive half cycle, the diode D is forward biased and allows electric current through it.
As we already know that, the capacitor provides high resistive path to dc components (low-frequency signal) and low resistive path to ac components (high-frequency signal).
Electric current always prefers to flow through a low resistance path. So when the electric current reaches the filter, the dc components experience a high resistance from the capacitor and ac components experience a low resistance from the capacitor.
The dc components does not like to flow through the capacitor (high resistance path). So they find an alternative path (low resistance path) and flows to the load resistor (RL) through that path.
On the other hand, the ac components experience a low resistance from the capacitor. So the ac components easily passes through the capacitor. Only a small part of the ac components passes through the load resistor (RL) producing a small ripple voltage at the output.
The passage of ac components through the capacitor is nothing but charging of the capacitor.
In simple words, the ac components is nothing but an excess current that flows through the capacitor and charges it. This prevents any sudden change in the voltage at the output.
During the conduction period, the capacitor charges to the maximum value of the supply voltage. When the voltage between the plates of the capacitor is equal to the supply voltage, the capacitor is said to be fully charged.
When the capacitor is fully charged, it holds the charge until the input AC supply to the rectifier reaches the negative half cycle.
When the negative half cycle is reached, the diode D gets reverse biased and stops allowing electric current through it. During this non-conduction period, the input voltage is less than that of the capacitor voltage. So the capacitor discharges all the stored charges through the load resistor RL. This prevents the output load voltage from falling to zero.
The capacitor discharges until the input supply voltage is less than the capacitor voltage. When the input supply voltage is greater than the capacitor voltage, the capacitor again starts charging.
When the positive half cycle is reached again, the diode D is forward biased and allows electric current. This makes capacitor to charge again.
The capacitor filter with a large discharge time constant will produce a very smooth DC voltage.
Thus, a smooth and steady DC voltage is obtained by using the filter. "Keyword"
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