Rectification, is the term used to describe the conversion of voltages or current.
Rectifier, diodes used in a circuit to convert AC to DC voltage or current.
2.) Types of Rectifier Circuits
- Full-wave Rectifier
- Full-wave Bridge Rectifier
3.) Operation of Full-wave Rectifier
The circuit shown below is a full-wave rectifier circuit.
In a full-wave rectifier circuit, a diode rectifier is placed in series with each half of the center-tapped transformer secondary winding and the load. Effectively this circuit has 2 half-wave rectifiers working into the same load.
During the first half cycle, when point A of the transformer is positive:
- It makes the diode D1 anode positive so that it can conduct current.
- Current will flow from A through diode D1 to point C through the load resistor to point D and then to ground at the transformer center-tapped terminal.
- A positive voltage will be developed across the load resistor.
During the next half cycle when point B of the transformer is positive:
- It makes the diode D2 anode positive so that it will conduct.
- Current will flow from B through the diode D2 to point C, though the load resistor to point D and then earth, the center-tapped of the transformer.
- This current flow will also develop another positive voltage across the load resistor.
Since both pulses of the current flowing through the load are in the same direction, a pulsating dc voltage now appears across the load. The full-wave rectifier has changed both halves of the ac input voltage to a pulsating dc output voltage. The sequence half cycles of the input ac voltage will be rectified in the same way. The output voltage develop across the load resistor will be shown in the figure below:
The disadvantage of the full-wave rectifier is that it requires a center-tapped transformer. It becomes costly and heavier in weight.
4.) Operation of Full-wave Bridge Rectifier
The circuit shown in figure below is a full-wave bridge rectifier that requires a non-center-tapped transformer and 4 diodes. At any one time 2 diode will be in operation.
During the positive half cycle, when point A is positive.
- The diodes D2 and D4 anodes will be positive, while the remaining 2 diodes will be negative.
- Current will flow from point A via D2 to point C, through the load resistor to point D, through diode D4 to point B, through the trransformer and back to point A.
- This current flow will developed a positive voltage across the load resistor.
During the next half cycle, point B is positive,
- The diode D1 and Diode D3 anode will be positive, while the remaining 2 diode will be negative.
- Current will flow via diode D3 to point C, through the load resistor to point D, through diode D1 and back to point B.
- This current will also develop a positive voltage across the load resistor.
The full-wave bridge rectifier has the advantage of using a non center-tapped transformer.As a result the rectifier circuit become lighter in weight. Since diode are inexpensive, the full wave bridge rectifier is commonly used in modern solid-state electronic equipment. In many cases, a special package of 4 diodes are available to aboid the extra wiring required in this circuit.
5.) RC Filter Circuit
Figure below shows an RC filter circuit.
- Consisting of 2 capacitors C1 and C2 and resistor R.
- The capacitor C1 is called reservoir capacitor.
- The capacitor C2 is called smoothing capacitor.
- The resistor R is called Dropper resistor.
When point X in figure above received the positive peak voltage Vp at the rectifier output, correspond to point T1 in figure below, the capacitor C1 will be charged up to its peak value.
When the rectifier reduces its output voltage from its peak value to zero, the capacitor C1 start to discharge its energy. The time taken for the rectifier output voltage to reach its peak value is faster than the time taken for the capacitor C1 to discharge.
The reservoir capacitor still remain at certain amount of energy (voltage) when the rectified voltage reaches zero, correspond to point T2 as shown below.
The next positive puls will charge up capacitor C1 to its peak voltage again. The process of charging and discharging across C1 will continue in the subsequent positive pulses.
Since C1 does not discharge to zero, the load resistor will continue to be supplied with electrical energy from the capacitor C1. As a result the voltage develop across the resistor will contain an AC ripple as shown below.
The resistor R will reduce the ripple further as shown below.
The capacitor C2 will now received these ripple voltage. The charging and discharging action of C2 will further reduce the ripple to a very small percentage. The voltage across the load restor will be almost a pure DC voltage as shown below.
7.) Resistor Inductor (RL) Filter Circuit
It is similar in its circuit and its operations to that of the rc filter except that an iron cored choked is used instead of resistor.
The choke give a better filtering because of its high Inductive Reactance. It also prove high resistance to AC but low resistance to DC. Hence, this is good for filtering AC ripple.
Thanks for this, this will really help me out with my resistor project.
ReplyDeleteGlad that I could help.
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