The full wave rectifier can be constructed in two ways. One is center tapped full wave rectifier consisting of two diodes and one center tapped secondary winding transformer and the second is a Bridge Rectifier consisting of four diodes namely D1, D2, D3, D4 connected.
The bridge rectifier is constructed by using 4 diodes in the form of a Wheatstone bridge which is fed by a step-down transformer. When a step downed AC supply fed through the bridge, it is seen that during the positive half cycle of secondary supply the diodes D1 and D3 Shown in below figure are in forward biased.
So the current will pass through the diode D1, load R , and diode D3. And vice versa during the negative half cycle of secondary input. Generally, an AC input is in the form of the sinusoidal waveform sin wt. The output waveform and circuit diagram is shown below.
The center tapped full wave rectifier is build with a center tapped transformer and two diodes D1 and D2, are connected as shown in below figure. When the AC power supply switched ON, the voltage appearing across the terminals AB of transformer secondary terminal side.
So the current will pass through the diode D1 and Load R. During the negative cycle of the secondary cycle, only the diode D2 will conduct and current will pass through the diode D2 and the Load R. A bridge rectifier does not require a bulky center tapped transformer, nowadays the center tapped transformers are costlier than diodes and a step-down transformer hence reduced size and cost.
The PIV peak inverse voltage ratings of the diodes in bridge rectifier is half than that of needed in a center tapped full wave rectifiers. The diode used in bridge rectifier has capable of bearing high peak inverse voltage. Whereas in center tapped rectifiers, the peak inverse voltage coming across each diode is double the maximum voltage across the half of the secondary winding.
The transformer utilization factor TUF also more in bridge rectifier as compared to the center tapped full wave rectifier, Which makes it more advantageous. PIV: For rectifiers, Peak inverse voltage PIV or peak reverse voltage PRV can be defined as the maximum value of the reverse voltage of a diode, which occurs at the peak of the input cycle when the diode is in reverse bias. Using four diodes the bridge rectifier the circuit has a distinctive format with the circuit diagram based on a square with one diode on each leg.
In view of its performance and capabilities, the full wave bridge rectifier is used in many linear power supplies, switch mode power supplies and other electronic circuits where rectification is needed. A diagram of the basic bridge rectifier circuit has a bridge rectifier block at the centre.
This consists of a bridge circuit which includes four diodes. These can be individual diodes, or it is also easy to obtain bridge rectifiers as a single electronic component.
The bridge rectifier provides full wave rectification and has the advantage over the full wave rectifier using two diodes that no centre tap is required in the transformer. This means that a single winding is used for both halves of the cycle. Wound electronic components are expensive and including a centre tap means that two identical windings, each providing the full voltage are needed to provide the full wave rectification. This doubles the number of turns and increases the cost of the transformer.
This can be particularly important when designing linear power supplies or other electronic devices. To see how the bridge diode full wave rectifier operates it is useful to see the current flow over a compete cycle of the incoming waveform. Full wave bridge rectifier showing current flow In most power supply applications, whether for linear voltage regulators, or for switch ode power supply applications, the output from a bridge rectifier will be connected to a smoothing capacitor as part of the load.
These electronic components accept charge during the high voltage parts of the waveform and then give out charge to the load as the voltage falls. In this way they provide a more constant voltage than the direct output from the bridge rectifier.
This allows other circuits like the linear voltage regulators and switch mode power supplies to operate correctly. Capacitors are used within many power supply applications for both linear voltage regulators and switch mode power supplies to smooth the rectified waveform which would otherwise vary between the peak waveform voltage and zero.
By smoothing the waveform, it is possible to run electronic circuits from it. Read more about Capacitor Smoothing. In terms of the bridge rectifier and its diodes, the inclusion of the capacitor means that the current taken through the diodes will have significant peaks as the capacitor charges up. When selecting the electronic components for the bridge rectifier, it is necessary to ensure that they can accommodate the peak current levels. The bridge rectifier components can come in a variety of forms.
They can be made using discrete diodes. A ring of the four diodes can easily be made either on a tag or as part of a printed circuit board. Care must be taken to ensure that the diodes are sufficiently ventilated as they can dissipate heat under load.
Alternatively bridge rectifiers come as single electronic components containing the four diodes in a single block or encapsulation. Some of these bridge rectifiers are intended for mounting on a printed circuit board and may have wires for through hole mounting. Others may be surface mount devices. Some bridge rectifiers are contained in larger encapsulations and are intended for mounting on a heat sink.
As these rectifiers are designed to carry significant levels of current, they can dissipate significant levels of heat as a result of the diode drop and also the internal resistance of the bulk silicon used for the diodes.
There are several points that need to be considered when using a bridge rectifier to provide a DC output from an AC input:. Calculate heat dissipated in the rectifier: The diodes will drop the voltage by a minimum of 1. It results from the standard voltage drop across the diode and also the resistance within the diode. Note that the current passes through two diodes within the bridge for any half cycle.
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