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Full wave rectifier with capacitor filter

January 15, 20249 min read

Rectifier circuit consists of diodes which convert AC power supply into DC power supply and this circuit is useful for devices which run on DC power supply. It is quite difficult to provide a direct DC supply to devices that require a direct power source, as most power generation and transmission is based on AC. Adding a capacitor to a full wave rectifier can further filter out noise or ripples in the output. Capacitors are charge storage devices that absorb transients in circuits improving the quality of the output signal.

framework:

A capacitor as a filter
full wave rectifier

center tapped and bridge rectifier difference
conclusion

A capacitor as a filter

A capacitor is a reactive device whose response varies depending on the applied frequency, and this means that the effect of the capacitor on the signal will depend on the frequency. Since the filter covers a wide range of frequencies, capacitors are used on the filter. Furthermore, capacitors are passive components as they do not require energy to operate and thus are used in passive filter circuits.

Generally, a capacitor becomes an open circuit when it is fully charged and generally the reactance at higher frequency is less, hence the capacitor acts as a short circuit and thus passes the higher frequency. Allows to do. On the other hand, when the frequency is low the reactance of the capacitor is high making it difficult to pass the low frequency. Most of the time the frequency of ripples and other transients is quite low, so the capacitor blocks them.

full wave rectifier

As mentioned above, rectifier is a circuit which converts AC supply into DC with the help of diodes. The circuit for rectification can be designed in two ways, one by using two diodes and the other by making a bridge of four diodes.

Center Tapped Full Wave Rectifier

A full wave rectifier circuit with two diodes requires a transformer, so here is the circuit for a full wave rectifier circuit with two diodes:

The diodes are connected across the load R.l And when point A has positive polarity with respect to point C, diode D1 Will behave as per further prejudice. However, when point B is at positive potential with respect to point C then diode D2 Allows the flow of current, and this is how a full wave rectifier works. As a result of this behavior, the negative half of the AC supply is cut off, and a pure DC waveform is produced at the output.

In other words, the first diode operates in the positive half cycle of the AC supply and the second diode is in the reverse bias state. Whereas in the negative half cycle, the second diode conducts and the first remains reverse biased.

Full wave rectifier with capacitor filter

The DC output obtained from a full wave rectifier still contains some ripple which affects the signal quality. Therefore, to filter these ripples a capacitor is usually used which is connected in parallel to the connected load. Now the power supply is turned on and the capacitor starts charging when the diode D1 is in forward bias which is in the positive half cycle. In the negative half cycle, the capacitor begins to discharge but is not completely discharged.

The output of the rectifier has both AC and DC components and as we know capacitors prevent direct current. So, all the AC components at the rectifier output will pass through the capacitors, leaving a pure DC signal to the load:


The final waveform for the rectifier output with capacitor will be:

full wave bridge rectifier

Full wave bridge rectifier consists of four diodes arranged in the form of a bridge. However, it does not require a center tap transformer which makes it less expensive than other types. The output of the bridge rectifier is almost the same as that of the centre-tapped full-wave rectifier, the circuit of the full-wave bridge rectifier is given below:

Here the diodes are in series with each other, and both diodes will conduct during every half cycle, diode D in the positive half cycle.1 and d2 The forward one will be biased, and the other two will be in the non-conducting state. However, in the negative half cycle, the other two diodes D3 and d4 Will be in further bias.

Full-wave bridge rectifiers have a higher voltage drop than center-tapped transformer full-wave rectifiers because there are two diodes in the conducting state for each cycle. Furthermore, the peak inverse voltage of the bridge rectifier is equal to the voltage in the transformer on the secondary side, and thus it can be used in high-voltage applications. Since the functioning of both types of rectifier circuits is similar, the output waveform will be the same.

Bridge rectifier with capacitor filter

Center-Taped Transformer Like the full wave rectifier, the capacitor in the bridge rectifier is connected in parallel to the load. This capacitor is also known as a smoothing capacitor, because it blocks DC and allows the AC component of the signal to pass through it:


The function of the capacitor filter in a bridge rectifier is similar to that of a centre-tap full-wave rectifier, and the ripple factor is the same for both types. Therefore, the waveform will be the same after connecting the smoothing capacitor to the bridge rectifier. It should be noted that if we select a capacitor with higher capacitance the ripple factor further reduces but the discharge voltage will increase.

Difference between center tapped full wave rectifier and bridge rectifier

Although both the circuits work in the same way and give similar outputs, there are some minor differences between the two:

Rectifier Parameters bridge rectifier center tap full wave rectifier
peak inverse voltage PIV=VM PIV=2VM
transformer utilization factor 0.812 0.693
voltage drop across diode High Less
center harness not necessary Necessary
transformer kva rating Less High
wave factor 0.48 0.48

conclusion

Capacitors are charge storage passive devices used for a variety of applications, one of which is to filter any transients at the output of a circuit. In rectifier circuits, capacitors are used to filter the ripples at their outputs which are in essence AC components. Since capacitors always block DC, it will only allow the AC component to pass through it which will then go to ground.

Full wave rectifiers are divided into two types, one with a center-tap transformer while the other has a bridge of four diodes. So, the behavior of capacitors with both full wave rectifier circuits will be the same.

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