# Full Wave Rectifier Circuit with Working Theory

If you know what is rectifier, then you may know the ways to reduce the ripple or voltage variations on a direct DC voltage by connecting capacitors across the load resistance. This method may be suitable for low power applications, but not for applications which need a steady and smooth DC supply. One method to improve on this is to use every half-cycle of the input voltage instead of every other half-cycle waveform. The circuit which allows us to do this is called a Full Wave Rectifier. Let’s see full wave rectifier theory in detail. Like the half wave circuit, working of Full Wave Rectifier circuit is an output voltage or current which is purely DC or has some specified DC voltage.

## Full Wave Rectifier Circuit with Working

Full wave rectifiers have some fundamental advantages over their half wave rectifier counterparts. The average (DC) output voltage is higher than for half wave rectifier, the output of the full wave rectifier has much less ripple than that of the half wave rectifier producing a smoother output waveform.

### Full Wave Rectifier Theory

In a full wave rectifier circuit we use two diodes, one for each half of the wave. A multiple winding transformer is used whose secondary winding is split equally into two halves with a common center tapped connection. Configuration results in each diode conducting in turn when its anode terminal is positive with respect to the transformer center point C produces an output during both half-cycles. Full rectifier advantages are flexible compared to that of half wave rectifier.

### Full Wave Rectifier Circuit

The full wave rectifier circuit consists of two power diodes connected to a single load resistance (RL) with each diode taking it in turn to supply current to the load resistor. When point A of the transformer is positive with respect to point A, diode D1 conducts in the forward direction as indicated by the arrows.When point B is positive in the negative half of the cycle with respect to C point, the diode D2 conducts in the forward direction and the current flowing through resistor R is in the same direction for both half-cycles of the wave.

The output voltage across the resistor R is the phasor sum of the two waveforms, it is also known as a bi-phase circuit.The spaces between each half-wave developed by each diode is now being filled in by the other. The average DC output voltage across the load resistor is now double that of the single half-wave rectifier circuit and is about 0.637Vmax of the peak voltage by assuming no losses. VMAX is the maximum peak value in one half of the secondary winding and VRMS is the rms value.

#### Working of Full Wave Rectifier

The peak voltage of the output waveform is the same as before for the half-wave rectifier provided each half of the transformer windings have the same rms voltage. To obtain a different DC voltage output different transformer ratios can be used. The disadvantage of this type of full wave rectifier circuit is that a larger transformer for a given power output is required with two separate but identical secondary windings makes this type of full wave rectifying circuit costly compared to the Full Wave Bridge Rectifier circuit.

Given Circuit gives a overview on working of full wave rectifier. A circuit that produces the same output waveform as the full wave rectifier circuit a is that of the Full Wave Bridge Rectifier. Single phase rectifier uses four individual rectifying diodes connected in a closed loop bridge configuration to produce the desired output wave. The advantage of this bridge circuit is that it does not require a special center tapped transformer, so it reduces its size and cost. Single secondary winding is connected to one side of the diode bridge network and the load to the other side.

The four diodes labelled D1 to D4 are arranged in series pairs with only two diodes conducting current during each half cycle duration. When the positive half cycle of the supply goes, D1, D2 diodes conduct in a series while diodes D3 and D4 are reverse biased and the current flows through the load. During the negative half cycle, D3 and D4 diodes conduct in a series and diodes D1 and D2 switch off as they are now reverse biased configuration.

Current flowing through the load is unidirectional mode and the voltage developed across the load is also unidirectional voltage, same as for the previous two diode full-wave rectifier model. Therefore the average DC voltage across the load is 0.637V.During each half cycle the current flows through two diodes instead of just one doide, so the amplitude of the output voltage is two voltage drops 1.4V less than the input VMAX amplitude, ripple frequency is now twice the supply frequency 100Hz for a 50Hz supply or 120Hz for a 60Hz supply.

#### Advantages of Full Wave Rectifier

you can use four individual power diodes to make a full wave bridge, readymade bridge rectifier components are available off-the-shelf in a range of different voltage and current sizes that can be soldered directly into a PCB circuit board or be connected by spade connectors.The full-wave bridge rectifier gives us a greater mean DC value with less superimposed ripple while the output waveform is twice that of the frequency of the input supply. Therefore increase its average DC output level even higher by connecting a suitable smoothing capacitor across the output of the bridge circuit.

The advantages of a full-wave bridge rectifier is that it has a smaller AC ripple value for a given load and a smaller reservoir or smoothing capacitor than an equivalent half-wave rectifier circuit. The fundamental frequency of the ripple voltage is twice that of the AC supply frequency 100Hz where for the half-wave rectifier it is exactly equal to the supply frequency 50Hz.The amount of ripple voltage that is superimposed on top of the DC supply voltage by the diodes can be virtually eliminated by adding a much improved π-filter to the output terminals of the bridge. Low-pass filter consists of two smoothing capacitors of the same value and a choke or inductance across them to introduce a high impedance path to the alternating ripple component.

Alternative is to use an off the shelf 3terminal voltage regulator IC, such as a LM78xx where “xx” stands for the output voltage rating for a positive output voltage or its inverse equivalent the LM79xx for a negative output voltage which can reduce the ripple by more than 70dB Datasheet while delivering a constant output current of over 1 amp.

It is the basic component to get D.C voltage for the components which operates with D.C voltage. One can describe its working as a full wave rectifier project.

It is the heart of the circuit. Full wave rectifier uses the diode bridge. Capacitors are used to get rid of ripples. Based on the requirement of D.C voltage

**Photo Credits:**

- Full wave rectifier by dlnmh9ip6v2uc.cloudfront
- Full wave rectifier output by daenotes
- Full Wave Rectifier Theory by i.stack.imgur
- Working of Full Wave Rectifier by radio-electronics
- Full Wave Rectifier IC by otenko