Center Tapped Full Wave Rectifier : Working, Circuit diagram, Characteristics & Its Applications

An electrical device that is used for converting alternating current (AC) to direct current (DC) is called a rectifier. Generally, these are available in two types half wave rectifier or HWR and full wave rectifier or FWR. HWRs are not appropriate where a stable, as well as flat DC voltage, is necessary. So HWR is not capable of converting AC-DC. To overcome this main drawback, a full wave rectifier (FWR) is used. This kind of rectifier has benefits as compared to HWR. The normal DC o/p voltage generated by the FWR is higher as compared to HWR. Again FWRs are categorized into two types center tapped full wave rectifier & bridge full wave rectifier. This article discusses an overview of a center-tapped full wave rectifier – working with applications.

What is Center Tapped Full Wave Rectifier?

A type of rectifier which is designed by using two diodes as well as a center tapped transformer for converting the whole AC signal to DC is called center tapped FWR.  This is called as “full wave center tapped” because there are two full cycles in one complete cycle of AC voltage. This means that it produces twice as much DC voltage as a half-wave rectifier would produce from an equivalent AC source.

Centre Tap Full Wave Rectifier Circuit

The circuit diagram of the center tap full wave rectifier circuit is shown below. This rectifier circuit can be designed with an AC source, two diodes, a load resistor & a center tapped transformer. As shown in the following circuit diagram, the two diodes are connected to the two ends of a center-tapped transformer.

The AC source within the circuit is given to the center-tapped transformer’s main winding. A center tap or extra wire which is connected at the center of the secondary (minor) winding will divide the i/p voltage into 2 parts.

The secondary winding’s higher portion is coupled to the ‘D1’ diode whereas the lower portion is coupled to the ‘D2’ diode. Both the diodes are simply connected to a load resistor (RL) using a center tapped transformer. Usually, the center tap is considered as the ground point or zero voltage reference.

How Does a Center-Tapped Full-Wave Rectifier Works?

The operation of the center tapped full wave rectifier is, once i/p voltage (Vin) is applied to the rectifier, then the center-tapped transformer’s secondary winding will divide this applied voltage into 2 parts positive & negative.

Throughout the +ve half i/p voltage cycle, the ‘A’ end turns into positive & ‘B’ end turns into negative. Therefore, the D1 diode will become forward biased & D2 diode will become reverse biased. These two D1 and D2 diodes will conduct at the same time. So, once the D1 diode conducts, then the D2 diode will not conduct. Whenever the ‘D1’ diode is conducting, the flow of current ‘I’ will be throughout this diode D1 and load resistor ‘RL’.

Throughout the -ve half-cycle of the i/p voltage, the ‘B’ end will become positive whereas the ‘A’ end will become negative to make the ‘D2’ diode forward biased & ‘D1’ diode reverse biased. The flow of current throughout the load resistor ‘RL’ is in a similar direction throughout both the +ve & the -ve half cycle of the applied i/p voltage. Therefore, the DC o/p voltage like Vout = i RL can be obtained across the RL

The waveforms for the applied input voltage, the flow of current throughout the load & the o/p voltage obtained across the load. The center tapped full wave rectifier waveforms are shown below.

Please refer to this link to know more about: the Center Tapped Full Wave Rectifier with Capacitor Filter.

Difference between Center Tapped Full Wave Rectifier Vs Bridge Rectifier

The difference between center tapped full wave rectifier and bridge rectifier includes the following.

 Center Tapped Full Wave Rectifier Bridge Rectifier In center tapped FWR, two diodes are used. In the bridge rectifier, four diodes are used. Its Peak inverse voltage (PIV) is 2 Vs max. Its Peak inverse voltage (PIV) is Vs max. The transformer is used for center tapping. The transformer is not required. The voltage drop is less across the diode. The voltage drop is high because of the four diodes. The TUF (transformer utilization factor) is 0.691 The TUF (transformer utilization factor) is 0.814 Its voltage regulation is better. Its voltage regulation is good. It has less circuit complexity. It has more circuit complexity. These rectifiers are not economical as compared to the bridge rectifier. These rectifiers are economical.

Characteristics

The characteristics of the center tapped full wave rectifier include ripple factor, rectifier efficiency, PIV, DC o/p current, DC o/p voltage, RMS, VRMS, and form factor.

Efficiency

The efficiency of this rectifier specifies how the rectifier efficiently changes from AC to DC. Once the rectifier efficiency is high then the rectifier is said to be good whereas if the rectifier efficiency is low then the rectifier is said to be inefficient.

So, the efficiency of the rectifier is the ratio of direct current (DC) o/p power & the AC i/p power which is written like the following.

η = output PDC / input PAC

The efficiency of a center-tapped FWR is approximately 81.2%.

As compared to HWR, the FWR efficiency is double. So this rectifier is very efficient.

Ripple Factor (RF)

The RF or ripple factor is very helpful in measuring the ripples available within the output DC signal. Once the ripple factor (R.F) is high then it specifies a maximum pulsating DC signal whereas if a ripple factor (R.F) is low then it specifies a minimum pulsating DC signal. The ripple factor (RF) is the ratio of the ripple voltage and the clean DC voltage. This can be measured by using the following formula.

γ = √ (Vrms/VDC)2 -1

Peak Inverse Voltage or PIV

The term PIV stands for “Peak inverse voltage” which is the highest voltage one diode can resist within the condition of reverse bias. Once the voltage applied is higher as compared to the PIV, then the diode in the circuit will be damaged permanently.

The PIV or peak inverse voltage of center tapped full wave rectifier is 2Vsmax

DC O/P Current

When the flow of current throughout both the diodes like D1 & D2 is in a similar direction at the o/p load resistor (RL) then the o/p flow of current is the amount of D1 & D2 currents. So the flow of current generated from the D1 diode is Imax / π & the current generated from the D2 diode is Imax /π.

So the o/p current IDC = 2Imax / π.

Here, ‘Imax’ is the max DC load current

DC O/P Voltage

The DC o/p voltage which is available at the ‘RL’ can be given as

VDC = 2Vmax /3.14

Where ‘Vmax’ is the max secondary voltage

VRMS

The RMS value ‘VRMS’ is the o/p load voltage. So the VRMS for a center tapped full wave rectifier is VRMS = IRMS RL => (Im/√2) RL

IRMS

‘IRMS’ is the root mean square value for the load current. So the RMS value of load current is

IRMS = Im/√2

Form factor (F.F)

Form factor (FF) is the ratio of the value of RMS for current & the DC o/p current. So mathematically it can be written as

Form Factor = The value of RMS for current/DC o/p current

For a center tapped FWR, the F.F (form factor) value is 1.11.

Advantages and Disadvantages

The advantages of center-tapped FWR include the following.

High efficiency & outputs are high because an AC supply provides power throughout both half cycles.

• Less power loss.
• Less ripple factor as compared to HWR.
• The DC load current & DC o/p voltage are double as compared to HWR.
• The rectification efficiency is double as compared to a half-wave rectifier.

The center tapped full wave rectifier disadvantages include the following.

• These are expensive.
• Every diode uses simply one-half of the supply voltage which is developed within the secondary of the transformer; thus the obtained DC o/p is small.
• For the tapping, it is not easy to place the center on the secondary.
• The diode utilized in the circuit should be capable of bearing high PIV (peak inverse voltage) as PIV coming across every diode is double the highest voltage across the half of the minor winding.

Applications

The applications of center-tapped FWR include the following.

• This rectifier is used to convert high input AC voltage to low DC voltage.
• These types of rectifiers are used as basic components within the power supply units due to their high efficiency.
• These are used to provide power to motors, LEDs, etc.

Thus, center tapped FWR is one kind of full wave rectifier that makes unidirectional current flow through the load in the complete input voltage cycle. This rectifier uses two diodes which are connected across the center-tapped transformer’s terminals. So once one diode conducts mainly for +ve half cycle then another diode will conduct for a -ve half cycle of the input supply. Consequently, a unidirectional current flow is maintained throughout the load resistance. Here is a question for you, what is the purpose of a center tapped transformer?