Bridge rectifier; types and applications

The rectifier circuit is a type of power Electronics circuit which is used to convert AC (Alternating Current) into DC (Direct Current).

Rectifiers are mainly classified into three types namely half-wave, full-wave, and bridge rectifier. The main function of all these rectifiers is the same as the conversion of current but they do not efficiently convert the current from AC to DC. The center tapped full wave rectifier as well as bridge rectifier converts efficiently. 

A bridge rectifier circuit is a common part of the electronic power supplies. Many electronic circuits require a rectified DC power supply for powering the various electronic basic components from available AC mains supply. We can find this rectifier in a wide variety of electronic AC power devices like home appliances, motor controllers, modulation process, welding applications, etc. This article discusses an overview of a bridge rectifier and its working.

What is a Bridge Rectifier? 

A Bridge rectifier is an Alternating Current (AC) to Direct Current (DC) converter that rectifies mains AC input to DC output. Bridge Rectifiers are widely used in power supplies that provide necessary DC voltage for the electronic components or devices.

They can be constructed with four or more diodes or any other controlled solid-state switches. Bridge Rectifier Depending on the load current requirements, a proper bridge rectifier is selected. Components’ ratings and specifications, breakdown voltage, temperature ranges, transient current rating, forward current rating, mounting requirements, and other considerations are taken into account while selecting a rectifier power supply for an appropriate electronic circuit’s application.

Construction The bridge rectifier construction is shown below. This circuit can be designed with four diodes namely D1, D2, D3 & D4 along with a load resistor (RL). The connection of these diodes can be done in a closed-loop pattern to convert the AC (alternating current) to DC (Direct Current) efficiently. The main benefit of this design is the lack of an exclusive center-tapped transformer. So, the size, as well as cost, will be reduced. Once the input signal is applied across the two terminals like A & B then the o/p DC signal can be attained across the RL. Here load resistor is connected in between two terminals like C & D. The arrangement of two diodes can be made in such a way that the electricity will be conducted by two diodes throughout every half cycle. 

The pairs of diodes like D1& D3 will conduct electric current throughout the positive half cycle. Similarly, D2 & D4 diodes will conduct electric current throughout a negative half cycle.

 Bridge Rectifier Circuit Diagram

The main advantage of the bridge rectifier is that it produces almost double the output voltage as with the case of a full-wave rectifier using a center-tapped transformer. But this circuit doesn’t need a center-tapped transformer so it resembles a low-cost rectifier. The bridge rectifier circuit diagram consists of various stages of devices like a transformer, Diode Bridge, filtering, and regulators. Generally, all these blocks combination is called a regulated DC power supply that powers various electronic appliances. The first stage of the circuit is a transformer which is a step-down type that changes the amplitude of the input voltage. Most of the electronic projects use a 230/12V transformer to step-down the AC mains 230V to 12V AC supply. Bridge Rectifier Circuit Diagram The next stage is a diode-bridge rectifier which uses four or more diodes depending on the type of bridge rectifier. Choosing a particular diode or any other switching device for a corresponding rectifier needs some considerations of the device like Peak Inverse Voltage (PIV), forward current If, voltage ratings, etc. It is responsible for producing unidirectional or DC current at the load by conducting a set of diodes for every half cycle of the input signal. Since the output after the diode bridge rectifiers is of pulsating nature, and for producing it as a pure DC, filtering is necessary.

Filtering is normally performed with one or more capacitors attached across the load, as you can observe in the below figure wherein smoothing of the wave is performed. This capacitor rating also depends on the output voltage. The last stage of this regulated DC supply is a voltage regulator that maintains the output voltage to a constant level. Suppose the microcontroller works at 5V DC, but the output after the bridge rectifier is around 16V, so to reduce this voltage, and to maintain a constant level no matter voltage changes in the input side  a voltage regulator is necessary.

Bridge Rectifier Operation As we discussed above, a single-phase bridge rectifier consists of four diodes and this configuration is connected across the load. For understanding the bridge rectifier’s working principle, we have to consider the below circuit for demonstration purposes. During the Positive half cycle of the input AC waveform diodes, D1 and D2 are forward biased and D3 and D4 are reverse biased. When the voltage, more than the threshold level of the diodes D1 and D2, starts conducting, the load current starts flowing through it, as shown in the path of the red line in the diagram below.

Circuit Operation During the negative half cycle of the input AC waveform, the diodes D3 and D4 are forward biased, and D1 and D2 are reverse biased. Load current starts flowing through the D3 and D4 diodes when these diodes start conducting as shown in the figure. We can observe that in both cases, the load current direction is the same, i.e., up to down as shown in the figure – so unidirectional, which means DC current. Thus, by the usage of a bridge rectifier, the input AC current is converted into a DC current. The output at the load with this bridge wave rectifier is pulsating in nature, but producing a pure DC requires an additional filter like a capacitor. The same operation is applicable for different bridge rectifiers, but in the case of controlled rectifiers thyristors triggering is necessary to drive the current to load. 

Types of Bridge Rectifiers.

Bride rectifiers are classified into several types based on these factors: type of supply, controlling capability, bride circuit configurations, etc. Bridge rectifiers are mainly classified into single and three-phase rectifiers. Both these types are further classified into uncontrolled, half controlled, and full controlled rectifiers. Some of these types of rectifiers are described below. Single Phase and Three Phase Rectifiers The nature of supply, i.e., a single-phase or three-phase supply decides these rectifiers. The Single phase bridge rectifier consists of four diodes for converting AC into DC, whereas a three-phase rectifier uses six diodes, as shown in the figure. 

These can be again uncontrolled or controlled rectifiers depending on the circuit components such as diodes, thyristors, and so on. Single Phase and Three Phase Rectifiers Uncontrolled Bridge Rectifiers This bridge rectifier uses diodes for rectifying the input as shown in the figure. Since the diode is a unidirectional device that allows the current flow in one direction only. With this configuration of diodes in the rectifier, it doesn’t allow the power to vary depending on the load requirement. So this type of rectifier is used in constant or fixed power supplies. 

Uncontrolled Bridge Rectifiers Controlled Bridge Rectifier In this type of rectifier, AC/DC converter or rectifier – instead of uncontrolled diodes, controlled solid-state devices like SCR’s, MOSFET’s, IGBT’s, etc. are used to vary the output power at different voltages. By triggering these devices at various instants, the output power at the load is appropriately changed.

Controlled Bridge Rectifier Bridge Rectifier IC.

 The bridge rectifier like RB-156 IC pin configuration is discussed below. Pin-1 (Phase / Line): This is an AC input pin, where the connection of phase wire can be done from the AC supply toward this phase pin. Pin-2 (Neutral): This is the AC Input pin where the connection of the neutral wire can be done from the AC supply to this neutral pin. Pin-3 (Positive): This is the DC output pin where the positive DC voltage of the rectifier is obtained from this positive pin Pin-4 (Negative /Ground): This is the DC output pin where the ground voltage of the rectifier is obtained from this negative pin Specifications The sub categories of this RB-15 Bridge rectifier range from RB15 to RB158. Out of these rectifiers, the RB156 is the most frequently used one. The specifications of the RB-156 bridge rectifier include the following. O/p DC current is