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How Do Bridge Rectifiers Work?

Power supply units employ various circuit-level components to achieve a desired output. Such elements may include resistors, transistors, capacitors, diodes, or any combination of the above. More often, in complex power supply units, specialty devices must be implemented to perform a task. One such device that plays an integral role in the conversion of alternating current to direct current is the bridge rectifier circuit. This component, which has been used with regular frequency since its invention in the late 1800s, remains a staple in many power supply units of the modern era. In this blog, we will discuss everything you need to know about bridge rectifier circuits, including their design, operating principle, and variants.

When plugging a device into an outlet at a residential or commercial establishment, the result is receiving a single-phase alternating current. Power is transmitted as such because it is more economical and safe than direct current. However, many smaller appliances and devices call for a direct current with constant voltage for their power supply. Therefore, a bridge rectifier circuit must be in place between an AC power supply and the DC-requiring output device.

The simplest type of bridge rectifier is the single-phase rectifier, consisting of four diodes and a conduction pathway connecting each to the load. With this configuration, only two diodes conduct power for every half cycle, positive or negative. As a result, the output will always have the same polarity regardless of the input signal. A rectifier’s efficiency may be determined by taking a ratio of Pdc/Pac, where P represents power delivered. Pdc, in particular, may be further derived from Idc^2 * RL, where Idc= Imax/pi and Rl represents the reactive load. Since there is always some power lost in transition, the calculated maximum efficiency of a bridge rectifier is around 81%.

Although single-phase bridge rectifiers are the most common, it is important to be aware of other variants. Three-phase bridge rectifiers employ six diodes to achieve AC conversion, and they provide a high transformer-utilization factor for high-voltage applications. Capable of handling a three-phase alternating current power supply, these rectifiers provide less ripple than what is commonly found with a single-phase model. It is important to note that the output of the described rectifiers is constant and dependent on the input AC. Rectifiers that produce a fixed voltage are considered uncontrolled. On the other hand, some applications may demand a varying output voltage, in which case a controlled rectifier is needed. Controlled rectifiers incorporate thyristors which modify the phase angle and, therefore, the voltage output. Although thyristors are most commonly chosen as a control mechanism, devices may also rely upon MOSFETs, SCRs, or IGBTs.

Due to their low cost and reliable performance, bridge rectifiers are used extensively in applications requiring AC to DC conversions. However, rectifier components may also be used to produce different outputs. Most notably, bridge rectifiers can be used to detect the amplitude of a radio signal by acting linearly in response to the signal. They are also used to provide polarized voltage in the case of welding.

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