What is a Controlled Rectifier?

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Editorial Team - everything PE

Sep 19, 2021

controlled rectifier is a type of AC to DC converter that provides adjustable DC output voltage from the given AC input supply. A controlled rectifier usually consists of an input filter capacitor, power electronics switches such as MOSFET/IGBT/BJT, inductor, diode, a high-frequency transformer(in an isolated configuration only, for isolation), and control circuits to provide regulated DC output. These rectifiers are ideal for applications such as medical instrumentation, commercial and industrial electronic equipment, electric power, and smart homes.

Controlled rectifiers are further classified into two configurations: Isolated and Non-isolated.

  • An isolated controlled rectifier uses a high-frequency transformer (flyback transformer or normal transformer) to establish galvanic isolation between the input AC supply and output DC circuit. This isolation provides several benefits such as ensuring the safety of human and sensitive devices from the high and potentially hazardous AC input voltage, breaking ground loops (helpful to isolate the noisy circuits from sensitive circuits), and avoiding floating output. The isolated uncontrolled rectifier employs various switching power supply topologies such as a Flyback converter, Forward converter, push-pull converter, bridge SMPS, isolated cuk, ringing choke converter, and resonant LLC converter.
  • A non-isolated controlled rectifier doesn’t need a transformer for operation. The input AC and output DC circuits share the common ground, and current can flow between them. Because of the absence of a transformer, these rectifiers have several advantages such as low cost, small size, high efficiency, and regulation. They can operate at a higher switching frequency which further reduces the size of passive components (inductors and capacitors). The non-isolated uncontrolled rectifier employs various switching power supply topologies such as a step-down/buck converter, step-up/boost converter, buck-boost converter, cuk converter, split-pi converter, zeta converter, and SEPIC converter.