Page 324 - CITS - Electronic Mechanic - TT - 2024

ELECTRONICS MECHANIC - CITS

MODULE 20 : 3-Phase rectifier controlled &

uncontrolled d

LESSON 199 - 204 : 3-Phase Rectifier controlled &

uncontrolled

Objectives

At the end of this lesson you shall be able to
• state working principle of controlled & uncontrolled rectifiers
• state the applications of controlled & uncontrolled rectifiers
High current rectifiers

In high current rectifier SCRs are mainly used in devices where the control of high power, possibly at high voltage,
is needed. The ability to switch large currents on and off makes the SCR suitable for use in medium to high-
voltage AC power control applications, such as lamp dimming, regulators and motor control.
High Current Rectifiers are used in a variety of industrial applications such as Electroplating, Electro coloring,
Magnetization, Hydrogenation, Electro winning, Capacitor Film Formation, Cathode Protection, Anodizing, ED
Coating (Painting), Chlorination, Water Treatment, Battery Formation, Electro heating.
Difference between uncontrolled and controlled rectifierts

Controlled rectifiers
A controlled rectifier can control the power fed to the load. It is used to convert AC supply into unidirectional DC
supply in an inverter. Controlled rectification is the process of converting AC to direct current (DC) based on the
required voltage and current demand. To design the controlled feature, The silicon-controlled rectifier (SCR) is
basically a thyristor, a four-layer (P–N–P–N) semiconductor device.

Uncontrolled rectifiers
An uncontrolled rectifier is a type of AC to DC converter that provides fixed DC output voltage from a given AC
input supply. These rectifiers are used in applications where fixed DC voltage is essential.

Silicon Controlled Rectifier

A silicon controlled rectifier or semiconductor-controlled rectifier is a four-layer solidstate current-controlling
device. The name “silicon controlled rectifier” is General Electric’s trade name for a type of thyristor.
SCRs are mainly used in electronic devices that require control of high
Voltage and power. This makes them applicable in medium and high AC power operations such as motor control
function.

An SCR conducts when a gate pulse is applied to it, just like a diode. It has four layers of semiconductors that
form two structures namely; NPNP or PNPN. In addition, it has three junctions labeled as J1, J2 and J3 and three
terminals Anode,Cathode, Gate.

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