Single Phase Half Wave Controlled Rectifier with R Load | New Topic 2025

In this note, we will discuss the Single Phase Half Wave Controlled Rectifier with R Load. Welcome to Poly Notes Hub, a leading destination for Engineering Notes for Diploma and Degree engineering students.

Author Name: Arun Paul.

What is Single Phase Half Wave Controlled Rectifier with R Load?

The single phase half wave rectifier with R Load is a fundamental power electronics circuit that converts alternating current (AC) to direct current (DC). It uses a single thyristor to control the output voltage and is ideal for resistive loads. This type of rectifier is an important building block for understanding controlled rectification and is commonly used in low-power DC drives, heating applications, and battery chargers.

A single-phase half-wave Controlled rectifier operates by controlling the conduction of a single thyristor (SCR) or diode. It lets current to flow only during the positive half-cycle of the AC input while blocking the negative half-cycle, resulting in a pulsing DC output.

Circuit Diagram of Single Phase Half Wave Controlled Rectifier with R Load

The primary components of a single phase half wave Controlled rectifier with R load are –

• AC Supply: The sinusoidal input voltage comes from a single-phase alternating current voltage source.
• Thyristor or SCR: A silicon-controlled rectifier (SCR) serves as the controlled rectifying element. It only allows conduction when a gate pulse is applied and prevents current flow during the negative half-cycle of the AC input.
• Resistive Load: A totally resistive load guarantees that the current through it is proportional to the voltage across it.
• Gate Trigger Circuit: A gate pulse is given to the thyristor to start conduction at a predetermined firing angle.

Working Principle of Single Phase Half Wave Controlled Rectifier with R Load

The single phase half wave Controlled rectifier with R Load operates in two phases: positive and negative half-cycles of the alternating current source.

• During the positive half-cycle, the anode of the thyristor is positive in comparison to its cathode. However, the thyristor does not conduct right away since it requires a gate trigger to activate. At the firing angle, a gate pulse is sent to the thyristor, forcing it to turn on. When activated, the thyristor conducts, and the output voltage across the resistive load follows the input voltage from to.
• During the negative half-cycle, the anode of the thyristor turns negative in relation to the cathode. As a result, the thyristor switches off and no current passes through the load.
• The output voltage is 0 during this phase. When the current flowing through the thyristor reaches zero at the end of the positive half-cycle, it automatically switches off. This procedure is referred to as natural commutation.

The single-phase half-wave rectifier with a R load is one of the most basic rectifier circuits, and it serves as an important learning tool in power electronics. However, its large ripple factor and low efficiency make it unsuitable for high-power applications. Full-wave or bridge rectifiers are preferred for superior performance. Nonetheless, for fundamental low-power applications, this rectifier remains an affordable and simple choice.

Advantages of Single Phase Half Wave Controlled Rectifier with R Load

Here are some advantages of this circuit –

• Simple circuit design with a single thyristor.
• Controllable DC output voltage by adjusting the firing angle .
• Ideal for low-power applications with resistive loads.

Disadvantages of Single Phase Half Wave Controlled Rectifier with R Load

Here are some disadvantages of this circuit –

• High harmonic distortion in the output voltage and current.
• Not suitable for inductive loads without additional components (e.g., freewheeling diodes).
• Limited efficiency due to discontinuous conduction in the negative half cycle.

Applications of Single Phase Half Wave Controlled Rectifier with R Load

Here are some applications of this circuit –

• Used in low powered motors to controlled them.
• Used in battery charging systems.
• Used in controlling the brightness of resistive incandescent lamps.