This document introduces how to use AC switches to control inductive loads, including control methods, control characteristics and precautions.
The document describes the specific considerations required when controlling inductive loads such as magnetrons, valves, induction motors, and universal motors with AC switches like Triacs. It details the causes of high inrush currents at turn-on, including inductive load behavior and magnetic core saturation due to remanent induction.
Key technical points covered include the impact of trigger timing relative to mains voltage zero crossings, the necessity of managing gate pulse width to ensure device latching, and strategies for synchronizing gate control with lagging current waveforms. The note also provides typical examples, such as controlling a magnetron in a microwave oven, illustrating how improper triggering can lead to component damage or non-compliance with electromagnetic compatibility standards.
High inrush current is caused by the turn-on delay relative to the mains voltage zero point and magnetic core saturation due to remanent induction.
If the first half-cycle conduction is in the same polarity as the previous one, the transformer reaches saturation very rapidly and behaves like a short circuit.
It is better to ensure that the device is switched-on at a different polarity compared to the last half-cycle conduction.