Detection circuit and method for zero crossing point of alternating current power supply

Abstract

The invention discloses a detection circuit and method for a zero crossing point of an alternating current power supply. A half-wave shaping circuit is formed by a current limiting resistor and a light-emitting diode, a cathode of a protective diode is connected with the current limiting resistor, and the other end of the current limiting resistor is connected with an input end of the alternating current power supply; and a photistor collector is connected with a singlechip and a direct current power supply through another light-emitting diode. The singlechip firstly detects twice level trip interruption time t1 and t3 of a previous alternating current power supply positive half-wave, calculates a previous wave crest moment t2, then detects the twice level trip interruption time t4 and t6 of a next alternating current power supply positive half-wave and a wave crest time t5 at the time to obtain an alternating current power supply period, and outputs a control signal to control a thyristor to be accurately triggered with a next zero crossing point moment as a benchmark. The detection circuit and method for the zero crossing point of the alternating current power supply enhance the driving capacity of a voltage without other gate circuits, has no requirements on amplitude and frequency of the alternating current power supply and no limits on a working voltage of the light-emitting diode and can allow a voltage value of the alternating current power supply to fluctuate in a large range.

Description

technical field The invention relates to a detection circuit and a detection method for a zero-crossing point of an AC power supply, which are applied in a phase-shifting control circuit of a thyristor and belong to the field of electrical engineering. Background technique Zero-crossing detection means that the zero-crossing point of the AC voltage is automatically detected, and then the zero-crossing point is used as the reference point to control the conduction of the electronic switch according to the phase shift angle. It is often used in power control devices where the thyristor is used as a switching device. Since the thyristor can only be turned on when the anode is positively biased to the cathode and the control electrode is also positively biased to the cathode, the accurate detection of the zero-crossing point of the AC power supply becomes extremely critical, because the determination of its value directly determines Reference point for sync signal. At the same ...

AI Technical Summary

Problems solved by technology

In order to overcome the above-mentioned deficiencies in the prior art that the accuracy of the synchronous trigger signal of the thyristor zero-crossing point is affected by the level of the input voltage, and that the trigger signal is likely to cause misoperation and cannot be accurately triggered, it provides a zero-crossing detection circuit of an AC power supply. The detection circuit has nothing to do with the level of the input voltage, protecting the thyristor and its load from the impact of surge

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