AC input voltage interruption detection method and circuit

Abstract

A selector selects either a class upper-limit voltage or class lower-limit voltage as the reference voltage of a comparator. A control logic controls the selector and generates a count-up signal or a count-down signal according to the output of the comparator. An up / down counter counts up in response to the reception of the count-up signal from the control logic and counts down in response to the reception of the count-down signal. A digital-analog converter outputs the class upper-limit voltage and class lower-limit voltage according to the digital value output from the up / down counter. A timer is configured so as to be reset by the count-up signal output from the control logic to the up / down counter.

Description

technical field [0001] The present invention relates to an AC input voltage cutoff detection method and circuit for detecting that the AC input voltage is cut off, and performing stop of a power supply, discharge of a high-voltage capacitor, and the like. Background technique [0002] The AC input voltage interruption detection circuit is used to detect the interruption of the AC input voltage, stop the power supply connected to the AC input voltage, discharge the high-voltage capacitor, etc., and is necessary for safe operation of the AC-DC rectifier, etc. circuit. [0003] figure 1 and figure 2 It is a figure for explaining the conventional 1st AC input voltage interruption detection circuit shown in the following patent document 1, and its operation|movement. figure 1 In , when an AC input voltage is connected via a plug connected to an AC power source, the voltage of the smoothing capacitor C0 varies with the change of the AC voltage. However, if the AC input voltag...

AI Technical Summary

Problems solved by technology

[0012] The above-mentioned conventional first AC input voltage cutoff detection circuit has a problem that even when the AC input voltage is connected, if the capacitance component (other than the parasitic capacitance) existing on the detection circuit side due to the diodes D1, D2 A capacitor may be added intentionally for surge countermeasures) and the time constant of the resistors (R1, R2) that discharge the capacitance component becomes large, and the input voltage Vin may not drop to the reference voltage Vref1. In this case, the Misjudged that the AC input voltage has been cut off

At this time, if a fixed AC voltage is used, this problem can be avoided by selecting a reference voltage Vref1 corresponding to a voltage slightly lower than the peak value of the AC input voltage. There is a problem that if the AC input voltage range becomes wider, it becomes difficult to select the reference voltage Vref1

[0013] In addition, although the above-mentioned existing second AC input voltage cut-off detection circuit does not have the problem of misjudgment like the existing first AC input voltage cut-off detection circuit, it needs Larger resistance and / or capacitance, so there is a problem that it is not suitable to form an AC input voltage cut-off detection circuit with an integrated circuit

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