Switch Control Device Zero Cross-Point Detection Noise Immunity
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Solution Overview
Problem
Existing power supply devices using buck converters face challenges in accurately detecting the zero cross-point of input voltage due to noise interference, leading to malfunction of the power switch.
Innovation Solution
A switch control device comprising a self-power voltage biasing circuit, a reference signal generator, and a PWM controller that estimates the zero cross-point of the input voltage and generates a synchronized reference signal to control the switching operation of the power switch, using a high voltage device, comparator, and resistors to divide the power voltage and detect the zero cross period.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage sensing is performed at the input terminal of the power switch, then input voltage information can be obtained, but noise interference occurs when input voltage is close to zero causing zero cross-point detection failure
Solution Approach 1:
The patent introduces an intermediary voltage division circuit that senses voltage at a point other than the noisy input terminal of the power switch. By using resistors R1 and R2 to divide the voltage at a cleaner sensing point and transmit this intermediate signal to the zero cross detection circuit, the system avoids direct exposure to noise at the power switch terminal while still obtaining accurate voltage information for zero cross-point detection.
2Reliability
If direct voltage sensing at power switch terminal is used, then circuit complexity is reduced, but reliable zero cross-point detection cannot be achieved in noisy conditions
Solution Approach 1:
The voltage sensing function is segmented into multiple components: voltage division circuit (R1, R2), zero cross detection circuit, and power voltage generation circuit. This segmentation allows each component to perform its specific function in a optimized manner, with the voltage division circuit providing clean signal, the zero cross detection circuit identifying the precise zero cross-point, and the power voltage generation circuit supplying necessary operating voltage, thereby improving reliability without excessive complexity.
Solution Approach 2:
The voltage division circuit serves multiple functions: it provides voltage scaling for the zero cross detection circuit, generates power voltage for operating the detection circuitry, and creates a buffered signal that isolates the noisy power switch terminal from the sensitive detection circuit. This multi-functionality achieves reliable detection without adding excessive circuit complexity.
Data Source
AI summary
A power voltage required to operate the switch control device is generated by using full-wave current rectification voltage generated by rectifying an AC input. A zero cross-point is detected when a full-wave rectification voltage is zero voltage by using the power voltage. A reference signal synchronized to the full-wave rectification voltage is generated by using the detected zero cross-point. A switching operation of a power switch is controlled by comparing a reference signal with current that flows on the power switch.