Single-Phase AC Motor Starting Circuit with Zero-Cross Control
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Solution Overview
Problem
Conventional starting circuits for single-phase AC motors face difficulties in control complexity, high production costs, and intricate circuit structures.
Innovation Solution
A starting circuit comprising a rectifying and voltage-stabilizing circuit, a control circuit with a zero-cross detecting circuit and counter, and a bidirectional thyristor, where the bidirectional thyristor is connected to a starting winding and capacitor, with a photoelectric-isolating and driving circuit for safe operation, and an adjustable counter for controllable switching.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional starting circuit with current-measuring circuit, rectifying circuit, comparing circuit, and bidirectional thyristor is used, then the motor starting function is achieved, but the control complexity increases and production cost increases
Solution Approach 1:
The patent merges the rectifying circuit and voltage stabilizing circuit into a single integrated module that processes AC input voltage. The zero-cross detecting circuit and counter are combined to form a unified control mechanism that tracks voltage cycles and triggers the bidirectional thyristor at precise moments. This consolidation reduces the number of separate components and simplifies the overall circuit architecture while maintaining reliable motor starting function.
Solution Approach 2:
The bidirectional thyristor serves multiple functions: it acts as the main switching element for motor starting, is controlled by the counter-based timing mechanism, and its switching state is monitored by the protection circuit. The rectifying and voltage-stabilizing circuit simultaneously performs both rectification and voltage regulation. This multi-functionality reduces the need for additional specialized components.
2Reliability
If a conventional starting circuit with multiple separate circuits is used, then the motor starting function is achieved, but the production cost increases
Solution Approach 1:
By combining the rectifying and voltage-stabilizing functions into a single circuit module, and integrating the zero-cross detection with the counter mechanism, the patent reduces the total component count. Fewer discrete components mean lower material costs, simplified assembly processes, and reduced manufacturing complexity, directly lowering production costs while maintaining motor starting reliability.
3Device complexity
If the bidirectional thyristor is controlled without precise timing, then the circuit is simpler, but the starting winding operation time cannot be controlled
Solution Approach 1:
The counter is pre-configured with a predetermined count value that corresponds to the desired starting winding operation duration. The zero-cross detecting circuit continuously monitors the AC input voltage and counts each zero-crossing event. When the counter reaches the predetermined value, it automatically triggers the bidirectional thyristor to switch off at the appropriate moment. This preliminary setup enables precise timing control without requiring complex real-time calculations or additional sensing mechanisms.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution simplifies the circuit structure, reduces production costs, enables easy control, ensures safety, and allows adjustable turn-on and operation times for the starting winding, making it efficient and reliable.
Implementation Method 1
the zero-cross detecting circuit operates to detect zero crossing points of the utility power AC input
Implementation Method 2
an output end of the rectifying and voltage-stabilizing circuit operates to supply power to the control circuit
Implementation Method 3
a photoelectric-isolating and driving circuit is disposed between the counter and the bidirectional thyristor
Data Source
AI summary
A starting circuit for a single-phase AC motor, consisting at least-of a rectifying and voltage-stabilizing circuit, a control circuit with a zero-cross detecting circuit and a counter, and a bidirectional thyristor. The bidirectional thyristor is serially connected to a starting winding and a starting capacitor, the bidirectional thyristor, the starting winding and the starting capacitor are connected a utility power AC input. The input end of the rectifying and voltage-stabilizing circuit is connected to the utility power AC input. The output end of the rectifying and voltage-stabilizing circuit supplies power to the control circuit. The input end of the zero-cross detecting circuit is connected to the utility power AC input. The output end of the zero-cross detecting circuit is connected to the input end of the counter.