Single-Phase Brushless Motor Drive Circuit Zero-Cross Detection
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Solution Overview
Problem
Single-phase brushless motors face challenges with the 'dead point' issue, where the rotor fails to rotate when a driving current is supplied, and the use of Hall elements for position detection increases costs and reduces miniaturization due to precision errors and the need for magnetic field testing.
Innovation Solution
A driving circuit that generates alternating driving currents with de-energized periods, includes a zero-cross detecting circuit to determine the length of energized periods, and starts detection after a predetermined time, allowing for efficient operation without a Hall element, enabling miniaturization and cost reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Hall elements are used for position detection, then rotor position detection precision is improved, but device complexity and cost increase due to additional components and magnetic field testing requirements
Solution Approach 1:
The invention extracts and eliminates the Hall element from the motor structure, replacing it with a control circuit that detects rotor position through induced voltage measurements during de-energized periods. This removes the need for magnetic field sensors and their associated testing procedures, directly reducing device complexity while maintaining position detection capability
Solution Approach 2:
The invention substitutes the mechanical/magnetic sensing system (Hall element detecting magnetic field changes) with an electrical measurement system (control circuit detecting induced voltage). This replacement eliminates the need for magnetic field testing and additional components, resolving the contradiction between detection precision and device complexity
2Measurement precision
If Hall elements are incorporated into the motor, then position detection capability is improved, but motor size increases due to additional components
Solution Approach 1:
The Hall element is extracted from the motor structure, eliminating the need for additional sensors and their mounting space. The control circuit uses existing motor windings to generate detection signals, thereby reducing motor volume while maintaining position detection capability
Solution Approach 2:
The motor windings serve dual purposes: generating driving current and producing induced voltage for position detection during de-energized periods. This multi-functionality eliminates the need for separate sensing components, reducing motor size while maintaining detection capability
3Measurement precision
If de-energized periods are introduced in driving current, then rotor position detection accuracy is improved, but energy consumption increases due to intermittent current supply
Solution Approach 1:
The invention employs periodic de-energized periods during which induced voltage is measured for position detection. These brief intervals allow accurate rotor position determination without continuous current supply, improving detection accuracy while limiting energy consumption to necessary driving periods only
Solution Approach 2:
The motor winding generates its own induced voltage during de-energized periods, which is directly utilized for position detection. This self-service mechanism eliminates the need for external sensing components and continuous power supply, achieving accurate detection with minimal energy consumption
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 effectively addresses the 'dead point' issue and reduces the size and cost of motor driving ICs, enabling miniaturization and precise rotor position detection without Hall elements, improving motor efficiency and reducing manufacturing complexities.
Implementation Method 1
an induced voltage, generated across the driving coil, during the de-energized period
Data Source
AI summary
A driving circuit for a single-phase brushless motor includes: a driving-signal-generating circuit to generate a driving signal for supplying first and second driving currents to a driving coil of the single-phase brushless motor in an alternate manner with a de-energized period therebetween; an output circuit to supply the first or the second driving current to the driving coil in response to the driving signal; and a zero-cross detecting circuit to detect a zero cross of an induced voltage, generated across the driving coil, during the de-energized period, wherein the driving-signal-generating circuit determines a length of a subsequent energized period, based on a driving cycle from a start of an energized period to a time when the zero-cross detecting circuit detects the zero cross, and the zero-cross-detecting circuit starts detection of the zero-cross after a predetermined time period has elapsed from a start of the de-energized period.