Motor Control Circuit Current Limiting for Electronic Timepiece
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Solution Overview
Problem
Existing motor control circuits for electronic timepieces often result in high current consumption due to frequent switching of the motor drive unit between ON and OFF states, especially when the current waveform rapidly rises or falls, leading to increased through-current and charge/discharge currents.
Innovation Solution
A motor control circuit that includes a drive unit with ON and OFF states, lower and upper limit detection units, and a drive control unit that secures a minimum elapsed time for each state, reducing the switching frequency by delaying the transition from ON to OFF based on detected current thresholds and elapsed times, thereby simplifying the control circuit configuration and reducing current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the drive unit is controlled to be brought into the ON state and the OFF state through mere comparison between the current, and the upper limit current value and the lower limit current value, then the control circuit configuration is simplified, but the switching frequency increases and current consumption increases
Solution Approach 1:
The control circuit performs preliminary actions by setting predetermined time periods before the drive unit switches states. When the current exceeds the upper limit, the control circuit waits for a predetermined time period before turning off the drive unit. Similarly, when the current falls below the lower limit, the control circuit waits for a predetermined time period before turning on the drive unit. This preliminary timing action prevents frequent switching and reduces current consumption while maintaining a relatively simple control circuit configuration.
2Use of energy by moving object
If the drive unit is brought into the OFF state immediately when the current exceeds the upper limit current value, then the current consumption is reduced, but the drive unit switches frequently and current consumption increases due to through-current and charge/discharge current
Solution Approach 1:
The control circuit implements a predetermined time period delay before switching the drive unit state. When the current exceeds the upper limit, the control circuit does not immediately turn off the drive unit but waits for a predetermined time period. This preliminary timing action reduces the switching frequency and prevents frequent on-off cycling that causes through-current and charge/discharge current, thereby reducing overall current consumption.
3Measurement precision
If the polarity switching is determined on the basis of both ON period and OFF period, then the motor rotation is precisely controlled, but the control circuit configuration becomes complex
Solution Approach 1:
The control circuit extracts and utilizes only the OFF period (or only the ON period) for determining polarity switching timing, rather than requiring both ON and OFF periods. By taking out just the necessary timing parameter, the control circuit achieves sufficient motor rotation control precision while significantly simplifying the control circuit configuration compared to methods requiring both period measurements.
Data Source
AI summary
A motor control circuit includes a driver having ON and OFF states, and outputs a drive signal to a coil of a motor, a lower limit detector detecting whether current flowing through the coil is less than a lower limit, an upper limit detector detecting whether current flowing through the coil is more than an upper limit, a drive controller placing the driver into the ON state based on a detection result in the lower limit detector after the driver is brought into the OFF state, and placing the driver into the OFF state when the upper limit detector detects that the current is more than the upper limit after a predetermined time elapses from the driver being placed in the ON state, and a polarity switcher switching a polarity of the drive signal when an OFF time of the driver satisfies a polarity switching condition.