Coil PWM Driving Circuit for Stable Inrush and Latching Current
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Solution Overview
Problem
Existing coil driving devices face challenges in consistently supplying predetermined inrush and latching currents across a wide voltage range, leading to inefficiencies, increased power consumption, and heat generation, particularly at low or high voltages, without the need for current sensors or feedback circuits.
Innovation Solution
A coil driving device with an input voltage sensing unit, a PWM circuit unit, an impedance adjustment unit, and a control unit that adjusts the impedance and PWM signal duty ratio and frequency based on the input voltage to manage inrush and latching currents, eliminating the need for current sensors and feedback circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If PWM control is used to maintain constant coil current, then magnetic force is maintained constantly, but device complexity increases due to requiring current sensors, feedback circuits, and photo couplers
Solution Approach 1:
The patent extracts and eliminates the complex feedback control components (current sensors, feedback circuits, photo couplers) from the system. Instead of using PWM control with full feedback, the invention uses a simplified approach with a switching element and timing control to achieve constant coil current without requiring these extracted components, thereby reducing device complexity while maintaining current stability.
2Reliability
If high inrush current is supplied to drive the coil initially, then the moving core is drawn in successfully, but power consumption and heat generation increase
Solution Approach 1:
The patent applies preliminary action by pre-charging a capacitor before the switching element turns on. This stored energy in the capacitor provides the necessary inrush current to reliably draw in the moving core during initial operation. After the core is drawn in, the capacitor is recharged during the off-period, allowing the system to maintain reliable operation while controlling overall power consumption through the timing and duration of the high-current phase.
3Power
If PWM duty ratio is increased to supply sufficient current at low voltage, then coil driving capability is improved, but power consumption and heat generation increase
Solution Approach 1:
The patent uses periodic action through oscillating the switching element between on and off states. During the on-period, the capacitor discharges to provide high current to the coil. During the off-period, the capacitor is recharged through the diode from the power source. This periodic charging and discharging allows the system to deliver high power when needed while controlling average power consumption and heat generation through the duty cycle and timing control, avoiding continuous high power dissipation.
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 device stabilizes inrush and latching current supply across a wide voltage range, reducing power consumption and heat generation, while simplifying the design by eliminating the need for current sensors and feedback circuits, thus enhancing reliability and reducing product size and cost.
Implementation Method 1
an input voltage sensing unit for detecting an input voltage
Implementation Method 2
a pulse width modulation (PWM) circuit unit for outputting a PWM signal for the switching operation of the switch unit
Implementation Method 3
an impedance adjustment unit for changing an impedance value such that the PWM signal is adjusted, thereby limiting the driving current
Implementation Method 4
a switch unit configured to make a switching operation to supply a driving current to a coil
Implementation Method 5
an internal coil acts as an actuator, and when a current flows at the coil, a switch operates to conduct electricity
Implementation Method 6
When power is on, a magnetic force is generated by the fixed core. The moving core is then brought into contact with the fixed core by the magnetic force
Data Source
AI summary
The present disclosure provides a coil driving device comprising: an input voltage sensing unit for sensing an input voltage; a switch unit configured to make a switching operation to supply a driving current to a coil; a PWM circuit unit for outputting a pulse width modulation (PWM) signal for the switching operation of the switch unit; an impedance adjustment unit for varying an impedance value such that the PWM signal is adjusted, thereby limiting the driving current; and a control unit for causing the impedance adjustment unit to vary the impedance value on the basis of the input voltage, thereby adjusting at least one of the duty ratio of the PWM signal and the frequency thereof.