Constant-Current Controller for Inductive Loads Using PWM Switching
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Solution Overview
Problem
Existing systems for powering inductive loads in electromechanical devices, such as solenoids and DC motors, face inefficiencies due to varying current requirements for locking and unlocking states, leading to high standby current consumption and energy wastage.
Innovation Solution
A constant-current controller using a switching circuit with pulse-width modulation (PWM) to maintain a consistent current in inductive loads, employing a primary and secondary switch configuration that adjusts voltage and current flow based on switching frequency, allowing for efficient power management in devices like solenoids and DC motors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If solenoid is used to drive electromechanical door latch, then locking function is achieved, but standby current consumption is high (0.5 A)
Solution Approach 1:
The patent replaces the solenoid (electromagnetic system) with a DC motor (electromechanical system) to drive the door latch. The DC motor uses a gear train and spring mechanism to achieve locking, eliminating the need for continuous high current to maintain the locked state. The motor only consumes high current during the actuation phase, while standby current is reduced to approximately 15 mA through the mechanical holding mechanism.
2Loss of energy
If constant current is provided to inductive load, then energy efficiency is improved, but requires complex control circuitry
Solution Approach 1:
The patent employs pulse-width modulation (PWM) to provide periodic current pulses to the DC motor instead of continuous constant current. The controller switches the power supply on and off at high frequency, adjusting the duty cycle to control average current. This periodic action achieves efficient energy delivery during motor actuation while minimizing standby power consumption, and the PWM technique is well-established in motor control applications.
3Reliability
If pick current is much greater than hold current, then solenoid can achieve locking, but current variation leads to energy inefficiency
Solution Approach 1:
The patent uses a DC motor with a gear train and spring mechanism that dynamically transitions from high-torque mode during actuation to low-power mechanical holding mode. The motor delivers high current during the brief actuation phase to overcome spring force and engage the latch, then the mechanical gear-spring system maintains the locked position with minimal electrical power, eliminating the continuous high current requirement of solenoids.
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 achieves significant reduction in standby current consumption by maintaining a constant current, optimizing energy use and extending battery life in devices like door latches and strikes by ensuring power is only used when necessary.
Implementation Method 1
the voltage across the inductive load is equal to the source voltage (Vs). At time to, until the end of a time period (T), with the primary switch open and the secondary switch closed, zero volts appears across the inductive load. During this interval, load current continues to flow due to the stored energy in the inductance.
Data Source
AI summary
A constant-current controller that supplies a constant current to an inductive load. This controller comprises an electric control circuit module. The electric control circuit module comprises a primary switch and a secondary switch. During a time interval in which the primary switch is closed (ton), the secondary switch is open and the voltage across the inductive load is equal to the source voltage (Vs). At time ton until the end of a time interval (T), zero volts appears across the inductive load. During this interval, current continues to flow as supplied by the energy stored in the inductance. The periodic current in the inductive load becomes constant with a sufficiently large PWM switching frequency and is dependent upon the parameters of the control circuit and the duration of ton.