PWM Inductive Load Current Control Using MOSFET Current Estimation
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Solution Overview
Problem
Current solutions for controlling current in inductive loads, such as electro-mechanical valves, face challenges in achieving accurate and linear current control due to high costs and limited accuracy, particularly in automotive applications where precise control is required, often necessitating multiple power stages and current-sensing circuitry, which can be costly and pin-count intensive.
Innovation Solution
A circuit and method utilizing a PWM current controller with a negative feedback loop incorporating proportional, integral, and derivative control actions, coupled with a median current estimation based on low and high current values during ON and OFF periods, allows for real-time current regulation using a single low-side switch and an external recirculation diode, enabling accurate current control without the need for extensive microprocessor workload or additional power stages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If multiple power stages and current-sensing circuitry are used to achieve accurate current control, then current control accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent extracts the current-sensing function from the main power stage by using the inherent voltage drop across the low-side switch during its ON state. This allows current measurement without requiring separate sensing circuitry for both ON and OFF states, reducing overall device complexity while maintaining measurement precision.
Solution Approach 2:
The low-side switch serves dual functions: it acts as a power switching element for current control and simultaneously functions as a current sensing element through its on-state voltage drop. This multi-functionality reduces the need for separate dedicated sensing components, addressing both accuracy and complexity requirements.
2Measurement precision
If multiple power stages and current-sensing circuitry are used to achieve accurate current control, then current control accuracy is improved, but cost increases
Solution Approach 1:
The patent extracts the current-sensing function from the main power stage by using the inherent voltage drop across the low-side switch during its ON state. This allows current measurement without requiring separate sensing circuitry for both ON and OFF states, reducing overall device complexity while maintaining measurement precision.
Solution Approach 2:
The patent utilizes the naturally occurring voltage drop across the low-side switch, which is already present during normal operation, as the sensing mechanism. This approach avoids the need for expensive dedicated sensing components, achieving accurate current measurement at lower cost by leveraging an existing system element.
3Measurement precision
If extensive microprocessor workload is used for current control, then control accuracy is improved, but processing time and system complexity increase
Solution Approach 1:
The patent replaces complex microprocessor-based current control algorithms with an analog proportional-integral controller that directly processes the voltage drop signal. This substitution of mechanical/electronic control for computational control reduces processing time and eliminates the need for extensive microprocessor workload while maintaining control accuracy.
Solution Approach 2:
The patent implements a proportional-integral feedback controller that continuously monitors the voltage drop across the low-side switch and adjusts the PWM duty cycle accordingly. This closed-loop feedback mechanism provides accurate current control through simple analog computation rather than complex digital processing, reducing both processing time and system complexity.
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
This approach provides real-time current control with high accuracy, reducing costs and pin count requirements while maintaining precise control across a wide range of current values, even in non-linear valve behaviors, and is suitable for applications requiring tight current regulation.
Implementation Method 1
a controllable switch, in particular a MOSFET, which is switched on to increase a load current flowing in the inductive load
Implementation Method 2
a recirculation diode arranged to re-circulate the load current when the controllable switch is switched off
Implementation Method 3
When a current is flowing through such coil, the magnetic field generated is producing a force on the core, winning the opposition of a spring and causing the core movement
Data Source
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AI summary
Circuit for controlling the current in inductive loads, in particular electro-mechanical valves comprising a coil, comprising a driver circuit (20; 30) to drive a load current (Iload) in said inductive load (50), said driver circuit (20; 30) including a pair of low side and a high side driving switches (11, 22) obtained by a controllable switch (11), in particular a MOSFET, which is switched on to increase a load current flowing in the inductive load (50), and by a recirculation diode (22) arranged to re-circulate the load current (Iload) when the controllable switch is switched off, said controlling circuit including a control module (25; 35) generating a control signal (CMD) to switch on and off the controllable switch (11). In the solution described, said control module (35) includes a PWM (Pulse Width Modulation) current controller module (35), comprising a negative feedback closed loop comprising a module implementing at least a proportional control action and a integral control action feeding a PWM modulator module, said PWM current controller module (35) receiving as feedback loop setpoint a target current value (Itarget) and as feedback measured value of the loop an estimated value (Imid) of the current flowing in the load (ILS) during a measurement PWM cycle (i+1), said PWM current controller module (35) being configured to generate said control signal (CMD) for a control input of the controllable switch (11) on the basis of an error (Ierror) between said target current (Itarget) and said estimate (Imid) of the current (ILS) flowing in the load (50).