Analog Current Control Loop with Digital Feedback for Inductive Loads
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Solution Overview
Problem
Closed loop control systems using analog circuits face challenges with Hall effect current sensors, which have response time limitations, leading to overshoot errors when controlling current flow to inductive loads due to their slower bandwidth and response time.
Innovation Solution
A digital feedback mechanism is introduced by adding a supplemental signal to the measured current signal from a Hall effect sensor, using the state of the output switch to enhance the control loop's response, allowing for quicker reaction to current changes without requiring additional analog measurements or complex circuits.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a Hall effect current sensor is used in an analog control circuit, then current measurement is achieved, but the response time is too slow (5-10 microseconds) to prevent overshoot in low inductance loads
Solution Approach 1:
The patent applies preliminary action by adding an accelerator signal that anticipates the slow sensor response. The accelerator circuit generates a supplemental signal proportional to the switch drive signal, effectively predicting the current rise before the Hall sensor can detect it. This preliminary action compensates for the inherent 5-10 microsecond delay, allowing the control circuit to respond appropriately without waiting for the slow sensor to catch up.
Solution Approach 2:
The patent introduces an intermediary accelerator circuit between the switch driver and the control input. This intermediary generates a supplemental signal that bridges the gap between the fast switch transitions and the slow Hall sensor response. The accelerator circuit acts as a mediator, translating the fast switch drive signal into a compensating signal that accounts for the sensor's slow response, thereby enabling the slow sensor to effectively control fast-switching circuits.
2Measurement precision
If the control circuit waits for the Hall effect sensor to respond, then accurate current measurement is obtained, but overshoot occurs before the sensor output reaches the proper value
Solution Approach 1:
The patent applies preliminary anti-action by introducing an accelerator signal that counteracts the expected overshoot before it occurs. The accelerator circuit generates a supplemental signal that is added to the Hall sensor output, creating a composite feedback signal that anticipates and compensates for the upcoming overshoot condition. This preliminary counter-action prevents the control circuit from reacting too late, thereby maintaining reliable control even though the Hall sensor itself is slow.
3Speed
If a faster current sensor is used to reduce response time, then overshoot is reduced, but the system complexity and cost increase
Solution Approach 1:
The patent applies copying by creating an accelerated copy of the Hall sensor output through the accelerator circuit. Instead of replacing the slow Hall sensor with a fast sensor, the system creates a supplemental accelerated signal that mirrors and enhances the sensor output. This copied and accelerated signal allows the system to achieve fast response characteristics while retaining the simple, inexpensive Hall sensor, thereby avoiding the complexity and cost of faster sensors.
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 effectively reduces overshoot errors and improves the control circuit's responsiveness, ensuring accurate current regulation by compensating for the slow response time of Hall effect sensors, thereby preventing excessive current flow.
Implementation Method 1
the task of using a single set point analog control circuit to control the load current to an output device using a Hall effect current sensor is difficult
Data Source
AI summary
A circuit for controlling current flow to an associated inductive load is provided. The circuit includes a switching element having an open state and a closed state that intermittently connects an associated power supply to the inductive load when the switching element is in the closed state, a switch driver that generates a switch drive signal provided to a control element of the switch that controls the state of the switch to be the open state or the close state based on a desired load current set point and a feedback signal, a current sensor that measures a current flowing through the switching element and the load and generates a sensed current signal, and a summing circuit that adds a representation of the sensed current signal and a supplemental signal comprising a representation of the switch drive signal to generate the feedback signal.