High-Side Switch Feedback Circuit for Accurate Sensor Current Limiting
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Solution Overview
Problem
High-side switches used in power supplies for sensors, such as ultrasonic sensors, face issues with current limitation and voltage feedback errors due to resistors in the current path, leading to unwanted current flow and voltage changes, which are significant at higher currents and not negligible, necessitating multiple switches or large tolerance in current limitation.
Innovation Solution
A high-side switch design with a measuring transistor, power transistor, and a comparator that applies a compensation current to the control input of the measuring transistor to counteract voltage errors and adjust current flow, allowing precise power supply and diagnostics without additional switches or increased current errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If resistors are added to the current path for current limiting, then current control capability is improved, but voltage feedback errors increase causing current flow errors
Solution Approach 1:
The patent implements a feedback mechanism where the voltage at the control input of the power transistor is sensed and fed back to adjust the gate voltage dynamically. This compensates for the voltage feedback errors introduced by the resistors, maintaining accurate current control despite the presence of current-limiting resistors in the current path.
Solution Approach 2:
The patent changes the electrical parameters (voltage and current) at the control input of the power transistor dynamically based on the load conditions. By adjusting the gate voltage according to the actual current flow and voltage drops, the system maintains precise control across varying operating conditions, offsetting the errors introduced by fixed resistors.
2Power
If multiple high-side switches are used to handle higher currents, then current handling capability is improved, but device complexity increases
Solution Approach 1:
The patent designs a single high-side switch that can handle a wide range of current levels by dynamically adjusting its operating parameters through feedback control. This multi-functional approach allows one switch to replace multiple switches, as it can adapt its current handling capability based on the connected sensor's requirements without requiring parallel switch configurations.
Solution Approach 2:
The patent introduces dynamic control of the power transistor's gate voltage to enable a single switch to handle varying current levels. Instead of using multiple fixed-capacity switches, the system dynamically adjusts the single switch's operating point to match the required current, simplifying the overall device architecture while maintaining high current handling capability when needed.
3Measurement precision
If resistor values are reduced to minimize voltage drop, then voltage feedback errors are reduced, but current limiting capability deteriorates
Solution Approach 1:
The patent uses feedback control to compensate for the effects of low-value resistors. By sensing the actual voltage at the control input and adjusting the gate voltage accordingly, the system maintains accurate current limiting even with minimal voltage drops across the resistors, resolving the trade-off between feedback accuracy and current control capability.
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 effectively reduces current errors and allows precise, stepwise adjustable power supply to sensors, enabling operation with higher currents without significant voltage drops or increased power transistor current errors, while also enabling simple diagnostics and cost-effective implementation.
Implementation Method 1
the (measuring) resistance in the current or reference path causes undesirable (source) negative feedback, which alters the voltage at the control input of the power transistor
Implementation Method 2
A first calibratable current source is electrically connected to the control input of the measuring transistor
Data Source
Figure 1
Figure 2
AI summary
The invention relates to a high-side switch (100) for supplying power to at least one sensor, comprising two connections (1, 2) and a current path (10) via which the connections (1, 2) are connected together and within which a measurement transistor (4) and at least two resistors (5) are connected in series. The high-side switch (100) further comprises a power transistor (6) which is connected in parallel to the current path (10) and has a comparator (30) that has two inputs (31, 32), one of which is connected to the current path (10) in a fixed manner and can be variably connected to the current path (10) such that the number of resistors (5) lying between the connection points of the inputs (31, 32) to the current path (10) can be changed. The comparator (30) also comprises an output (33) which is connected to the control input of the measurement transistor (4) and the power transistor (6). A first current source (40) which can be calibrated is connected to the control input of the measurement transistor (4).