High Side Voltage Switch with Current Mirror Protection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional transistor-based switch circuits face issues with high output current peaks, voltage drop, and increased complexity due to additional current sensing circuits, which are problematic in low power applications and manufacturing.
Innovation Solution
A high side voltage switch circuit is developed with auto-limited current capabilities by incorporating a cascode transistor into the current mirror circuit, reducing output current peaks and minimizing voltage drop through strategic transistor sizing and shut-off mechanisms.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a simple transistor switch is used, then the voltage drop is minimal, but the output current varies significantly and can become excessively high
Solution Approach 1:
A current mirror circuit is introduced as an intermediary mechanism between the control signal and the transistor switch. The current mirror (comprising transistors Q1-Q4 and resistors R1-R2) senses the output current and generates a control voltage that automatically regulates the transistor gate, thereby limiting peak current while maintaining low voltage drop during normal operation.
Solution Approach 2:
The patent implements negative feedback through the current mirror circuit that continuously monitors the output current and adjusts the transistor gate voltage accordingly. When output current increases, the feedback mechanism reduces the gate drive to limit the current, creating a self-regulating system that maintains reliable current control.
2Reliability
If additional current sensing circuits are added to control output current, then current control improves, but device complexity and manufacturing cost increase
Solution Approach 1:
The current mirror circuit serves multiple functions simultaneously: it limits peak current, provides temperature compensation, and stabilizes the switch operation across varying conditions. By combining these functions into a single integrated circuit block rather than separate components, the patent achieves reliable current control without proportionally increasing complexity.
Solution Approach 2:
The patent merges the current sensing, current limiting, and temperature compensation functions into a unified current mirror circuit architecture. This integration reduces the number of discrete components and interconnections compared to implementing each function separately, thereby controlling overall device complexity while achieving multiple performance goals.
3Reliability
If a current mirror circuit is used to limit output current, then current control improves, but voltage drop increases
Solution Approach 1:
The patent employs dynamic operation where the current mirror circuit actively adjusts its impedance characteristics based on the operating conditions. During transient high-current events, the current mirror presents high impedance to limit current. During steady-state normal operation, the transistor switch operates in a low-impedance state minimizing voltage drop, achieving both current control and energy efficiency at different times.
Solution Approach 2:
The current mirror circuit is designed to exert its current-limiting action only when necessary (during startup, transients, or fault conditions) rather than continuously. The activation transistor Q5 and associated circuitry ensure the current mirror engages only when peak current protection is needed, allowing the main transistor switch to operate with minimal voltage drop during normal conditions.
4Loss of energy
If transistor sizing is optimized for low voltage drop, then energy loss decreases, but peak current increases
Solution Approach 1:
The patent utilizes parameter changes in the transistor operating conditions to resolve the contradiction. The transistor switch is sized for low on-resistance to minimize voltage drop, while the current mirror circuit dynamically adjusts the effective operating parameters (gate voltage, drain current) to limit peak current. This allows the transistor to operate in different regions of its characteristic curves depending on the situation.
Data Source
AI summary
A method and apparatus are described for providing a current mirror type high voltage switching circuit (60) having a reference branch (M2, M3, R1) and a tracking branch (M1, M5), where the output peak current is limited by adding an additional branch (M4, M6) to the current mirror circuit which includes an additional mirror transistor (M4) and cascode transistor (M6), and where over voltage protection is provided by including a shut-off circuit (Q1, Q2) which turns “OFF” the cascode transistors (M5-M8) whenever the output voltage (Vout) exceeds the first reference voltage (Vbat) by a predetermined amount.