Parallel Transistor Hot Swap Protection Circuit
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Solution Overview
Problem
Existing hot swap systems require significant die area and external components for effective short circuit and in-rush current protection, which is inefficient and can cause harm during power-on and power-off sequences.
Innovation Solution
A circuit design using a pass transistor and a small transistor in parallel, with a comparator to manage the connection between input and output voltages, allowing for programmable current limiting and short circuit protection by switching between the transistors based on voltage levels, efficiently utilizing die area and preventing damage from short circuits and high in-rush currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If traditional hot swap protection circuits are used, then short circuit and in-rush current protection is provided, but die area is significantly increased and external components are required
Solution Approach 1:
The patent combines short circuit protection and in-rush current protection functions into a single integrated circuit structure. The pass transistor and small transistor are merged into one parallel configuration, sharing common drain and source connections, with a single comparator controlling both protection functions. This eliminates the need for separate protection circuits and external components, thereby reducing die area while maintaining comprehensive protection.
Solution Approach 2:
The small transistor is designed to serve multiple protection functions simultaneously. It provides both short circuit protection by limiting current during output shorts and in-rush current protection during power-on sequences. The single comparator circuit also serves dual purposes by detecting both short circuit conditions and in-rush current conditions, making the protection system universal and multi-functional.
2Reliability
If separate protection circuits are used for short circuit and in-rush current, then comprehensive protection is achieved, but device complexity and component count increase
Solution Approach 1:
The patent merges separate protection circuits into a unified structure where the pass transistor and small transistor operate in parallel under the control of a single comparator. This consolidated approach provides comprehensive protection against both short circuits and in-rush currents while simplifying the overall circuit architecture and reducing the number of discrete components required.
Solution Approach 2:
The protection circuit is designed with universal functionality where the same hardware components (transistors and comparator) handle multiple protection scenarios. The comparator universally detects both short circuit conditions and in-rush current conditions, and the small transistor universally limits current in both failure modes, eliminating the need for separate dedicated circuits for each protection function.
3Reliability
If power is disconnected during hot swapping, then circuit safety is improved, but system downtime and operational efficiency decrease
Solution Approach 1:
The protection circuits are designed to activate automatically and immediately upon detection of short circuit or in-rush current conditions, without requiring power disconnection. The comparator continuously monitors output conditions and preemptively triggers the small transistor to limit current or the pass transistor to turn off, preventing damage before it occurs and allowing the system to remain powered and operational throughout the hot swap process.
Solution Approach 2:
The protection system provides self-service by automatically detecting and responding to fault conditions without external intervention or power cycling. The integrated circuit monitors its own output conditions and autonomously activates protection mechanisms when needed, enabling safe hot swapping operations while maintaining continuous system operation and eliminating downtime associated with power disconnection and reconnection sequences.
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 protects circuits from short circuits and in-rush currents with minimal components, ensuring the system's safety during hot swapping operations while optimizing die area usage, allowing for efficient and reliable power management without the need for external components.
Implementation Method 1
a comparator is used with one input connected to Vout and the other input to a reference voltage that may be set by a controller
Implementation Method 2
The pass FET is designed with a low RDSon ('on' resistance) while the small FET is designed with an RDSon that will sustain a short circuit
Data Source
AI summary
A circuit that protects from high power-on in-rush currents and short circuits. The circuit has a pass transistor and a parallel smaller transistor. A comparator senses when an output voltage crosses a reference and turns off the pass transistor and turns on the parallel smaller transistor. The parallel smaller transistor has a higher “on” resistance so that the short circuit or the in-rush current does not harm the electronics. When the short circuit or in-rush current condition is removed, the comparator senses this condition and returns to the normal operation where the pass transistor is on and the parallel small transistor is off.