Programmable Power Switch Two-Level Current Sensing
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Solution Overview
Problem
Existing power distribution switches face challenges in high-current applications due to low sensitivity in current sensing, especially when current limits are programmable, leading to potential dangers and increased errors from circuit non-idealities such as transistor mismatches and offsets.
Innovation Solution
A programmable power distribution switch with two-level current sensing, utilizing a reference voltage generator and current limiter to accurately sense and limit currents, maintaining sensitivity across the range of current limits by selectively turning on/off transistors to adjust current paths and minimize errors from circuit offsets.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a small field effect transistor and a sense resistor are placed in parallel with the main power FETs to sense current in high-current applications, then current sensing becomes possible without inserting a resistor in the current path, but the sensitivity of current sensing becomes low
Solution Approach 1:
The patent divides the current sensing function into two distinct circuits: a first current sensing circuit using a sense resistor for high-current range detection, and a second current sensing circuit using transistor gate voltage for low-current range detection. This segmentation allows each circuit to operate optimally in its designated range, resolving the sensitivity limitation of the single parallel FET-resistor approach.
Solution Approach 2:
The patent transitions from sensing current directly through voltage drop across a resistor to sensing current by measuring the gate voltage of the FET, which is another dimension of the same electrical parameter. This dimensional change enables high-precision sensing in the low-current range where direct resistor sensing becomes ineffective.
2Adaptability or versatility
If current limit programmability is added by including an adjustable reference current to control the current limit, then current limits can be programmed, but the sensitivity of current sensing becomes even lower due to reduced voltage drop over the sense resistor
Solution Approach 1:
The patent implements dynamic switching between two current sensing circuits based on the operating current range. The system automatically selects the appropriate sensing circuit (first or second) depending on whether the current is in the high-current or low-current range, maintaining high sensitivity across the entire programmable current limit range while enabling flexible current limit programming.
Solution Approach 2:
The patent changes the sensing parameter from voltage drop across a fixed sense resistor to the gate voltage of the FET, which can be dynamically adjusted. This parameter change allows the system to maintain high sensing sensitivity across different programmable current limits, overcoming the limitation of reduced voltage drop when current limits are lowered programmatically.
3Adaptability or versatility
If the current limit is lowered programmatically while keeping the sense resistor constant, then current limits can be adjusted, but the voltage drop over the resistor is reduced resulting in increasing current sensing error due to circuit non-idealities
Solution Approach 1:
The patent segments the current sensing function into two specialized circuits: one optimized for high-current measurement using a sense resistor, and another optimized for low-current measurement using FET gate voltage sensing. This segmentation allows the system to maintain high accuracy across the entire programmable current limit range, eliminating the accuracy degradation that occurs when using a single sense resistor approach.
Solution Approach 2:
The patent introduces the FET gate voltage as an intermediary measurement parameter that indirectly reflects the current flowing through the FET. This intermediary measurement approach provides high-precision current sensing in the low-current range without requiring a large voltage drop across a sense resistor, thereby maintaining accuracy across programmable current limits.
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 solution allows for setting current limits closer to the maximum rated current, reducing the risk of damage from overcurrent conditions while maintaining accurate current sensing, even at lower programmability levels, thus enhancing safety and reliability.
Implementation Method 1
a programmable output device having a resistance based on a programmed maximum output current and generates an output voltage based on the resistance and a load current
Implementation Method 2
a reference voltage generator that is configured to generate a reference voltage corresponding to the output voltage when the load current is substantially equal to the programmed maximum output current
Implementation Method 3
A current limiter is also included to reduce the load current in response to a comparison of the output voltage and the reference voltage, when the comparison is indicative of the load current exceeding the programmed maximum output current
Data Source
AI summary
Programmable power distribution switches with two-level current sensing are disclosed. In a particular example, a power distribution switch includes a programmable output device having a resistance based on a programmed maximum output current and generates an output voltage based on the resistance and a load current. The example power distribution switch also includes a reference voltage generator that is configured to generate a reference voltage corresponding to the output voltage when the load current is substantially equal to the programmed maximum output current. A current limiter is also included to reduce the load current in response to a comparison of the output voltage and the reference voltage, when the comparison is indicative of the load current exceeding the programmed maximum output current.