Adaptive Current Limit Circuit for Short-Circuit Power Dissipation
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Solution Overview
Problem
DC-to-DC voltage regulators with source follower power supply configurations face issues such as high power dissipation during short-circuit conditions, which can damage components, and existing constant current sources limit both transient response and power dissipation, making them inadequate for protecting against short-circuits.
Innovation Solution
The implementation of an adaptive current limit circuit that dynamically adjusts current flow through a source follower power supply, providing high current during normal operation and low current during short-circuit conditions, using transistors with varying threshold voltages and resistors to form an adaptive voltage divider.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a constant current source is used to limit current during short-circuit conditions, then power dissipation is reduced and component damage is prevented, but transient response is also limited and the circuit becomes inadequate for protecting against short-circuits
Solution Approach 1:
The patent implements an adaptive current limit circuit that dynamically adjusts the current limit based on operating conditions. The circuit uses multiple transistors with different threshold voltages and resistors to form voltage dividers that sense the output voltage and adjust the current limit accordingly. During normal operation, the current limit is set to allow adequate transient response, while during short-circuit conditions (when output voltage drops below a threshold), the current limit is reduced to prevent excessive power dissipation and component damage.
2Loss of energy
If current is limited to low levels during short-circuit conditions, then power dissipation is reduced, but current is also limited during normal operation reducing the ability to respond to transient conditions
Solution Approach 1:
The patent changes the current limit parameter dynamically based on the output voltage condition. The adaptive current limit circuit monitors the output voltage and adjusts the current limit parameter: when the output voltage is above a threshold (normal operation), the current limit is set to a higher value to allow adequate transient response; when the output voltage drops below the threshold (short-circuit condition), the current limit is reduced to a lower value to minimize power dissipation and prevent component damage.
3Productivity
If high current is provided during normal operation to ensure adequate transient response, then transient response is maintained, but power dissipation increases during short-circuit conditions causing component damage
Solution Approach 1:
The patent implements a feedback mechanism where the adaptive current limit circuit continuously monitors the output voltage and adjusts the current limit accordingly. The circuit uses resistors to form voltage dividers that sense the output voltage level and feed this information back to the current limit control logic. This feedback allows the circuit to distinguish between normal operation (where high current is needed for transient response) and short-circuit conditions (where current must be limited to prevent excessive power dissipation and component damage).
Data Source
AI summary
A power supply circuit includes an amplifier and first and second transistors. The amplifier is configured to provide a drive potential at its output. The first transistor is coupled between a voltage supply terminal and an output terminal, and has a first control terminal coupled to the amplifier output, and is configured to receive at least a portion of the drive potential at the first control terminal. The second transistor is coupled between the first control terminal and the output terminal, and has a second control terminal coupled to the amplifier output. A threshold voltage of the first transistor is lower than a threshold voltage of the second transistor. The second transistor can operate to adaptively reduce the portion of the drive potential at the first control terminal, for example, by the second transistor turning on responsive to a voltage at the output terminal being lower than a voltage level.