Nonlinear Current Mirror in LDO Regulators for Light-Load Stability
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Solution Overview
Problem
Low-dropout (LDO) regulators face challenges in achieving both low power operation and fast transient response simultaneously, often experiencing stability issues at light load conditions, which can lead to increased power consumption and poor transient performance.
Innovation Solution
The implementation of a nonlinear current mirror in the LDO power field-effect transistor, which adjusts the current mirror ratio to maintain stability and bandwidth during light load conditions while providing constant current during heavy load conditions, thereby enhancing power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a conventional LDO regulator uses a fixed current mirror ratio, then the circuit structure is simple, but the regulator experiences stability issues at light load conditions and cannot achieve both low power operation and fast transient response
Solution Approach 1:
The patent implements a dynamic current mirror ratio mechanism where the ratio changes based on load conditions. A second current mirror is introduced with a larger mirror ratio than the first current mirror. A controller selectively activates either the first or second current mirror based on whether the load is light or heavy, thereby dynamically adjusting the current mirror ratio to maintain stability across different operating conditions.
2Speed
If the LDO regulator increases bandwidth to improve transient response, then transient performance improves, but power consumption increases
Solution Approach 1:
The patent dynamically adjusts the current mirror ratio based on load conditions to optimize the balance between transient response speed and power consumption. During light load conditions, the controller activates the second current mirror with the larger mirror ratio, which provides higher bandwidth and faster transient response when needed. During heavy load conditions, the first current mirror with the smaller ratio is used, reducing power consumption. This dynamic adjustment allows the regulator to achieve fast transient response only when necessary, rather than continuously operating at high bandwidth.
3Reliability
If the LDO regulator uses a larger current mirror ratio for light load stability, then stability at light load improves, but power efficiency at heavy load deteriorates
Solution Approach 1:
The patent employs a dynamic current mirror ratio adjustment mechanism that switches between two different current mirrors based on load conditions. The controller monitors the load and selectively activates the second current mirror (larger ratio) during light load conditions to ensure stability, and switches to the first current mirror (smaller ratio) during heavy load conditions to optimize power efficiency. This dynamic switching resolves the contradiction by applying the appropriate current mirror ratio only when needed.
Solution Approach 2:
The patent applies different current mirror ratios to different operating conditions. The second current mirror with the larger ratio is specifically designed for light load conditions where stability is critical, while the first current mirror with the smaller ratio is designed for heavy load conditions where power efficiency is paramount. Each current mirror is optimized for its specific operating regime, and the controller ensures the appropriate mirror is active under the corresponding load conditions.
Data Source
AI summary
A power supply circuit and techniques for voltage regulation are described. Certain aspects provide a method of supplying power by a power supply circuit. The method generally includes: generating an output voltage based on a voltage at a Vin node via a first transistor having a gate coupled to a gate of a second transistor, wherein a source of the second transistor is coupled to the Vin node and wherein a drain of the second transistor is coupled a drain of a third transistor; and sourcing a current to the third transistor, wherein during a light load condition of the power supply circuit, the current varies based on the voltage at a Vout node of the power supply circuit, and during a heavy load condition of the power supply circuit, the current is limited based on a current threshold.