LDO Regulator NMOS Current Buffer Speed
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Solution Overview
Problem
Low drop-out voltage regulators face issues with voltage fluctuations due to the slow response of P-channel MOS transistors to changes in load current, requiring large output capacitors that increase manufacturing costs.
Innovation Solution
Incorporating a current regulating means, such as an N-channel MOS transistor, connected to the pass device and controlled by a comparator to maintain a constant current through the pass device, regardless of load current variations, using resistance means to regulate the current based on voltage drops across a shunt resistor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a P-channel MOS transistor is used as the pass device in an LDO voltage regulator, then the device can provide the required voltage level to the load, but the response time to changes in load current becomes slow
Solution Approach 1:
The patent divides the current regulation function into two separate paths: a main current path through the PMOS pass device for steady-state regulation, and a fast response current path through an NMOS transistor for rapid load current changes. This segmentation allows each transistor to be optimized for its specific function, resolving the contradiction between stability and speed.
Solution Approach 2:
The patent introduces an NMOS transistor as an intermediary device that acts as a current buffer between the supply and the load. This NMOS transistor responds rapidly to load current changes and compensates for the slow response of the PMOS pass device, thereby improving overall response time without sacrificing voltage regulation stability.
2Stability of the object's composition
If a large output capacitor is added to minimize voltage fluctuations, then the voltage stability improves, but the manufacturing cost increases due to additional discrete components
Solution Approach 1:
The patent extracts the voltage stabilization function from the external output capacitor and implements it internally using the NMOS transistor as a current buffer. By taking out this function from an external discrete component and integrating it into the circuit using active devices, the patent eliminates the need for large capacitors while maintaining voltage stability.
Solution Approach 2:
The patent replaces the passive mechanical/electrical system (large output capacitor) with an active electronic system (NMOS transistor-based current regulation). This substitution allows voltage stability to be achieved through active current control rather than passive energy storage, reducing component count and manufacturing cost.
Data Source
AI summary
A low drop-out DC voltage regulator regulates a voltage from a DC supply and includes: a pass device controllable to maintain a voltage at an output of the regulator and arranged to provide a first current from the DC supply, at least part of said first current being provided to a load coupled to the output of the regulator; and a current regulator coupled to said pass device and to the output of the regulator. The current regulator is arranged to conduct a second current controllable such that the first current through said pass device remains constant irrespective of variations in a load current to said load.