LDO Current Limiter Biasing for Zero No-Load Quiescent Current
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Solution Overview
Problem
Linear voltage regulators, particularly low-dropout (LDO) regulators, face inefficiencies due to quiescent current consumption even in no-load conditions, which is problematic for power-efficient applications like battery-operated devices, as this current is drawn regardless of output current levels.
Innovation Solution
A voltage regulator design that includes a current limiter circuit powered by output current, which draws zero quiescent current in no-load conditions and adjusts bias currents proportionally with output current, allowing for efficient current limiting only during heavy loads, thereby minimizing overall quiescent current consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a current limiter circuit is implemented in an LDO regulator to protect against overload conditions, then reliability is improved, but quiescent current consumption increases in no-load conditions
Solution Approach 1:
The current limiter circuit uses dynamic biasing where the bias current is proportional to the output current. When output current is zero, bias current is zero. When output current increases, bias current increases proportionally. This dynamic adjustment allows the circuit to maintain reliability while minimizing quiescent current consumption in no-load conditions.
Solution Approach 2:
The patent changes the operating parameters of the current limiter circuit by making the bias current variable rather than fixed. The bias current parameter is changed to be proportional to the output current, allowing the circuit to adapt its power consumption level based on the actual operating conditions, thus resolving the contradiction between reliability and energy use.
2Reliability
If fixed bias currents are used in the current limiter circuit to ensure proper operation during overload, then reliability is improved, but power efficiency deteriorates in no-load conditions
Solution Approach 1:
The bias current is made dynamic and proportional to the output current rather than fixed. This allows the current limiter to maintain proper operation during overload conditions while minimizing power consumption during no-load conditions, thus improving power efficiency without sacrificing reliability.
Solution Approach 2:
The current limiter circuit serves itself by using a portion of the output current to generate the necessary bias current. This self-service mechanism eliminates the need for separate fixed bias current sources, allowing the circuit to automatically adjust its power consumption based on the load conditions, thereby improving power efficiency while maintaining reliability.
Data Source
AI summary
A voltage regulator having a current limiter for over-current protection is disclosed. The current limiter is powered by a current or currents derived from an output current. In a no-load condition, in which the output current is zero, the current or currents powering the current limiter may be zero. As the output current increases, however, the current or currents powering the current limiter may grow in proportion. Thus, the current limiter can have zero quiescent current in a no-load condition but may be powered to protect the voltage regulator in a high-current condition.