LDO Regulator Startup Control for High PSRR and Smooth Output
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing low dropout linear regulators with high power supply rejection ratio suffer from sudden changes in output voltage during the startup process of N-type MOSFETs, leading to increased instantaneous current and potential damage to the power transistor and load, which compromises circuit stability.
Innovation Solution
The proposed low dropout linear regulator incorporates a dual-input stage error amplifier with a cascode amplifier stage and a control circuit, utilizing P-type and N-type MOSFETs in alternating pairs to control the turn-on and turn-off states of the first input stage based on a reference voltage, ensuring smooth output voltage changes and maintaining high power supply rejection ratio.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If N-type MOSFETs are used in the input stage of the error amplifier to achieve high power supply rejection ratio, then the power supply rejection ratio is improved, but the output voltage experiences sudden changes during startup, causing increased instantaneous current and potential damage to the power transistor and load
Solution Approach 1:
The control circuit activates the first input stage before the second input stage during startup. This preliminary action allows the error amplifier to gradually establish output voltage without sudden changes, preventing instantaneous current spikes while maintaining the high power supply rejection ratio provided by the N-type MOSFETs in the second input stage
Solution Approach 2:
The patent dynamically controls the activation state of the first input stage based on the startup phase. During startup, the control circuit enables the first input stage to provide gradual voltage establishment, then switches to the second input stage for normal operation, creating a dynamic transition that resolves the contradiction between startup stability and power supply rejection ratio
Data Source
AI summary
Disclosed is a low dropout linear regulator including a power transistor and an error amplifier having a first input stage, a second input stage and a control circuit. The first input stage includes a first pair of transistors receiving an output voltage and a reference voltage, the second input stage includes a second pair of transistors receiving the output voltage and the reference voltage, the first and second pairs of transistors have different conductivity types. The control circuit controls turn-on and turn-off states of the first input stage according to the reference voltage, and turns on the first input stage when the reference voltage is less than a preset threshold, so that the error amplifier operates normally and the output voltage changes smoothly. When the reference voltage is greater than the preset threshold, the control circuit turns off the first input stage so that only the second input stage operates.