Voltage Regulator Fast Load Transient Response
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Solution Overview
Problem
Voltage regulators face challenges in responding rapidly to abrupt load transients, particularly undervoltage conditions when load changes from light to heavy, due to slow transient response and large gate capacitance of output transistors, which limits current supply and feedback loop stability.
Innovation Solution
Incorporating an undervoltage detector and overvoltage detector with a charge transistor and discharge transistor, respectively, to rapidly compensate for undervoltage and overvoltage conditions, utilizing a smaller charge transistor with a blocking device to speed up the response and a low-pass filter for overvoltage detection, allowing for faster compensation of output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the output transistor is made large to supply sufficient current, then the current supply capability is improved, but the gate capacitance increases resulting in slower response speed
Solution Approach 1:
The patent divides the single output transistor into two separate transistors: a main output transistor (Q1) for normal current supply and a fast response transistor (Q2) for rapid transient response. This segmentation allows each transistor to be optimized for its specific function - Q1 can be large for current capacity while Q2 can be small for fast switching, resolving the contradiction between current supply capability and response speed.
Solution Approach 2:
The patent implements dynamic switching between transistors based on load conditions. The control circuit monitors the error amplifier output and dynamically activates Q2 during transient conditions (when error amplifier output exceeds threshold) and deactivates it during steady-state operation. This dynamic behavior allows the system to achieve fast response when needed while maintaining efficient normal operation.
2Power
If the feedback loop path is used to pull up the gate voltage of the output transistor, then the current supply is improved, but the transient response becomes slow due to compensation stability requirements
Solution Approach 1:
The patent introduces a control circuit as an intermediary between the feedback loop and the fast response transistor. This control circuit includes a threshold detector that monitors the error amplifier output and triggers Q2 activation only when undervoltage conditions are detected. The intermediary control circuit allows the system to bypass the slow feedback loop compensation mechanism during transients by directly controlling Q2 based on threshold comparison, achieving fast response without compromising stability.
Solution Approach 2:
The patent replaces the gradual, continuous adjustment mechanism of the feedback loop with a discrete, threshold-based triggering mechanism. Instead of relying on the slow, continuous voltage division and amplification through the feedback network, the system uses a comparator-like threshold detection that instantly activates Q2 when the error amplifier output exceeds the threshold voltage, substituting the mechanical/continuous feedback process with an electronic threshold-triggered response.
3Speed
If an added buffer stage with increased bias current is used to speed up the output transistor response, then the response speed is improved, but the current consumption increases and feedback loop delay remains
Solution Approach 1:
The patent implements periodic or conditional activation of the fast response transistor rather than continuous operation. The control circuit monitors the error amplifier output and only activates Q2 during transient undervoltage conditions (when the output voltage drops below the threshold). During normal steady-state operation, Q2 remains off, consuming no additional bias current. This periodic/conditional action achieves fast response when needed while avoiding the continuous current consumption penalty of a permanently active buffer stage.
Solution Approach 2:
The patent changes the operating parameters of the transistor system dynamically. The fast response transistor Q2 is activated only when specific voltage threshold conditions are met (error amplifier output exceeds threshold voltage), changing the system's effective parameters from single-transistor mode to dual-transistor mode. This parameter-based switching allows the system to achieve enhanced performance (fast response) only when necessary, rather than maintaining high-performance parameters continuously, thus avoiding excessive current consumption.
Data Source
AI summary
A voltage regulator includes an undervoltage detector having a charge transistor smaller than an output transistor of the voltage regulator, providing a detection path for fast response, compensating undervoltage without large control current when loading changes from light to heavy.