Linear Voltage Regulator Fast Feedback for Load Transients
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Solution Overview
Problem
Voltage regulators face challenges in maintaining stable output voltage during load transient events due to slow response times, leading to voltage overshoot or undershoot, which can result in bit error rates in high-speed applications like hard disk drives.
Innovation Solution
A linear voltage regulator with an open loop architecture and a fast feedback loop, utilizing a sense transistor and current mirror to provide a stable output voltage and rapid compensation for changes in output current, reducing timing jitter and improving turn-on time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a feedback loop is used to maintain stable output voltage, then voltage stability is improved, but response time increases causing voltage undershoot during load transients
Solution Approach 1:
The feedback system is segmented into two independent paths: a fast transient response path using a sense transistor and current mirror that operates independently of the main feedback loop, and a slower main feedback loop for steady-state regulation. The sense transistor path provides immediate response to load transients while the main loop maintains overall voltage stability.
Solution Approach 2:
The sense transistor acts as an intermediary element that senses output voltage changes and provides immediate feedback through a current mirror to the output transistor gate, bypassing the slower main feedback loop. This intermediary path enables fast transient response without compromising the stability provided by the main feedback loop.
2Reliability
If the feedback loop response time is increased to reduce voltage undershoot, then voltage stability during transients is improved, but the regulator turn-on time and overall speed decrease
Solution Approach 1:
The regulation function is segmented into transient response handling (fast path with sense transistor) and steady-state regulation (main feedback loop). This segmentation allows the transient path to operate with minimal delay while the main loop operates at optimal stability, eliminating the trade-off between response speed and stability.
Solution Approach 2:
The sense transistor and current mirror are configured to provide preliminary action during load transients by immediately responding to voltage changes before the main feedback loop can act. This preliminary response prevents voltage undershoot while maintaining fast turn-on characteristics.
3Stability of the object's composition
If a traditional feedback loop with operational amplifier is used, then voltage regulation is achieved, but output voltage ripple increases during high-speed operations
Solution Approach 1:
A fast feedback mechanism using the sense transistor and current mirror is implemented to provide immediate correction of output voltage deviations. This fast feedback path reduces output voltage ripple by responding to transients before they can propagate through the slower main feedback loop with the operational amplifier.
Solution Approach 2:
The regulator employs dynamic response characteristics through the sense transistor path that can quickly adapt to changing load conditions. This dynamic response reduces voltage ripple during high-speed operations while the main feedback loop maintains overall regulation stability.
Data Source
AI summary
In an embodiment, a linear voltage regulator includes: an output transistor having a first current path terminal configured to be coupled to a load, and a second current path terminal coupled to a first supply terminal, where the output transistor is configured to provide, at the first current path terminal, a regulated output voltage; a voltage source circuit configured to provide, in an open loop manner, a first voltage to a control terminal of the output transistor; and a feedback loop coupled between the first current path terminal of the output transistor and the control terminal of the output transistor, the feedback loop including a sense transistor having a first current path terminal coupled to the first current path terminal of the output transistor.