Hysteretic Boost Converter Timing Control for Schottky Diode Stability
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Solution Overview
Problem
Conventional hysteretic current-mode boost converters become unstable when external Schottky diodes are used, as the inductor current cannot be accurately sensed, leading to oscillations and variability in output voltage and frequency.
Innovation Solution
The proposed solution involves controlling the timing of the converter by generating constant off times, using a timing controller that selects between off times generated by both the hysteretic current comparator and a timing generator, ensuring stable operation regardless of the presence of an external Schottky diode, by seamlessly adapting to maintain a stable output voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If external Schottky diodes are used in hysteretic current-mode boost converters, then output current capability is increased, but converter stability deteriorates due to inaccurate inductor current sensing
Solution Approach 1:
The patent introduces a timing controller as an intermediary component that mediates between the hysteretic current comparator and the PWM generator. This timing controller generates constant off-time signals that override the hysteretic control when external Schottky diodes are detected, preventing the stability issues caused by inaccurate current sensing while allowing the Schottky diodes to remain in the circuit for enhanced output current capability
Solution Approach 2:
The patent changes the control parameter from hysteretic current-based timing to constant off-time control when external Schottky diodes are present. By detecting the presence of external diodes and switching to a different control mode with fixed off-time periods, the system maintains stability while preserving the ability to use Schottky diodes for increased power output
2Loss of energy
If hysteretic current control mode is used, then converter efficiency is improved, but output voltage stability deteriorates when external Schottky diodes are present
Solution Approach 1:
The patent implements a dynamic control system that adapts its operation mode based on the presence of external Schottky diodes. The timing controller dynamically switches between hysteretic current-mode control (for efficiency) and constant off-time control (for stability), allowing the system to optimize performance characteristics based on operating conditions and component configuration
3Device complexity
If inductor current sensing is performed in conventional manner, then current control is simplified, but measurement accuracy deteriorates when external Schottky diodes are used
Solution Approach 1:
The patent extracts the timing control function from the current sensing path by introducing a separate timing controller that generates constant off-time signals independently of the current sensing accuracy. This separation allows the current sensing to remain simple while the timing control ensures accurate switching regardless of current measurement errors caused by external Schottky diodes
Data Source
AI summary
Examples to control timing for current-mode boost converters are disclosed. An example device to control timing includes a first input terminal to receive an input voltage of a current-mode boost converter a second input terminal to receive an output voltage of the current-mode boost converter, a generator to generate a first timing signal from the input voltage and the output voltage, a third input terminal to receive a second timing signal from the current-mode boost converter, a selector to select between the first on_off time signal and the second on_off time signal to generate a third on_off time signal based on a comparison of a first off time duration of the first on_off time signal and a second off time duration of the second on_off time signal, and an output terminal to control off times of the current-mode boost converter based on the third on_off time signal.