Switching Regulator Adaptive On-Time Control
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Solution Overview
Problem
Switching regulators face challenges in maintaining a substantially constant switching frequency while providing fast transient response, which can lead to electromagnetic interference (EMI) and noise issues.
Innovation Solution
The solution involves a method and apparatus that include a comparison circuit, a one-shot circuit, and a pulse duration controller to regulate the switching frequency, using a feedback signal and a reference signal to control the duration of switch control pulses, with optional frequency jittering and scaling circuitry to manage EMI.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If pulse frequency modulation (PFM) is used to achieve fast transient response, then transient response speed is improved, but switching frequency becomes variable which complicates EMI filtering
Solution Approach 1:
The patent implements a hybrid control system that dynamically switches between PFM and PWM modes based on operating conditions. The controller monitors the error signal amplitude and transitions from PFM (for fast response during large transients) to PWM (for stable frequency during normal operation), thereby achieving fast transient response while maintaining constant switching frequency to simplify EMI filtering.
2Device complexity
If pulse width modulation (PWM) is used to maintain constant switching frequency, then EMI filtering is simplified, but transient response becomes slower
Solution Approach 1:
The hybrid control system dynamically adjusts the modulation mode based on transient conditions. During normal operation, PWM mode maintains constant switching frequency for simplified EMI filtering. When a transient event is detected (large error signal), the system dynamically switches to PFM mode to provide fast response, then returns to PWM mode after the transient settles, thus combining the advantages of both modes.
Solution Approach 2:
The patent changes the control parameter (modulation mode) based on operating conditions. The controller monitors error signal characteristics and adjusts the modulation strategy accordingly - using PWM with fixed duty cycle adjustments for normal operation and PFM with variable pulse frequencies for transient conditions, thereby optimizing both EMI performance and transient response.
3Speed
If PFM switching regulator is used to provide fast transient response, then transient response is improved, but electromagnetic interference (EMI) and switching noise are generated at variable frequencies
Solution Approach 1:
The hybrid control system dynamically selects the appropriate modulation mode based on transient severity. During normal operation, PWM mode maintains constant switching frequency, confining EMI and switching noise to predictable frequencies that are easier to filter. During transients, PFM mode provides fast response despite variable frequency noise, but only for the brief duration necessary to correct the transient condition.
Data Source
AI summary
The invention relates to a method and an apparatus for maintaining a substantially constant switching frequency in a relatively fast transient response switching regulator. The apparatus includes a comparison circuit, a one-shot circuit, and a pulse duration controller. The comparison circuit provides a comparison signal to the one-shot circuit based on a comparison of a feedback signal and a reference signal. The one-shot circuit provides a configured duration switch control pulse when the comparison signal is asserted. The pulse duration controller controls the configured duration of the switch control pulse (e.g., duration of a pulse on-time or off-time) to affect the switching frequency of the regulator. In addition, frequency jittering and frequency scaling circuitry may be included.