SMPS Controller Circuit Reducing Transient Undervoltage
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Solution Overview
Problem
Switched-Mode Power Supplies (SMPS) experience undervoltage during transient conditions due to the transition between Pulse Frequency Modulation (PFM) and Pulse Width Modulation (PWM) control loops, leading to loss of control and undesirable voltage regulation.
Innovation Solution
A controller circuit generates a shift signal based on the voltage difference between a reference and feedback voltage to drive the selection of control loops, shifting the PWM compensation range and ensuring closed-loop operation during load changes, thereby reducing the gap between PFM and PWM control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the controller circuit operates in open loop control during transient conditions, then the controller can respond quickly to load changes, but undervoltage occurs due to loss of control loop regulation
Solution Approach 1:
The controller circuit predicts the transient condition and preemptively switches from PFM to PWM control mode before the actual load change occurs. This preliminary action maintains closed-loop regulation during the transition, preventing undervoltage while ensuring quick response to load changes
2Loss of energy
If the controller circuit uses PFM control loop, then efficiency is improved during light loading, but control loop separation causes transient undervoltage when switching to PWM
Solution Approach 1:
The controller merges the PFM and PWM control loops into a unified control structure where the PWM loop encompasses the PFM functionality. This merging eliminates the control gap during transitions by ensuring continuous closed-loop regulation regardless of which mode is active, while maintaining efficiency benefits of PFM during light loading
3Loss of energy
If the controller circuit delays switching from PFM to PWM control loop, then efficiency is maintained during light loading, but transient response time increases causing undervoltage
Solution Approach 1:
The controller detects the onset of transient conditions and preemptively switches from PFM to PWM mode before the full load change occurs. This preliminary switching action reduces transient response time and prevents undervoltage, while the controller returns to PFM mode after the transient settles, maintaining efficiency during normal light loading operation
Data Source
AI summary
A controller circuit for generating a Pulse-Width Modulation (PWM) signal for activating a switching device of a Switched-Mode Power Supply (SMPS) includes gap detection circuitry, Pulse Frequency Modulated (PFM) circuitry, PWM circuitry and logic circuitry. The gap detection circuitry is configured to generate a shift signal based on an indication of a voltage difference between a reference voltage and a feedback voltage corresponding to voltage output by the SMPS. The PFM circuitry is configured to generate a hold signal indicating a target PFM frequency for the PWM signal. The PWM circuitry is configured to shift, based on the shift signal, a pedestal current to generate a shifted pedestal current and to generate, based on the shifted pedestal current, a peak signal indicating a target PWM on time for the PWM signal.