Switched Converter Feedback Synchronization for Loop Stability
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Solution Overview
Problem
Conventional analog control methods for switched power converters, particularly in current mode control, face instability due to race conditions caused by the drift in the time base of the voltage feedback signal relative to the PWM signal, leading to potential instability in the loop.
Innovation Solution
The implementation of a synchronizer circuit that utilizes leading edge blanking (LEB) to condition the peak current feedback signal, ensuring it transitions only after the PWM output has stabilized, thereby preventing premature triggering and maintaining loop stability by synchronizing the feedback and PWM signals within a defined timing window.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional analog control methods are used for current mode control, then the converter can regulate output current by monitoring inductor current, but the time base of the voltage feedback signal may drift away from the PWM signal time base causing race conditions and loop instability
Solution Approach 1:
The synchronizer circuit performs preliminary synchronization of the feedback signal time base with the PWM signal time base before the feedback signal is used for control decisions. This preliminary alignment prevents time base drift from causing race conditions, ensuring that the feedback signal transitions occur at the correct timing relative to the PWM signal edges.
Solution Approach 2:
The synchronizer circuit acts as an intermediary between the voltage feedback signal path and the PWM signal path. It mediates the timing relationship between these two signals by adjusting the feedback signal's time base to match the PWM signal, thereby preventing direct interaction that would cause race conditions while maintaining the necessary feedback control function.
2Device complexity
If the voltage feedback signal transitions in response to PWM output signal without synchronization, then the control loop can operate with simple circuitry, but race conditions may occur causing instability
Solution Approach 1:
The synchronizer circuit performs preliminary synchronization of the feedback signal time base with the PWM signal time base before the feedback signal is used for control decisions. This preliminary alignment prevents time base drift from causing race conditions, ensuring that the feedback signal transitions occur at the correct timing relative to the PWM signal edges.
Solution Approach 2:
The synchronizer circuit acts as an intermediary between the voltage feedback signal path and the PWM signal path. It mediates the timing relationship between these two signals by adjusting the feedback signal's time base to match the PWM signal, thereby preventing direct interaction that would cause race conditions while maintaining the necessary feedback control function.
Data Source
AI summary
A device includes a switched power converter with an inductor, the power converter to produce a voltage output based on a pulse-width modulated (PWM) signal, and produce a peak current feedback signal, the peak current feedback signal representative of a peak current through the inductor. The device includes a comparator to generate a PWM control input (PCI) signal based on whether the peak current feedback signal has reached a reference current. The device includes a PWM generation circuit to generate the PWM signal to control switching of the switched power converter based on the PCI signal. The device includes a synchronization circuit to delay a change in the PCI signal.