Feedback Ramp Generator for SMPS Sub-Harmonic Suppression
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Solution Overview
Problem
Switched-mode power supplies (SMPSs) experience sub-harmonic oscillations that cause noise on the output, necessitating complex circuits and processes to mitigate these oscillations.
Innovation Solution
Control the rate of change and frequency of a ramp signal based on a feedback current mirroring the current through an energy-storage device, determining the duty cycle by comparing the ramp signal to an error signal corresponding to the output voltage of the SMPS.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If complex circuits and processes are used to prevent sub-harmonic oscillations, then sub-harmonic oscillation prevention is improved, but device complexity increases
Solution Approach 1:
The patent combines the sub-harmonic oscillation prevention function with the existing current sense circuit by having the ramp generator receive the feedback current as a direct input. This merging eliminates the need for separate complex prevention circuits while maintaining oscillation suppression through the modified ramp signal generation.
Solution Approach 2:
The feedback current from the energy-storing device serves multiple functions: it provides information for normal PWM control and simultaneously enables sub-harmonic oscillation prevention by modulating the ramp signal. This multi-functionality reduces overall system complexity while achieving reliable oscillation suppression.
2Reliability
If the duty cycle is dynamically adjusted based on feedback current, then sub-harmonic oscillation is reduced, but control complexity increases
Solution Approach 1:
The patent implements feedback by using the feedback current from the energy-storing device to dynamically adjust the ramp signal characteristics. This feedback mechanism enables automatic duty cycle modulation that suppresses sub-harmonic oscillations without requiring complex external control logic.
Solution Approach 2:
The ramp signal is made dynamic by allowing its parameters to vary with the feedback current. This dynamic adjustment enables the control system to adapt to changing operating conditions and suppress oscillations automatically, reducing the need for complex static control circuits.
Data Source
AI summary
To reduce sub-harmonic oscillations in a Switched-Mode Power Supply (SMPS). a ramp generator circuit of the SMPS produces a ramp signal having an amplitude corresponding to a sensed current through an energy storage device, such as an inductor, of the SMPS. The ramp signal is used to control a duty cycle of the SMPS. The ramp generator circuit may include a reference current circuit, a ramp capacitor, and a discharge circuit to periodically discharge the ramp capacitor. The ramp capacitor may be charged using a charging current produced by combining a feedback current corresponding to the sensed current with a reference current produced by the reference current circuit and may be periodically discharged at a fixed frequency, or may be charged using the reference current and discharged at a time determined according to the feedback current.