Switched-Mode DC-DC Converter Ripple Control Circuit
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Solution Overview
Problem
Switched-mode DC-DC converters with large LC time constants experience multi-pulsing at the switching node, leading to improper operation and voltage ripple issues, which are difficult to address with existing ripple compensation circuits.
Innovation Solution
A modified ripple generation circuit with an increased RC time constant during the falling edge of the current sense signal CSP-CSN, achieved by splitting resistors and adding a switch in parallel, ensures that the current sense signal remains positive, preventing premature triggering of pulses and eliminating multi-pulsing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a large LC time constant is used in the DC-DC converter, then the converter can operate in skip mode at light loads, but multi-pulsing occurs at the switching node causing improper operation and voltage ripple issues
Solution Approach 1:
The patent applies preliminary anti-action by detecting the multi-pulsing condition at the switching node and preemptively adjusting the ramp signal characteristics before the multi-pulsing causes improper operation. The control circuit detects when multiple pulses occur during the off-time and modifies the ramp signal slope or offset to prevent subsequent multi-pulsing events, thereby maintaining reliable operation while preserving skip mode capability.
2Object-generated harmful factors
If existing ripple compensation circuits are used to address multi-pulsing, then voltage ripple can be reduced, but the underlying multi-pulsing issue persists and proper operation cannot be ensured
Solution Approach 1:
The patent implements feedback by continuously monitoring the switching node for multi-pulsing conditions and using this information to adjust the ramp signal characteristics. The control circuit detects when improper operation occurs due to multi-pulsing and modifies subsequent switching cycles accordingly, creating a closed-loop system that ensures proper operation while addressing voltage ripple at its root cause rather than merely compensating for its effects.
Data Source
AI summary
A circuit for controlling a switched-mode DC-DC converter. An inductor is connected between a switching node and an output node, and an output capacitor is connected in series with the inductor. An RC circuit is connected in parallel with the inductor to compensate for ripple voltage. In a discontinuous current mode, a pulse is applied to the switching node and then removed. In this mode, an RC time constant for the RC circuit is increased during the falling edge of a difference signal such that the difference signal does not drop below zero.