Cycle Skipping Prevent Circuit for DC-DC Converter Noise Reduction
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Solution Overview
Problem
DC-to-DC converters employing peak and valley current mode control often experience cycle skipping issues due to sudden changes in load, leading to undesirable noise generation in the AM frequency band, particularly in automotive applications.
Innovation Solution
A cycle skipping prevent circuit is introduced, which includes a latch, comparator, and oscillator circuit, ensuring the latch is reset or set at regular intervals by gating signals based on the transition of error and compensated error voltage signals, thereby preventing cycle skipping and minimizing noise generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If peak or valley current mode control is used in DC-to-DC converters, then the converter can efficiently regulate voltage, but cycle skipping occurs during sudden load changes causing noise in the AM frequency band
Solution Approach 1:
The oscillator circuit generates a periodic signal that preemptively triggers the latch to reset or set at regular intervals, preventing cycle skipping before it can occur during load transitions. This preliminary action ensures continuous switching cycles even when load conditions would normally cause the converter to skip cycles.
Solution Approach 2:
The oscillator circuit provides a periodic trigger signal that forces the latch to transition at regular intervals, creating a consistent switching rhythm. This periodic action overrides the irregular switching patterns that cause cycle skipping and associated noise, maintaining stable operation during load changes.
2Adaptability or versatility
If the latch is allowed to skip cycles during load changes, then the converter adapts to load conditions, but undesirable noise is generated in the AM frequency band
Solution Approach 1:
The comparator circuit continuously monitors the relationship between the current sense voltage and compensated error voltage, providing feedback that triggers the latch to reset or set. This feedback mechanism ensures the converter responds appropriately to load conditions while maintaining regular switching cycles through the oscillator's periodic influence, preventing noise-generating cycle skipping.
3Reliability
If the oscillator signal has a small duty cycle with constant frequency, then cycle skipping is prevented, but the circuit complexity increases
Solution Approach 1:
The oscillator, comparator, and latch are integrated into a unified control circuit where the oscillator's periodic signal combines with the comparator's feedback signal to control the latch. This merging of functions achieves reliable cycle skipping prevention while minimizing circuit complexity through shared components and coordinated operation.
Data Source
AI summary
A DC-to-DC converter employs peak current mode control and includes a cycle skipping prevent circuit. If a latch is set, then a high side switch is turned on. A comparator receives a signal indicative of current flow and a compensated error signal. The prevent circuit supplies a delayed version of a low duty cycle, fixed frequency, oscillator signal onto the set input lead of the latch. The prevent circuit gates a high signal as output by the comparator onto the reset input lead of the latch. If the output of the comparator has, however, not transitioned high by a predetermined time, then the prevent circuit gates a high pulse onto the reset input lead. Accordingly, the prevent circuit ensures that the latch is reset once every period of the signal SET. A cycle skipping prevent circuit is also disclosed for use in a converter that employs valley current mode control.