DC Buck Converter EMI Reduction via Digital Delay-Locked Loop
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Solution Overview
Problem
Synchronous DC-DC buck converters face challenges in reducing electromagnetic interference and maintaining efficiency as switching frequency increases, particularly due to issues with dead time management and output voltage stability when applying spread spectrum clock generation techniques.
Innovation Solution
A digital delay-locked loop and spread spectrum clock are used to control switching signal waveforms, adjusting frequency and dead time to reduce electromagnetic interference while maintaining output voltage stability and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If switching frequency is increased to reduce inductor and capacitor sizes, then component size is reduced, but electromagnetic interference increases
Solution Approach 1:
The patent applies spread spectrum clock generation to dynamically vary the switching frequency around a center frequency rather than using a fixed frequency. This dynamic frequency modulation spreads the electromagnetic energy spectrum, reducing peak EMI while maintaining the high switching frequency needed for compact inductor and capacitor designs
Solution Approach 2:
The invention changes the frequency parameter of the switching signal by modulating it with a spread spectrum technique. The switching frequency is varied within a range centered at a base frequency, which transforms the concentrated electromagnetic energy into a distributed spectrum, thereby reducing EMI while preserving the benefits of high-frequency operation
2Object-affected harmful factors
If spread spectrum clock generation is applied to reduce electromagnetic interference, then electromagnetic interference is reduced, but output voltage stability deteriorates due to dead time management issues
Solution Approach 1:
The patent incorporates a feedback mechanism that monitors the switching signals and adjusts the dead time dynamically based on the spread spectrum modulation. The controller compensates for frequency variations by adjusting dead time, ensuring that the duty cycle and output voltage remain stable despite the frequency modulation used for EMI reduction
Solution Approach 2:
The invention applies preliminary compensation for dead time effects in the control algorithm. By anticipating the frequency variations introduced by spread spectrum modulation, the controller pre-adjusts the dead time parameters to maintain proper switch timing and preserve output voltage stability
3Reliability
If fixed dead time is applied to switching signals, then shoot-through current is prevented, but output voltage decreases when switching frequency is spread
Solution Approach 1:
The patent transitions from fixed dead time to dynamic dead time adjustment. The dead time is varied in proportion to the spread spectrum frequency modulation, ensuring that the minimum off-time for preventing shoot-through is maintained while allowing the effective duty cycle to be preserved across frequency variations
Solution Approach 2:
The invention changes the dead time parameter dynamically based on the instantaneous switching frequency. When frequency increases, dead time is reduced proportionally, and when frequency decreases, dead time is increased, maintaining the reliability constraint while optimizing power transfer and output voltage
Data Source
AI summary
A synchronous direct current (DC)-DC buck converter and a method of controlling the waveforms of switching signals disclosed herein. The synchronous DC-DC buck converter generates a stepped-down output voltage using a first switch configured to apply an input voltage to an inductor and a second switch configured to switch in response to a second switching signal. The synchronous DC-DC buck converter includes a sawtooth generation unit, a driver oscillating signal generation unit, a switching signal generation unit, and a phase tracking unit. The sawtooth generation unit generates a sawtooth wave. The driver oscillating signal generation unit generates an error voltage between the output voltage and a reference voltage, and compares the sawtooth wave with the error voltage, so as to generate a driver oscillating signal. The switching signal generation unit generates each of the first and second switching signals. The phase tracking unit generates the frequency setting signal.