DC-DC Converter Dithered Slope Compensation EMI
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Solution Overview
Problem
Fixed frequency DC-DC converters face challenges in meeting EMI compliance due to concentrated radiated emissions at harmonics of the switching frequency, which is not adequately addressed by existing techniques that modify the switching frequency in a random manner, as it affects the duty cycle and output voltage regulation.
Innovation Solution
Implementing a DC-DC converter with a control circuit that generates a ramp signal with a varying slope and duty cycle, initiated by a cycle-to-cycle varying clock signal, allowing the switching element's duty cycle and on-time to change cycle-to-cycle, thereby spreading the emitted power over a wider frequency span while maintaining proper fixed-frequency operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If the switching frequency is changed in a random manner to spread emitted power, then EMI performance is improved, but the duty cycle and output voltage regulation are affected
Solution Approach 1:
The patent applies periodic dithering action to the slope compensation signal, creating a controlled cyclic variation that spreads EMI emissions while maintaining predictable converter operation. The periodic nature of the dither signal ensures that the converter remains stable while achieving EMI compliance through frequency spreading.
Solution Approach 2:
The patent modifies the slope compensation parameter dynamically by adding a dither signal, which changes the effective switching frequency in a controlled manner. This parameter change spreads the spectral content of EMI emissions while the feedback loop maintains output voltage regulation by compensating for the frequency variations.
2Reliability
If the switching frequency is fixed to maintain proper operation, then output voltage regulation is maintained, but radiated emissions concentrate at harmonics of the switching frequency
Solution Approach 1:
By applying periodic dithering to the slope compensation, the patent creates controlled frequency variations that spread the concentrated harmonic emissions into a broader frequency spectrum, reducing peak emission levels while maintaining the fixed-frequency operational characteristics needed for stable regulation.
Solution Approach 2:
The dithered slope compensation signal acts as an intermediary that mediates between the fixed switching frequency requirement for stable operation and the need to spread EMI emissions. It introduces controlled frequency variations that achieve EMI compliance without disrupting the fundamental fixed-frequency operation mode.
3Object-affected harmful factors
If dithering is applied to spread EMI emissions, then EMI compliance is improved, but the conversion range and dynamic range for regulation may be affected
Solution Approach 1:
The patent applies partial dithering action by using a small-amplitude dither signal relative to the overall slope compensation signal. This partial action is sufficient to spread EMI emissions effectively while being too small to significantly impact the conversion range or dynamic range required for proper voltage regulation.
Solution Approach 2:
The dither signal introduces small controlled changes to the slope compensation parameter, which is sufficient to achieve EMI spectral spreading while maintaining the overall parameter ranges needed for full conversion capability and dynamic regulation response.
Data Source
AI summary
Methods and apparatus for a circuit including a DC-DC converter including: a boost converter to provide a DC voltage output from a DC input voltage, the DC output voltage configured to connect with a first load terminal, a feedback module configured to connect with a second load terminal, a switching module having a switching element coupled to the boost converter, and a control circuit coupled to the switching module to control operation of the switching element, the control circuit coupled to the feedback module, wherein the control circuit includes a slope generator to generate a ramp signal having a slope that can vary cycle to cycle.