DC/DC Converter Noise Suppression via Variable Frequency Control
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Solution Overview
Problem
DC/DC converters in electronic devices face noise issues due to switching frequency entering the audible band, particularly when using ceramic capacitors, which can generate acoustic noise, despite efficiency improvements in light load states.
Innovation Solution
A control circuit for DC/DC converters that adjusts the switching frequency by varying the timing of operational states, including an on state, off state, and high impedance state, using a switching controller with components like a timer and frequency controller to modulate the switching frequency and reduce noise through spectrum spreading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the switching frequency is increased to improve efficiency in light load states, then efficiency is improved, but acoustic noise is generated when the frequency enters the audible band
Solution Approach 1:
The patent applies dynamics by making the switching frequency variable rather than fixed. The control circuit dynamically adjusts the switching frequency based on the operating state, transitioning from a fixed high frequency (which causes noise) to a variable frequency that adapts to load conditions, thereby avoiding the audible band while maintaining efficiency.
Solution Approach 2:
The patent employs periodic action through frequency modulation where the switching frequency is varied periodically or randomly within a range. This periodic variation prevents the switching frequency from settling at a constant value within the audible band, thereby suppressing acoustic noise while maintaining overall efficiency through optimized switching cycles.
2Object-generated harmful factors
If the switching frequency is decreased to avoid acoustic noise, then noise is suppressed, but efficiency deteriorates in light load states
Solution Approach 1:
The control circuit dynamically adapts the switching frequency based on real-time operating conditions. In light load states, it can operate at higher frequencies for efficiency, while in other states it adjusts to lower frequencies to avoid noise, thus dynamically optimizing both efficiency and noise suppression.
Solution Approach 2:
The patent changes the switching frequency parameter dynamically rather than maintaining a fixed value. By modulating this critical parameter based on operating state, the system achieves both high efficiency when needed and noise suppression when the frequency would otherwise enter the audible band.
3Device complexity
If a fixed switching frequency is used to simplify control, then control complexity is reduced, but noise suppression capability is lost
Solution Approach 1:
The control circuit implements dynamic frequency adjustment through a relatively simple mechanism that monitors operating state and modulates the switching frequency accordingly. This dynamic approach provides noise suppression capability while maintaining acceptable control complexity through efficient state-based decision logic.
Solution Approach 2:
The patent modifies the switching frequency parameter based on operating conditions using a control circuit that, while more complex than fixed-frequency control, remains practical through standardized implementation. The parameter change capability enables noise suppression while the control complexity is managed through efficient circuit design and state-based control logic.
Data Source
AI summary
A control circuit of a DC/DC converter includes: a driver turning on a switching transistor and turning off a rectifying transistor in on state, turning off the switching transistor and turning on the rectifying transistor in off state, and turning off the switching transistor and turning off the rectifying transistor in high impedance state; and a switching controller controlling the on state, the off state and the high impedance state, wherein the switching controller repeats a process including: transitioning to the off state when predetermined condition is satisfied in the on state; transitioning to the high impedance state with zero-cross of coil current flowing into an inductor as trigger in the off state; measuring variable time per cycle and transitioning to the off state with time-up as trigger; and transitioning to the on state when feedback voltage corresponding to output voltage of the DC/DC converter decreases to lower threshold voltage.