DC-to-DC Power Converter Mode Control Circuit for Inaudible Operation
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Solution Overview
Problem
Power converters often produce audible noise due to switching bursts, which is undesirable in many applications, especially when operating in power saving or forced pulse width modulation modes.
Innovation Solution
A mode control circuit that generates a mode control signal with a configurable frequency and duty cycle to seamlessly transition between power save and pulse width modulation (PWM) modes, ensuring operation within an inaudible frequency range by controlling the duty cycle responsive to input signals, thereby reducing audible noise and maintaining power efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the power converter operates in power save mode with switching bursts, then power efficiency is improved, but audible noise is generated when the repetition rate exceeds audio duration
Solution Approach 1:
The patent applies periodic action by using a dither signal to modulate the duty cycle of mode control pulses, creating a periodic variation in the switching pattern. This spreads the spectral energy of the switching bursts across a wider frequency range, pushing the dominant frequencies above the audible range while maintaining the power-saving burst mode operation.
Solution Approach 2:
The patent changes the duty cycle parameter dynamically using a dither signal with frequencies above the audible range. By modulating the duty cycle at ultrasonic frequencies, the switching bursts are distributed in time and frequency domains, achieving power efficiency while eliminating audible noise through parameter variation.
2Object-generated harmful factors
If the power converter transitions between power save mode and PWM mode, then audible noise is eliminated, but power efficiency may be reduced
Solution Approach 1:
The patent applies partial action by using brief mode control pulses with duty cycles less than 50% (e.g., 1-10 microseconds). These short pulses are sufficient to transition the converter between modes and maintain inaudible operation, while minimizing the time spent in less efficient PWM mode, thus preserving overall power efficiency.
Solution Approach 2:
The patent makes the duty cycle dynamic by applying a dither signal that continuously varies the pulse width. This dynamic adjustment allows the system to adapt to changing load conditions while maintaining the switching frequency above the audible range, optimizing both noise reduction and efficiency under varying operating conditions.
3Object-generated harmful factors
If the duty cycle is configured to maintain inaudible operation, then audible noise is reduced, but control complexity increases
Solution Approach 1:
The patent introduces a dither signal as an intermediary element that simplifies the control mechanism. Instead of complex algorithms to manage mode transitions and duty cycle adjustments, a simple periodic dither signal applied to the duty cycle input automatically achieves ultrasonic frequency operation and audible noise elimination with minimal control logic.
Data Source
AI summary
In a described example, a circuit includes a mode control circuit having an input and a mode control output. The mode control output is adapted to be coupled to a mode input of a DC-to-DC power converter. The mode control circuit is configured to provide a mode control signal at the mode control output. The mode control signal has a frequency and a duty cycle for causing the power converter to operate within an inaudible frequency range by transitioning the power converter between a power save mode and a pulse width modulation (PWM) mode. The mode control circuit is configured to control the duty cycle responsive to the input of the mode control circuit.