DC/DC Converter Light Load Noise Suppression
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Solution Overview
Problem
DC/DC converters in consumer electronics generate unpleasant acoustic noise, known as 'mosquito noise,' due to reduced switching frequency in light load states, which affects efficiency and user experience.
Innovation Solution
A control circuit for DC/DC converters that includes a second oscillator generating a cyclic signal with a longer period, allowing the switching transistor to operate at a set frequency, even in light load states, thereby suppressing acoustic noise by maintaining a consistent switching frequency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the switching frequency is reduced in light load states to improve efficiency, then energy consumption decreases, but acoustic noise increases
Solution Approach 1:
The patent applies periodic action by using a second oscillator to generate cyclic signals that periodically turn on the switching transistor during light load states. Instead of continuous low-frequency switching that causes mosquito noise, the system uses periodic bursts of switching activity synchronized with the second oscillator's cyclic signal, maintaining efficiency while eliminating audible noise frequencies.
Solution Approach 2:
The patent changes the switching frequency parameter dynamically based on load conditions. In light load states, instead of maintaining a fixed low frequency that causes noise, the system transitions to a different operational mode where the switching frequency is modulated by the second oscillator's cyclic signal, changing the frequency characteristics to avoid the mosquito noise range while maintaining energy efficiency.
2Use of energy by moving object
If the switching frequency is reduced in light load states, then efficiency improves, but switching frequency consistency deteriorates
Solution Approach 1:
The patent applies dynamics by making the switching frequency adaptive rather than fixed. The control circuit dynamically adjusts the switching frequency based on the second oscillator's cyclic signal, allowing the system to optimize efficiency in light load states while maintaining controlled frequency variation. This dynamic adjustment prevents the inconsistency and noise associated with fixed low-frequency operation.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces unwanted acoustic noise by maintaining a consistent switching frequency, improving efficiency and user experience, even in light load conditions.
Implementation Method 1
a switching transistor M1 and a primary winding W1. A pulse modulator 110 is configured to generate a pulse modulation signal SPM having a duty ratio which is adjusted according to a feedback voltage Vfb
Implementation Method 2
A phototransistor (or otherwise a photodiode) of the photocoupler 214 is configured to convert a light signal S12 received from the light-emitting diode into the feedback voltage Vfb that corresponds to the feedback signal S11
Data Source
AI summary
A pulse modulator generates a pulse modulation signal SPM having a duty ratio which is adjusted according to a feedback voltage Vfb that corresponds to the output voltage VOUT of a DC/DC converter. A second oscillator generates a second cyclic signal which is asserted with each of a predetermined second period. A light load detection circuit generates a light load detection signal which is asserted when the feedback voltage Vfb becomes lower than a first threshold voltage. A driving circuit drives a switching transistor according to the pulse modulation signal SPM. Furthermore, the driving circuit suspends the driving of the switching transistor during a period until the second cyclic signal is next asserted after the light load detection signal is asserted.