Intermittent Oscillation Frequency Control for Switching Power Supply Noise Reduction
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Solution Overview
Problem
Conventional switching power supply apparatuses face challenges in reducing audio noises generated by transformers and capacitors during intermittent oscillation under light loads, as existing techniques either compromise power efficiency or increase costs.
Innovation Solution
A semiconductor device with an intermittent-oscillation frequency control circuit that delays the switching state changes to ensure the intermittence period falls outside a specific audible frequency range, using timers and external capacitors to set measurement periods, allowing for flexible control of switching frequencies and reducing noise generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If intermittent-oscillation control is used under light load to improve power efficiency, then power consumption is reduced, but audio noises are generated when switching frequency falls within audible range
Solution Approach 1:
The patent changes the switching frequency parameter dynamically by introducing an intermittence control period that delays the start of intermittent oscillation. This frequency modulation moves the operating frequency out of the audible range (20Hz-20kHz) while maintaining the power efficiency benefits of intermittent-oscillation control under light load conditions
Solution Approach 2:
The patent implements a periodic delay mechanism where the intermittence control circuit introduces a controllable delay period before initiating intermittent oscillation. This periodic action structure allows the system to operate at frequencies below the audible range while still achieving the power savings of intermittent control
2Object-generated harmful factors
If peak current of switching element is decreased to reduce transformer noises, then audio noises are reduced, but number of switching cycles increases resulting in worse power efficiency
Solution Approach 1:
Instead of changing the peak current parameter, the patent changes the frequency parameter by introducing a delay period. This approach reduces noises by lowering the switching frequency below audible ranges while maintaining adequate peak current levels to limit the number of switching cycles and preserve power efficiency
3Object-generated harmful factors
If bonding or impregnating of transformers is performed to reduce noises, then audio noises are reduced, but manufacturing cost increases
Solution Approach 1:
The patent replaces mechanical/physical noise reduction methods (bonding or impregnating) with an electronic control method. By using an intermittence control circuit to modulate the switching frequency, the system achieves noise reduction through electrical parameter control rather than physical transformer modifications, thereby reducing manufacturing costs
Data Source
AI summary
A semiconductor device providing a control circuit for controlling a switching power supply apparatus includes: an intermittent-oscillation control circuit which outputs an enable signal providing instructions to execute and suspend switching alternately; a turn-on control circuit which changes between an execution state and a suspension state of the switching according to the enable signal, and outputs, only in the execution state, a turn-on signal which turns on the switching element with a switching period; and an intermittent-oscillation frequency control circuit which causes the turn-on control circuit to delay the changing between the execution state and the suspension state so that an intermittence period including periods during which the turn-on control circuit is in the execution state and the turn-on control circuit is in the suspension state falls outside of a specific time range. Intermittent oscillation is thus operated out of a specific frequency band within an audible frequency range.