Switching Control Circuit for Audible Ringing Suppression
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Solution Overview
Problem
Power supply circuits generate audible ringing when the load is in a low load state due to switching frequencies within the audible frequency range, which is caused by the intermittent switching of transistors in response to fluctuations in output voltage.
Innovation Solution
A switching control circuit that includes a driver circuit, a detection circuit, and a time measurement circuit to control transistor switching, ensuring the transistor turns on when the inductor current is below a predetermined value and turns off after a specific time period, independent of the inductor current, thereby avoiding frequencies within the audible range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the transistor switching is halted to prevent output voltage from exceeding the target level in low load state, then the output voltage stability is improved, but audible ringing is produced from the coil due to switching frequency falling within the audible frequency range
Solution Approach 1:
The patent applies dynamics by making the switching control adaptive rather than fixed. The control circuit dynamically adjusts the switching frequency based on real-time detection of the transistor's on-period. When the on-period is detected to be shorter than a predetermined threshold (indicating risk of audible ringing), the control circuit actively lengthens the on-period by controlling the transistor to remain on until a predetermined time period elapses, rather than switching off immediately. This dynamic adjustment ensures the switching frequency stays above the audible range while maintaining output voltage stability.
Solution Approach 2:
The patent changes the time parameter (on-period duration) of the transistor switching based on detected conditions. By monitoring whether the on-period is shorter than a predetermined value and adjusting the transistor's on-time accordingly, the system modifies the switching frequency parameter to avoid the audible frequency range. This parameter change approach allows the system to maintain voltage stability while eliminating audible ringing by ensuring the switching frequency remains above human hearing threshold.
2Object-generated harmful factors
If the transistor switching frequency is increased to avoid audible ringing, then audible ringing is suppressed, but the complexity of the control circuit increases
Solution Approach 1:
The patent implements feedback by having the control circuit continuously monitor the transistor's on-period and use this information to adjust subsequent switching decisions. The detection circuit measures the actual on-period, compares it against a predetermined threshold, and feeds this information back to the switching control logic. This feedback mechanism enables automatic adjustment of switching frequency to avoid audible ringing without requiring complex external control systems, achieving suppression of audible ringing with relatively simple circuitry.
Solution Approach 2:
The control circuit performs self-service by autonomously detecting its own switching characteristics (on-period) and automatically adjusting its behavior to prevent audible ringing. The circuit uses its own operational parameters as the basis for control decisions, eliminating the need for external monitoring equipment or complex control systems. This self-service approach keeps the control circuit simple while effectively suppressing audible ringing through intelligent self-adjustment.
Data Source
AI summary
A switching control circuit for a power supply circuit including an inductor and a transistor. The switching control circuit switches the transistor, and includes: a driver circuit configured to turn on the transistor when an inductor current becomes smaller than a predetermined value, and turn off the transistor when a time period corresponding to an output voltage elapses; a detection circuit configured to detect whether on-period of the transistor is shorter than a first time period; and a first time measurement circuit configured to measure a second time period upon detecting that the on-period is shorter than the first time period. Upon detecting that the on-period is shorter than the first time period, the driver circuit turns on the transistor based on completion of measurement of the second time period, irrespective of the inductor current. The second time period is shorter than a period corresponding to a highest audible frequency.