Switching Power Supply Control Circuit for Audible Noise Suppression
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Solution Overview
Problem
Switching power supply apparatuses with control circuits and blanking functions can generate sounds under light load due to a shorter blanking period, leading to irregular duty cycle changes and potential audible noise.
Innovation Solution
A control circuit with a comparator that compares the current flowing through a switching element and adjusts the comparison signal based on a blanking pulse signal, ensuring the switching element remains on for a predetermined period, thereby stabilizing the duty cycle and preventing sound generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the blanking period is shortened to improve productivity under light load, then the switching frequency increases, but sound generation occurs due to irregular duty cycle changes
Solution Approach 1:
The patent applies preliminary anti-action by introducing a blanking pulse signal that preemptively prevents the comparison signal from becoming active during the blanking period. This preliminary action ensures that the switching element cannot be turned off during this interval, thereby preventing the irregular duty cycle changes that would cause audible noise under light load conditions
Solution Approach 2:
The patent implements preliminary action by establishing a predetermined blanking period before normal PWM operation begins. During this period, the blanking pulse signal is generated in advance to ensure the switching element remains on, preventing premature turn-off and the resulting audible noise that would occur with shortened blanking periods
2Object-generated harmful factors
If the blanking period is extended to prevent sound generation, then the switching frequency decreases, but productivity is reduced
Solution Approach 1:
The patent applies dynamics by making the blanking period adaptive rather than fixed. The blanking period is dynamically adjusted based on the relationship between switching frequency and audible noise frequencies, allowing the system to maintain noise suppression while optimizing switching frequency for productivity. This dynamic adjustment enables the blanking period to be shortened when it won't cause audible noise, thereby maintaining higher switching frequencies
3Productivity
If the blanking period is made variable to optimize productivity, then the switching frequency increases, but the duty cycle becomes irregular leading to sound generation
Solution Approach 1:
The patent implements feedback by continuously monitoring the switching frequency and adjusting the blanking period accordingly. The control circuit uses feedback to ensure that the blanking period maintains a predetermined relationship with the switching frequency, preventing irregular duty cycle changes that would cause audible noise while allowing productivity-optimizing frequency adjustments
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 suppresses sound generation under light load by maintaining a consistent duty cycle, ensuring the switching element is turned off only when necessary, thus preventing audible noise.
Implementation Method 1
a comparator for comparing a voltage corresponding to a current flowing through a switching element in the switching power supply apparatus with a voltage to be compared therewith, and outputting a comparison signal corresponding to a result of the comparison
Implementation Method 2
the blanking pulse signal indicates whether or not it is currently in a predetermined period that is set for ensuring that the switching element is not turned off for the predetermined period after the switching element has been turned on
Implementation Method 3
The direct current converted by such full-wave rectification is smoothed by a capacitor C1, and then supplied to the series circuit of a primary-side winding Tn1 of an output transformer T1 and a switching element PT1
Implementation Method 4
This pulsating current is rectified by a diode D2 and smoothed by a capacitor C3, thereby converted into a direct current
Implementation Method 5
The direct current converted by such full-wave rectification is smoothed by a capacitor C1
Data Source
AI summary
A control circuit 2a for a switching power supply apparatus includes a comparator COMPa for comparing a voltage corresponding to a current flowing through a switching element PT1 with a voltage to be compared therewith, and outputting a comparison signal corresponding to a result of the comparison. To the comparator, a blanking pulse signal is also input. Here, the blanking pulse signal indicates whether or not it is currently in a predetermined period that is set for ensuring that the switching element is not turned off for the predetermined period after the switching element has been turned on. When the blanking pulse signal indicates that it is currently in the predetermined period, the comparison signal is set to low level independently of the voltage corresponding to the current and the voltage to be compared therewith.