Power Supply Control Circuit With Variable Switching Frequency for EMI
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Solution Overview
Problem
Existing power supply devices face issues with electromagnetic interference (EMI) due to fixed switching frequencies, leading to quasi-peak (QP) values exceeding standard limits during testing, and require additional circuit elements like common-mode inductors, which increase cost and copper loss.
Innovation Solution
A power supply device with a control circuit that includes a frequency perturbation module and a frequency setting module, dynamically varying the switching frequency of switching elements based on perturbation and basic signals at different frequencies, dispersing EMI without increasing inductance or coil count.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a fixed switching frequency is used in the control circuit, then the power conversion efficiency is maintained, but the electromagnetic interference (EMI) quasi-peak value exceeds the standard limited value
Solution Approach 1:
The patent applies dynamics by transitioning from a fixed switching frequency to a varying switching frequency. The frequency setting module dynamically adjusts the switching frequency of the switching element based on feedback from the EMI detection module, allowing the system to adapt its operating frequency to minimize EMI emissions while maintaining power conversion efficiency.
Solution Approach 2:
The patent changes the frequency parameter of the switching element from a constant value to a variable value. The control circuit modifies the switching frequency parameter in real-time based on EMI measurements, thereby reducing the quasi-peak EMI values to comply with standards without sacrificing conversion efficiency.
2Object-generated harmful factors
If additional filtering elements are added to reduce EMI, then the EMI quasi-peak value decreases, but the copper loss increases and power efficiency decreases
Solution Approach 1:
The patent converts the harmful EMI phenomenon into a useful control signal. By detecting EMI emissions and using them to modulate the switching frequency, the system turns the problematic EMI into a feedback mechanism that actively reduces emissions, eliminating the need for additional filtering elements that would cause copper loss.
Solution Approach 2:
Instead of adding physical filtering components that increase copper loss, the patent changes the operational parameter (switching frequency) to achieve EMI reduction. This parameter-based solution avoids the energy losses associated with additional inductors, capacitors, and resistors while still meeting EMI standards.
3Object-generated harmful factors
If additional filtering elements are added to reduce EMI, then the EMI quasi-peak value decreases, but the device complexity and cost increase
Solution Approach 1:
The patent repurposes the EMI signal itself as a feedback input for frequency control, converting a harmful emission into a useful control parameter. This approach eliminates the need for additional filtering components, reducing device complexity and cost while effectively managing EMI.
Solution Approach 2:
The system performs EMI reduction through self-regulation. The EMI detection module monitors the system's own emissions, and the frequency setting module automatically adjusts the switching frequency in response, creating a self-correcting mechanism that reduces EMI without external filtering components.
Data Source
AI summary
A power supply device includes a rectification circuit, a regulation circuit, a power conversion circuit and a control circuit. The rectification circuit rectifies an input power having a first frequency. The regulation circuit regulates the input power by a switching element. The control circuit includes a controller, a frequency perturbation module and a frequency setting module. The controller controls the switching element according to a control signal. The frequency perturbation module drains the input power to generate a perturbation signal having the first frequency. The frequency setting module generates the control signal based on a basic signal and a perturbation signal having a second frequency. Accordingly, the perturbation signal and the basic signal operating at different frequencies enable the control signal to operate at a varying frequency, further enabling a switching operation of the switching element to operate at the varying frequency.