Quasi Resonant Mode Controller Jitter for EMI Reduction
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Solution Overview
Problem
Quasi resonant mode switching power supplies fail to effectively reduce electromagnetic interference due to fixed switching frequencies, leading to unsatisfactory compliance with electromagnetic interference specifications.
Innovation Solution
A controller and method that utilize a feedback pin, voltage generation unit, pulse generator, and comparator to generate a switching signal with a variable reference voltage, allowing the switching frequency of the power switch to vary, thereby reducing peak electromagnetic interference through power dispersion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the power switch operates at a fixed frequency, then the switching power supply can maintain stable power conversion, but it radiates electromagnetic waves at a specific frequency causing electromagnetic interference
Solution Approach 1:
The patent applies dynamics by transitioning from fixed-frequency switching to variable-frequency switching. The controller dynamically adjusts the switching frequency of the power switch based on feedback signals, allowing the system to adapt its operating frequency rather than remaining static. This dynamic adjustment prevents consistent radiation at a single frequency while maintaining stable power conversion through closed-loop control.
Solution Approach 2:
The patent implements parameter changes by modifying the switching frequency parameter. The controller varies the switching frequency within a predetermined range according to feedback voltage, thereby changing the operational parameters of the power switch. This parameter variation disperses the electromagnetic energy across multiple frequencies, reducing peak interference while preserving power conversion stability.
2Object-generated harmful factors
If the switching frequency is varied to reduce electromagnetic interference, then power dispersion is achieved, but the complexity of the control system increases
Solution Approach 1:
The patent employs feedback mechanisms where the controller receives feedback voltage from the power converter and uses this information to adjust the switching frequency. This feedback loop enables automatic frequency modulation without requiring complex external control circuits. The feedback signal provides real-time information about the system state, allowing the controller to optimize the switching frequency dynamically while keeping the control architecture relatively simple.
Solution Approach 2:
The controller is designed to perform multiple functions: it manages power conversion, generates switching signals, processes feedback voltage, and modulates switching frequency all within a single integrated device. This multi-functionality reduces the need for separate dedicated circuits for each function, thereby limiting the increase in overall system complexity while achieving the desired frequency variation for electromagnetic interference reduction.
3Object-generated harmful factors
If a variable reference voltage is used to generate jittered switching signals, then electromagnetic interference is reduced through power dispersion, but the precision of voltage control may be affected
Solution Approach 1:
The patent applies partial action by varying the reference voltage only within a predetermined range rather than allowing unlimited variation. This limited range adjustment is sufficient to achieve power dispersion and reduce electromagnetic interference while minimizing the impact on voltage control precision. The variation is controlled to be just enough to scatter electromagnetic energy without compromising the overall voltage regulation accuracy.
Solution Approach 2:
The patent maintains continuous useful action by ensuring that the variable reference voltage continuously adjusts the switching frequency in response to feedback signals. This continuous adjustment process ensures that power dispersion is consistently achieved to reduce electromagnetic interference, while the ongoing feedback control compensates for any precision variations, maintaining overall voltage control accuracy throughout operation.
Data Source
AI summary
A controller for generating jitters in a quasi resonant mode includes a feedback pin, a voltage generation unit, a pulse generator, and a comparator. The feedback pin is used for receiving a feedback voltage from a secondary side of a power converter. The voltage generation unit is used for generating a first voltage according to the feedback voltage and a pulse. The pulse generator is used for generating the pulse when a control signal controlling a power switch of a primary side of the power converter is enabled. The comparator is used for controlling enabling and disabling of a switching signal according to the first voltage and a variable reference voltage. The variable reference voltage is monotonously swung within a predetermined range according to a digital signal.