Switching Mode Power Supply Block Time Control
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Solution Overview
Problem
Switching mode power supplies, particularly quasi-resonance converters, face challenges with electromagnetic interference (EMI) and audible noise due to unstable valley switching, which are not effectively addressed by existing solutions.
Innovation Solution
The introduction of a load representative signal that controls the block time, allowing jittering of the block time to vary the switching frequency, and the implementation of a QR controller with a valley detector, discharge time detector, and jittering apparatus to stabilize valley switching, thereby reducing EMI and noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If valley switching is used to minimize switching loss, then power conversion efficiency is improved, but instability in valley switching causes EMI and audible noise
Solution Approach 1:
The patent applies dynamics by making the block time variable rather than fixed. The jittering apparatus dynamically adjusts the block time based on a load representative signal, causing the switching frequency to vary over time. This dynamic adjustment stabilizes valley switching by preventing the system from settling into a fixed pattern that causes instability, thereby reducing EMI and audible noise while maintaining efficient power conversion.
Solution Approach 2:
The patent changes the parameter of block time from a constant value to a variable value that responds to load conditions. By using the jittering apparatus to modulate the block time according to the load representative signal, the switching frequency becomes adaptive. This parameter change allows the system to maintain optimal switching behavior across different operating conditions, eliminating the instability associated with fixed block times.
2Device complexity
If block time is fixed to define maximum switching frequency, then switching frequency control is simplified, but instability in valley switching occurs causing EMI and noise
Solution Approach 1:
The patent transforms the static block time into a dynamic parameter that automatically adjusts with load conditions. The jittering apparatus introduces controlled variations in block time based on the load representative signal, creating a dynamic control mechanism. This dynamic approach maintains simplicity in the overall control structure while effectively preventing the instability that arises from fixed block times, thereby reducing EMI and audible noise.
3Productivity
If compensation signal controls both ON time and block time, then power conversion regulation is achieved, but instability in valley switching persists causing audible noise
Solution Approach 1:
The patent segments the control functions by separating the control of ON time and block time. The compensation signal continues to control the ON time for power regulation, while the jittering apparatus independently controls the block time based on the load representative signal. This segmentation allows each control parameter to be optimized for its specific function, maintaining power conversion efficiency while eliminating the instability that causes audible noise.
Solution Approach 2:
The patent applies dynamics to the block time control by introducing the jittering apparatus that modulates block time according to load conditions. This dynamic adjustment of block time, independent of the compensation signal control, stabilizes valley switching by preventing fixed-pattern instability. The result is reduced audible noise while maintaining the power conversion regulation achieved through compensation signal control.
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
This approach effectively eliminates instability in valley switching, reducing EMI and audible noise, ensuring a stable and efficient power conversion process.
Implementation Method 1
a transformer, an inductive device, has a primary winding PRM, a secondary winding SEC and an auxiliary winding AUX, all inductively coupled to each other
Data Source
AI summary
A power controller provides a block time in response to an output current to an output load, and the block time determines a maximum switching frequency of a switching mode power supply. An exemplifying power controller has an output current estimator, a block time generator, and a pulse width modulator. The output current estimator provides a load representative signal in response to a discharge time of the inductive device and a current sense signal, wherein the current sense signal represents a current through an inductive device. The block time generator provides a block time based on the load representative signal. The pulse width modulator generates a pulse-width-modulation signal to control a power switch in response to a compensation signal, which is in response to the output voltage to the output load. The cycle time of the pulse-width-modulation signal is limited to be not less than the block time.