Valley Mode Switching Fixed Frequency Controller
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Solution Overview
Problem
Switching mode power supplies using valley mode switching face challenges with variable switching frequency due to changes in the switching period, leading to unacceptable frequency variations of up to +/â20%, which can disrupt applications relying on stable power supply frequencies.
Innovation Solution
A controller is configured to select peak current values from a set of calculated values to maintain a fixed frequency, by determining the ringing frequency period and adjusting peak current values accordingly, ensuring that the switching element connects and disconnects the supply at specific voltage valleys, thereby minimizing frequency changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If valley mode switching is used to reduce switching loss, then energy efficiency is improved, but switching frequency becomes variable with unacceptable variations of up to +/â20%
Solution Approach 1:
The patent implements dynamic peak current adjustment by selecting from multiple predetermined peak current values based on operating conditions. The controller dynamically changes the peak current level to compensate for variations in ringing frequency, thereby maintaining a fixed switching frequency while operating in valley mode switching. This dynamic parameter adjustment resolves the contradiction between energy efficiency and frequency stability.
Solution Approach 2:
The patent changes the peak current parameter to maintain fixed switching frequency. By having a set of predetermined peak current values and selecting appropriate values based on operating conditions, the system adjusts this key parameter to compensate for frequency variations. This parameter change strategy allows the system to maintain both valley mode switching benefits and frequency stability.
2Stability of the object's composition
If peak current is increased to maintain fixed frequency, then frequency stability is improved, but stress on switching elements increases
Solution Approach 1:
The system dynamically adjusts peak current based on actual operating conditions and ringing frequency measurements. Rather than using a fixed high peak current, the controller selects from multiple predetermined values, using only as much current as needed to achieve the desired frequency stability. This dynamic approach minimizes unnecessary stress on switching elements while maintaining frequency stability.
Solution Approach 2:
The patent employs multiple predetermined peak current values and selects the appropriate value based on operating conditions. This parameter selection strategy allows the system to use lower peak currents when possible, reducing stress on switching elements, while still achieving frequency stability when needed by selecting higher current values from the predetermined set.
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 allows for quasi-resonance operation at a fixed switching frequency, reduces filter constraints, and maintains a stable power supply frequency, essential for applications sensitive to electromagnetic interference and frequency variations.
Implementation Method 1
drive a switching element to selectively connect a supply to a primary side winding of a transformer to generate a regulated voltage, current, or power at a secondary side winding of the transformer
Implementation Method 2
each peak current value of the plurality of peak current values being calculated to drive an oscillating voltage at the switching element to correspond to a voltage valley at an end of a respective switching cycle
Data Source
AI summary
A controller for a switching mode power converter is configured to drive a switching element to selectively connect a supply to a primary side winding of a transformer to generate a regulated voltage, current, or power at a secondary side winding of the transformer. The controller is configured to, for each switching cycle, select a peak current value from a plurality of peak current values calculated to drive an oscillating voltage at the switching element to correspond to a voltage valley and in response to determining a voltage valley is occurring at the oscillating voltage at the switching element, output an enabling signal to cause the switching element to generate a channel electrically connecting the supply to the primary side winding until current at the switching element is not less than the selected peak current value.