SMPS Secondary Switch Control for Dynamic Load Response
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Solution Overview
Problem
Conventional switching mode power supplies with primary side regulation suffer from unqualified dynamic load response, particularly at lower switching frequencies, due to the inability to detect output voltage and load conditions during the discontinuous conduction time period, leading to significant output voltage undershoot and reduced efficiency.
Innovation Solution
The implementation of a switching mode power supply with a transformer, primary and secondary windings, and an auxiliary winding, along with a feedback circuit and controllers that utilize a secondary controller with hysteresis comparison and timing circuits to detect load changes and control the primary switch based on secondary switch conduction, enabling timely response to load increases and reducing output voltage undershoot.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If conventional primary side regulation is used, then the power supply structure is simple, but the dynamic load response is unqualified and output voltage undershoot occurs
Solution Approach 1:
The patent segments the rectifying function into two parts: a secondary rectifying diode for normal operation and a secondary switch for active load regulation. This segmentation allows the secondary switch to actively respond to load changes during the discontinuous conduction period, improving dynamic load response while maintaining the overall simplicity of the primary side regulation structure.
Solution Approach 2:
The patent implements feedback by having the primary controller detect the conduction state of the secondary switch and adjust the primary switch accordingly. This feedback mechanism enables the system to respond to load changes in real-time, preventing output voltage undershoot while maintaining structural simplicity.
2Loss of energy
If the switching frequency is reduced, then the power loss is reduced, but the dynamic load response becomes slower due to longer discontinuous conduction period
Solution Approach 1:
The patent ensures continuous useful action by having the secondary switch actively regulate the output during the discontinuous conduction period. This continuous regulation capability allows the system to maintain fast dynamic load response even at lower switching frequencies, as the secondary switch can immediately respond to load changes without waiting for the next switching cycle.
Solution Approach 2:
The secondary switch operates autonomously during the discontinuous conduction period, self-regulating the output voltage in response to load changes. This self-service capability eliminates the need for high switching frequency to maintain fast response, as the secondary switch independently handles load regulation.
3Productivity
If the discontinuous conduction period is extended, then the power supply operates efficiently at light load, but the output voltage undershoot increases when load increases
Solution Approach 1:
The patent applies preliminary anti-action by having the secondary switch preemptively respond to load increases during the discontinuous conduction period. When the load increases, the secondary switch activates to prevent output voltage undershoot before it can significantly affect the system, thereby eliminating the harmful effect while maintaining efficient light-load operation.
Solution Approach 2:
The secondary switch is positioned to act in advance during the discontinuous conduction period, preparing to regulate the output voltage before load changes can cause significant undershoot. This preliminary action capability allows the system to maintain both high efficiency at light load and fast response to load increases.
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 solution significantly reduces output voltage undershoot and improves dynamic load response by allowing for immediate detection and adjustment during discontinuous conduction periods, enhancing the overall performance of switching mode power supplies.
Implementation Method 1
a hysteresis comparison circuit configured to compare the voltage across the secondary switch with a first secondary threshold and a second secondary threshold and configured to generate a hysteresis comparison signal
Implementation Method 2
a transformer having a primary winding, a secondary winding for providing an output voltage
Data Source
AI summary
A switching mode power supply (SMPS) includes a transformer having a primary winding, a secondary winding for providing an output voltage and an auxiliary winding, a primary switch coupled to the primary winding, a secondary rectifying diode coupled to the secondary winding and a secondary switch connected in parallel with the secondary rectifying diode. A control method used in the SMPS includes: comparing a voltage across the secondary switch with a first secondary threshold and a second secondary threshold and generating a hysteresis comparison signal; timing based on the hysteresis comparison signal; comparing the voltage across the secondary switch with a third secondary threshold when the timing period reaches a first predetermined time; turning ON the secondary switch when the voltage across the secondary switch is less than a third secondary threshold; and turning on the primary switch when the conduction of the secondary switch is detected.