Isolated Voltage Converter Snubber Feedback Control
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Solution Overview
Problem
The existing isolated voltage converters with feedback on the primary winding face challenges in maintaining efficient regulation and stability, particularly in burst-mode conditions, due to the presence of a passive snubber network which can affect the reading of the output voltage and lead to energy peaks, causing instability and electromagnetic interference.
Innovation Solution
The implementation of a burst-mode control stage that enables sampling of the feedback voltage only when the clamp capacitor of the snubber network is adequately charged, and pre-charging the capacitor before sampling to ensure accurate feedback, thereby preventing energy peaks and maintaining efficient regulation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a passive snubber network is used in the voltage converter, then voltage spikes and electromagnetic interference are reduced, but the clamp capacitor charging process causes energy peaks and instability in burst-mode conditions
Solution Approach 1:
The control circuit performs preliminary action by detecting the voltage across the clamp capacitor before sampling the feedback voltage. When the clamp capacitor voltage reaches a predetermined threshold, the control circuit enables feedback sampling. This preliminary detection and conditional enabling prevents energy peaks by ensuring the snubber network is fully charged before feedback is taken, thereby maintaining regulation stability while still benefiting from the electromagnetic interference reduction of the passive snubber network
2Measurement precision
If feedback voltage is sampled at the end of demagnetization, then the feedback voltage accurately reflects the output voltage, but the presence of the snubber network can distort this reading
Solution Approach 1:
The control circuit implements a conditional feedback mechanism where it continuously monitors the clamp capacitor voltage and only enables feedback sampling when the clamp capacitor is adequately charged. This feedback control ensures that the feedback voltage sampled from the auxiliary winding accurately reflects the output voltage by eliminating the distortion caused by an uncharged or partially charged snubber network, thus maintaining both measurement precision and information integrity
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 stable and efficient regulation of the output voltage, preventing energy peaks and associated issues like electromagnetic interference, while maintaining the efficiency of the voltage converter, even in low-load conditions.
Implementation Method 1
a transformer having a primary winding receiving the input voltage, and a secondary winding supplying the regulated output voltage
Implementation Method 2
a passive snubber network comprising a clamp capacitor coupled across the primary winding of the transformer
Data Source
AI summary
An embodiment of a voltage converter, provided with: a voltage transformer having a primary winding receiving an input voltage, a secondary winding supplying an output voltage, and an auxiliary winding supplying a feedback voltage correlated to the output voltage; a main switch, coupled to the primary winding; a control circuit, which controls switching of the main switch and has a sampling stage for sampling and holding the feedback voltage and supplying a sampled signal; and a voltage limiting circuit, provided with a clamp capacitor, designed to be coupled across the primary winding. A sampling control stage is coupled to the sampling stage, and is designed, during a given operating condition of the voltage converter, to enable updating of the sampled signal on the basis of a state of charge of the clamp capacitor.