Adaptive SRMOS Timing Control for Isolated Power Supply Efficiency
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Solution Overview
Problem
In isolated power supplies operating in discontinuous conduction mode (DCM), the primary side switch mode controller lacks necessary information to turn off the synchronous rectifier metal-oxide-semiconductor (SRMOS) correctly, leading to negative transformer currents and reduced efficiency due to energy flowing from output to input.
Innovation Solution
An adaptive timing control method is implemented, where a controller senses the oscillation waveform after the SRMOS is turned off in a cycle, retrieves a timing point, and adjusts the timing for turning off the SRMOS in the next cycle based on this information to prevent negative transformer currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the primary side switch mode controller uses conventional pulse transformer control for SRMOS, then the control works well in continuous conduction mode (CCM), but it cannot correctly turn off the SRMOS in discontinuous conduction mode (DCM) leading to negative transformer currents
Solution Approach 1:
The patent implements a feedback mechanism where the controller senses the oscillation waveform of the specific voltage (first voltage at the first terminal of the auxiliary winding or second voltage at the first terminal of the auxiliary winding) after the second switch is turned off. The controller retrieves a second timing point based on this oscillation waveform and uses it to adaptively adjust the third timing point for turning off the second switch in the next cycle. This feedback loop enables accurate SRMOS turn-off timing in DCM by continuously monitoring and adjusting based on actual voltage oscillations.
Solution Approach 2:
The patent makes the SRMOS turn-off timing dynamic by adaptively adjusting the third timing point in each cycle based on the oscillation waveform sensed in the previous cycle. Instead of using a fixed timing method that works only for CCM, the system dynamically retunes the turn-off timing according to the actual operating conditions detected through voltage oscillation sensing, enabling reliable operation in both CCM and DCM.
2Loss of energy
If the SRMOS is kept on after transformer energy is completely spent in DCM, then the transformer voltage is clamped by output voltage, but energy flows from output to input creating negative transformer current and reducing efficiency
Solution Approach 1:
The patent applies preliminary action by sensing the oscillation waveform of the specific voltage immediately after the second switch is turned off in each cycle. The controller retrieves the timing information from this oscillation waveform before the next switching cycle begins, and uses this information to proactively adjust the turn-off timing in advance. This preliminary timing adjustment prevents the SRMOS from being turned off too late, thereby preventing negative transformer current before it occurs.
3Adaptability or versatility
If a fixed turn-off timing method is used for SRMOS, then the control is simple, but it cannot adapt to different conduction modes and operating conditions
Solution Approach 1:
The patent implements self-service by having the system automatically sense its own operating state through the oscillation waveform of the specific voltage and autonomously adjust the SRMOS turn-off timing without external intervention. The controller retrieves timing information from the voltage oscillation and automatically retunes the third timing point for the next cycle, enabling the system to self-adapt to different conduction modes (CCM and DCM) and operating conditions.
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 method effectively reduces the occurrence of negative transformer currents, thereby improving the overall efficiency of the isolated power supply by ensuring proper SRMOS turn-off timing in DCM.
Implementation Method 1
The controller senses an oscillation waveform of the specific voltage after the second switch is turned off at a first timing point in a first cycle
Implementation Method 2
pulse transformers are often used to control SRMOS on the secondary side by the primary side switch mode controller
Data Source
AI summary
The present disclosure provides an isolated power supply and a method of controlling the isolated power supply. The isolated power supply includes a primary side circuit and a secondary side circuit. The primary side circuit includes a first switch with a first voltage thereon, an auxiliary winding with a second voltage thereon, and a controller. The secondary side circuit includes a second switch and a pulse transformer. The method includes: retrieving the first voltage or the second voltage as a specific voltage; sensing an oscillation waveform of the specific voltage after the second switch is turned off at a first timing point in a first cycle; retrieving a second timing point based on the oscillation waveform; and controlling the pulse transformer to adaptively adjust a third timing point for turning off the second switch in a second cycle based on the second timing point retrieved in the first cycle.