Synchronous Rectifier Start-Up Control Against Parasitic Turn-On
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Solution Overview
Problem
Conventional synchronous rectification controllers fail to prevent rectification switches from being mistakenly turned on due to parasitic capacitance during the start-up stage of a power converter when the controller is not yet fully operational.
Innovation Solution
A synchronous rectification controller with a transistor and start-up control module that limits the cross voltage between the rectification switch terminals to be below a threshold voltage during the start-up stage, using a transistor to keep the switch off until the operating voltage exceeds a threshold, and then allowing normal operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the synchronous rectification controller is not yet fully operational during start-up stage, then the controller cannot properly control the rectification switch, but the parasitic capacitance causes the rectification switch to be mistakenly turned on
Solution Approach 1:
The patent applies preliminary anti-action by introducing a start-up control module that actively counteracts the parasitic capacitance effect before the synchronous rectification controller is fully operational. The module detects the start-up stage and generates a start-up control signal to keep the rectification switch in an off state, preventing the harmful effect of parasitic capacitance from causing mistaken turn-on before the controller is ready.
Solution Approach 2:
The patent uses an intermediary approach by introducing a start-up control module as a mediator between the power receiving terminal and the rectification switch control terminal. This module includes a transistor that acts as a switch to control the connection between these terminals, allowing indirect control of the rectification switch during the critical start-up period when the main controller is not yet operational.
2Reliability
If conventional dead time adjustment or current source charging methods are used, then the rectification switch can be locked during normal operation, but these methods require the synchronous rectification controller to be already in operation
Solution Approach 1:
The patent applies preliminary action by enabling the rectification switch locking capability before the synchronous rectification controller is fully operational. The start-up control module is designed to be activated during the start-up stage and generates the necessary control signals to keep the rectification switch in an off state, establishing the locking capability in advance of when the main controller becomes operational.
3Reliability
If the cross voltage between gate and source of the rectification switch is allowed to rise due to parasitic capacitance, then the switch may turn on mistakenly, but completely suppressing the voltage rise may affect normal switching operation
Solution Approach 1:
The patent applies dynamics by making the control approach adaptive to different operational stages. The start-up control module dynamically adjusts its control action based on the operational state: during start-up stage, it suppresses the cross voltage to prevent mistaken turn-on; once the synchronous rectification controller is fully operational, the module stops its suppression action, allowing normal switching operation to proceed without interference.
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
Prevents the rectification switch from being mistakenly turned on by parasitic capacitance, ensuring reliable start-up and operation of the power converter.
Implementation Method 1
there is a parasitic capacitance Cgd between a drain D and a gate G of the rectification switch SR. Therefore, when part of the energy of the primary-side circuit 100-1 is coupled to the secondary-side circuit 100-2 through the transformer 100-3, the parasitic capacitance Cgd may be charged so as to cause the voltage at a rectification switch control terminal G to rise
Data Source
AI summary
A synchronous rectification controller is coupled to a rectification switch at a secondary-side of a power converter, and the rectification switch includes a rectification switch control, first, and second terminal. The synchronous rectification controller includes a driving signal terminal, a power receiving terminal, a transistor, and a start-up control module. The power receiving terminal receives an operating voltage, and when the operating voltage is higher than an operating voltage threshold, the synchronous rectification controller can output a driving signal for driving the rectification switch through the driving signal terminal. When the operating voltage is lower than the operating voltage threshold, the start-up control module limits a cross voltage between the rectification switch control terminal and the rectification switch second terminal to be lower than a first threshold voltage of the rectification switch by turning on the transistor to prevent conduction of the rectification switch.