Synchronous Rectifier Driving via Drain-Source Voltage Detection
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Solution Overview
Problem
Conventional synchronous rectifier driving methods face challenges in obtaining isolated driving signals effectively, leading to increased costs and size due to parasitic inductance in current transformers and difficulties in acquiring control signals during discontinuous current modes, which result in reverse current issues.
Innovation Solution
The apparatus includes detection circuits to detect drain and source voltages of synchronous rectifiers, generating isolated driving signals through an isolated driving circuit using push-pull circuits and an isolated driving transformer, ensuring accurate current direction indication and isolation for synchronous rectification.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a current transformer is used to detect current for synchronous rectifier control, then current detection is achieved, but parasitic inductance causes signal delay and interference, increasing cost and size
Solution Approach 1:
The patent extracts the detection function from the traditional current transformer approach and implements it through voltage detection across the synchronous rectifier tube. By detecting the voltage between source and drain terminals, the system obtains current direction information without using a current transformer, thereby eliminating parasitic inductance issues and reducing circuit complexity
Solution Approach 2:
The patent introduces an intermediary approach by using voltage detection as a mediator to infer current direction. Instead of directly measuring current with a transformer, the system measures voltage across the rectifier tube and uses this intermediate measurement to determine current flow direction, avoiding the problems associated with current transformers
2Ease of manufacture
If control signal is taken from main power mosfet, then driving signal is easy to obtain, but reverse current flows in discontinuous current mode, affecting circuit operation
Solution Approach 1:
The patent implements feedback by continuously monitoring the voltage between source and drain terminals of the synchronous rectifier tube. This feedback mechanism allows the system to detect current direction in real-time and adjust the driving signal accordingly, preventing reverse current flow in discontinuous current mode while maintaining reliable circuit operation
Solution Approach 2:
The synchronous rectifier tube performs self-service by using its own voltage characteristics to generate control information. The voltage across the tube during conduction provides natural feedback about current direction, allowing the tube to essentially control itself without relying on external main power mosfet signals that may not account for discontinuous current mode 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 approach allows for simple and effective generation of isolated driving signals, providing superior protection against shoot-through and other abnormalities, improving the overall performance of synchronous rectifier circuits.
Implementation Method 1
an isolated driving transformer, wherein an input end of each of the two push-pull circuits may be connected to one of the detection circuits; and a primary winding of the isolated driving transformer may be connected to output ends of the two push-pull circuits, and each of two secondary windings of the isolated driving transformer may be connected to a gate and source of one of synchronous rectifiers
Data Source
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AI summary
Provided is apparatus and a method for driving synchronous rectifiers, which relate to the field of power supplies for communications. The apparatus includes: detection circuits, wherein each of the detection circuits is configured to detect drain and source voltages of one of synchronous rectifiers to obtain a detection signal for indicating a current direction in the one of the synchronous rectifiers; an isolated driving circuit, configured to generate isolated driving signals for driving the synchronous rectifiers according to the detection signals output by the detection circuits; and the synchronous rectifiers, configured to synchronously rectify input signals from a main transformer by using the isolated driving signals. The present disclosure can obtain the isolated driving signals of the synchronous rectifiers simply and effectively, and has a superior protective feature in case of shoot-through and other abnormalities.