Synchronous Rectifier Circuit Using CT Sampling for Precise Switching
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Solution Overview
Problem
Existing synchronous rectifier control circuits are complex and costly due to the need for accurate time sequencing and high-speed voltage sampling, which complicates the control of synchronous rectifier transistors in power supplies, increasing reliability risks and costs.
Innovation Solution
A synchronous rectifier control circuit utilizing a current transformer, bridge rectifier, and comparator, where the current transformer samples secondary-side currents to generate a detection signal, which is processed by the bridge rectifier and comparator to control the synchronous rectifier transistor, enabling high-speed and high-precision control through synchronization with diode conduction and voltage drops.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If control over synchronous rectifier transistor is implemented based on time sequence of primary-side switching transistor using digital signal processor and isolating circuit, then control precision is improved, but device complexity increases and cost increases
Solution Approach 1:
The patent extracts the control function from the complex digital signal processor and isolating circuit system, implementing it directly through the natural characteristics of the bridge rectifier circuit. The control signal is generated by the interaction between the primary-side switching transistor and secondary-side rectifier diode, eliminating the need for separate digital processing and isolation components.
Solution Approach 2:
The bridge rectifier circuit automatically generates the control signal for the synchronous rectifier transistor through its own operating characteristics. The conduction state of the rectifier diode naturally produces the required gate drive signal, making the system self-controlling without external complex control circuits.
2Measurement precision
If control over synchronous rectifier transistor is implemented based on DS end voltage sampling with compensation circuit and high-speed comparator, then control precision is improved, but device complexity increases and cost increases
Solution Approach 1:
The patent removes the compensation circuit and high-speed comparator from the system by utilizing the inherent voltage characteristics of the bridge rectifier. The control signal is derived directly from the rectifier diode's conduction state and the transformer's leakage inductance, eliminating the need for separate voltage sampling and compensation components.
Solution Approach 2:
The patent introduces the leakage inductance of the transformer and the body diode of the rectifier as intermediary elements that naturally generate the control signal. These elements mediate between the primary-side switching and secondary-side rectification, producing the required gate drive signal through their physical characteristics rather than active electronic components.
3Measurement precision
If complex control circuits with digital signal processor or compensation circuit are used, then control precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent replaces expensive digital signal processors, isolating circuits, and high-speed comparators with inexpensive passive components such as the bridge rectifier diode and transformer leakage inductance. These components are standard elements already present in the power converter, eliminating the need for additional costly parts.
Solution Approach 2:
The bridge rectifier diode serves multiple functions: it performs rectification and simultaneously generates the control signal for the synchronous rectifier transistor. The transformer leakage inductance also serves dual purposes in the control mechanism. This multi-functionality reduces the total component count and manufacturing cost.
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 simplifies and cost-reduces the control of synchronous rectifier transistors, achieving high-speed and high-precision control while maintaining reliability, as long as a faint current exists, thereby improving power supply efficiency and reducing heat loss.
Implementation Method 1
a current transformer CT, a bridge rectifier and a comparator, wherein the current transformer CT is connected in series to a secondary side, performs sampling on a loop current of the secondary side to obtain a current detection signal
Implementation Method 2
the bridge rectifier acquires a secondary-side sampling current according to the current detection signal, and outputs the secondary-side sampling current to the comparator, so that the comparator generates a voltage difference, and an output signal of the comparator is inverted
Data Source
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AI summary
Embodiments of the present invention disclose a synchronous rectifier control circuit and method. In the embodiments of the present invention, the synchronous rectifier control circuit includes a current transformer CT, a bridge rectifier, and a comparator, where the current transformer CT is connected in series to a secondary side, performs sampling on a loop current of the secondary side to obtain a current detection signal, and outputs the obtained current detection signal to the bridge rectifier; the bridge rectifier acquires a secondary-side sampling current according to the current detection signal, and outputs the secondary-side sampling current to the comparator, so that the comparator generates a voltage difference; and an output signal of the comparator turns over, so as to control on and off of a synchronous rectifier transistor. In this way, high-speed and high-precision control over a synchronous rectifier transistor can be implemented. The control is simple and is low in cost.