Synchronous Rectification Backflow Detection Circuit
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Solution Overview
Problem
Synchronous rectification DC-DC converters experience backflow issues when the voltage of an external power source, such as a battery, exceeds the output voltage, potentially causing surge voltages that can damage semiconductor elements.
Innovation Solution
A power supply device with a switching element for synchronous rectification, a first current detection circuit, a second current detection circuit with higher response speed, and a control unit that determines backflow by detecting current changes, allowing for timely control of the switching element to mitigate backflow impacts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectification is performed using a FET with backflow prevention circuit, then rectification efficiency is improved, but semiconductor elements may be damaged by surge voltage from backflow when external power source voltage exceeds output voltage
Solution Approach 1:
The control unit determines whether backflow is occurring before the FET enters the on-state by detecting voltage at the switching terminal immediately after turn-off. This preliminary detection allows the system to prevent gate signal output when backflow is detected, avoiding surge voltage damage before it occurs while maintaining synchronous rectification operation under normal conditions
Solution Approach 2:
The backflow prevention circuit continuously monitors the voltage at the switching terminal of the FET after turn-off and feeds this information back to the control unit. Based on this feedback, the control unit dynamically adjusts gate signal output to prevent backflow-induced surge voltages, thereby protecting semiconductor elements while maintaining efficient rectification operation
2Device complexity
If detection timing is delayed, then control simplicity is maintained, but backflow detection accuracy deteriorates causing late response to voltage changes
Solution Approach 1:
The system performs voltage detection at the switching terminal immediately after the FET turn-off moment, which is the earliest possible timing to detect backflow conditions. This preliminary detection approach captures voltage changes at their onset, providing accurate and timely backflow detection information to the control unit before the FET is commanded to turn on again
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
The solution effectively reduces the impact of backflow on components, enabling synchronous rectification across a wider load range and enhancing efficiency, particularly at light loads, and preventing semiconductor element breakdown.
Implementation Method 1
a first secondary winding 33 and a second secondary winding 34, and a third secondary winding 35 of a transformer 30 configured to perform voltage conversion; a switching element 41 or 42 configured to perform synchronous rectification on power to be induced in the first secondary winding 33 or the second secondary winding 34
Implementation Method 2
The synchronous rectification DC-DC converter uses a FET (field effect transistor), and switches between an on-state and an off-state of a gate of the FET at a necessary timing in synchronization with a clock, thus performing operation of the synchronous rectification
Data Source
AI summary
A power supply device includes: a switching element that performs synchronous rectification on a power to be induced in a first secondary wiring of a transformer that performs voltage conversion; a first current detection circuit that detects a value of a current to be induced in a second secondary wiring of the transformer; a second current detection circuit that detects a change in the current to be induced in the second secondary wiring, the second current detection circuit having a higher response speed with respect to conversion of the current than that of the first current detection circuit; and a control unit (control circuit) that determines based on the change in the current detected by the second current detection circuit whether or not backflow is occurring, and controls the switching element in accordance with a result of the determination.