Synchronous Rectifier Power Supply Protection Against Body Diode Loss
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Solution Overview
Problem
Conventional power supply devices using synchronous rectifier elements face issues with increased loss and potential damage due to the body diode conduction when control signals fail to be supplied to MOS transistors, leading to insufficient heat dissipation.
Innovation Solution
Incorporation of an abnormality detection circuit to detect failures in the synchronous rectifier element drive circuit, coupled with a load current detection circuit and protection circuit to prevent damage by adjusting operating conditions and limiting current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a synchronous rectifier element (MOS transistor) is used instead of a diode, then the loss is reduced and efficiency is improved, but the risk of body diode conduction increases when control signals fail, leading to increased loss and potential damage
Solution Approach 1:
The abnormality detection circuit proactively monitors the drive circuit status before failure leads to body diode conduction. By detecting abnormalities in advance (such as drive signal waveform anomalies or timing issues), the system can take preventive action to avoid the harmful state, thus maintaining reliability while preserving the low-loss benefit of synchronous rectification
Solution Approach 2:
The protection circuit implements a feedback mechanism where the abnormality detection circuit continuously monitors the drive circuit and provides feedback signals. When an abnormality is detected, the feedback triggers the protection circuit to limit current or shut down, preventing body diode conduction and its associated losses and damage, thereby resolving the reliability concern while maintaining efficient operation under normal conditions
2Device complexity
If the synchronous rectifier element is operated without abnormality detection and protection circuits, then the device complexity is reduced, but the risk of damage due to body diode conduction increases
Solution Approach 1:
The abnormality detection circuit acts as an intermediary between the drive circuit and the synchronous rectifier element. It monitors the drive circuit's output without directly interfering with the main power path, and only activates the protection circuit when abnormalities are detected. This intermediary approach provides protection against body diode conduction while adding minimal complexity to the overall system
Solution Approach 2:
The protection circuit is designed to activate only when abnormalities are detected by the detection circuit, rather than being continuously active. This preliminary detection approach allows the system to operate simply under normal conditions while providing protection only when needed, thus balancing complexity reduction with harm prevention
Data Source
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AI summary
A power supply device (1) includes an intermittent voltage generation circuit (110), a rectifying and smoothing circuit (120), a synchronous rectifier element drive circuit (17), an abnormality detection circuit (130), a load current detection circuit (150), and a protection circuit (160). The intermittent voltage generation circuit (110) generates an intermittent voltage from an input voltage from an external power supply by a switching element that is repeatedly turned on and off. The rectifying and smoothing circuit (120) rectifies the intermittent voltage by a synchronous rectifier element that is turned on and off in synchronization with on and off of the switching element, smooths the intermittent voltage by a capacitor, and supplies the intermittent voltage to a load. The synchronous rectifier element drive circuit (17) supplies a control signal for turning on and off the synchronous rectifier element to a control terminal of the synchronous rectifier element. The abnormality detection circuit (130) detects an abnormality in the synchronous rectifier element drive circuit. The load current detection circuit (150) detects a load current that is a current of the load supplied by the rectifying and smoothing circuit. The protection circuit (160) performs a protection operation on the basis of a detection result of the abnormality detection circuit and a detection result of the load current detection circuit.