Auxiliary Power Supply for Synchronous Rectification Control
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Solution Overview
Problem
Conventional synchronous rectification switching power supplies face issues with heat generation and potential thermal destruction of the MOSFET due to continuous drain current flow through the body diode when a short-circuit occurs, leading to increased conduction resistance and loss of control over the secondary switching element.
Innovation Solution
Incorporating an auxiliary power supply circuit and a power supply switching circuit that switches the power supply from the DC output voltage to an auxiliary voltage when a voltage decrease is detected, allowing the synchronous rectification control circuit to continue operating and switching the secondary switching element (MOSFET) ON and OFF, preventing continuous drain current flow through the body diode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the synchronous rectification control circuit uses the DC output voltage as power supply, then the circuit operation is simple, but the control circuit cannot operate during output short-circuit conditions
Solution Approach 1:
An auxiliary power supply circuit is introduced as an intermediary power source that activates during output short-circuit conditions. This auxiliary circuit includes a power storage device charged through a current supply circuit, providing backup power to the synchronous rectification control circuit when the main DC output voltage becomes unavailable, thus ensuring continuous operation reliability
2Productivity
If the secondary switching element is not switched OFF during short-circuit, then continuous drain current flows through the body diode, but this causes heat generation and potential thermal destruction
Solution Approach 1:
A voltage decrease detection circuit monitors the DC output voltage and provides feedback to the synchronous rectification control circuit. When a short-circuit condition is detected (voltage decrease), the control circuit receives this feedback signal and responds by switching the secondary switching element OFF, thereby preventing continuous drain current flow through the body diode and eliminating the harmful heat generation effect
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 ensures reliable switching of the MOSFET and prevents heat generation and potential thermal destruction, maintaining efficient operation even during output short-circuits by using an auxiliary supply voltage to maintain control over the MOSFET.
Implementation Method 1
an auxiliary power supply circuit that is configured to be connected to a power storage device and that generates an auxiliary supply voltage by charging the power storage device by the voltage across a source and a drain of the secondary switching element
Implementation Method 2
When the main switching element 4 is then switched OFF, the primary coil 3a of the transformer 3 releases the electrical energy stored therein, thereby inducing an AC voltage in the secondary coil 3b of the transformer 3
Data Source
AI summary
A switching power supply includes an output circuit connected to a secondary coil of a transformer via a secondary switching element and a synchronous rectification control circuit controlling ON/OFF of the secondary switching element based on a detected source-drain voltage of the secondary switching element. The synchronous rectification control circuit includes a voltage detection circuit detecting the source-drain voltage, a switch driving circuit switching the secondary switching element ON/OFF based on the detected source-drain voltage, an auxiliary power supply circuit generating an auxiliary supply voltage from said source-drain voltage, a voltage decrease detection circuit detecting an abnormal voltage drop in a DC output voltage of the output circuit, and a power supply switching circuit switching a power supply for the voltage detection circuit and switch driving circuit from the DC output voltage to the auxiliary supply voltage when the abnormal voltage drop is detected.