Short-Circuit Protected Synchronous Rectifier Power Supply Circuit
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Solution Overview
Problem
Switching-mode power supplies with synchronous rectifiers experience excessive power dissipation during output short-circuit, power down, and back bias conditions, leading to undesirable energy loss.
Innovation Solution
Implementing a short-circuit protected power supply circuit that disables the synchronous rectifier and uses diode rectification during load short-circuit or back biased conditions, thereby preventing inductor saturation and reducing component power dissipation. This is achieved through a Schmitt trigger circuit, NOR-logic circuit, or short-circuit sense/protection circuit that controls the synchronous rectifier to switch to or remain in the OFF state when the output node voltage is below a predetermined magnitude.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the synchronous rectifier remains ON during output short-circuit conditions, then rectification continues, but the inductor saturates and component power dissipation increases
Solution Approach 1:
The patent employs feedback control by continuously monitoring the output node voltage and using this information to control the synchronous rectifier's switching state. The Schmitt trigger circuit provides hysteresis-based feedback that reliably detects voltage drops indicating short-circuit conditions, enabling the control circuit to switch off the synchronous rectifier and prevent inductor saturation
Solution Approach 2:
The patent takes preliminary protective action by detecting voltage drops at the output node before severe inductor saturation occurs. The Schmitt trigger and control circuit proactively switch off the synchronous rectifier when adverse conditions are detected, preventing the harmful effect of inductor saturation and excessive power dissipation before they fully develop
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 increases the volt-second product across the inductor during off-time, preventing current run-away and reducing excessive power dissipation, thus enhancing the efficiency of the power supply under adverse conditions.
Implementation Method 1
The Schmitt trigger circuit is coupled to the output node and is configured, upon a voltage magnitude at the output node being less than a predetermined voltage magnitude
Implementation Method 2
The synchronous rectifier is responsive to a synchronous rectifier control signal to selectively switch between an ON state and an OFF state
Implementation Method 3
The output inductor and output capacitor are electrically connected in series with each other to form a series LC circuit
Implementation Method 4
The output inductor and output capacitor are electrically connected in series with each other to form a series LC circuit
Data Source
AI summary
A short-circuit protected power supply circuit includes a switching power supply and a short-circuit sense/protection circuit. The switching power supply includes a synchronous rectifier, an output inductor, and an output capacitor. The synchronous rectifier is responsive to a synchronous rectifier control signal to selectively switch between an ON state and an OFF state. The output inductor and output capacitor are electrically connected in series with each other and are electrically connected in parallel with the synchronous rectifier. An output node is located between the output inductor and output capacitor. The short-circuit sense/protection circuit is coupled to the output node and is configured, upon a voltage magnitude at the output node being less than a predetermined voltage magnitude, to cause the synchronous rectifier control signal to switch the synchronous rectifier to, or keep it in, the OFF state. The short-circuit sense/protection circuit is a Schmitt trigger or an error amplifier/comparator circuit.