Synchronous Rectification Control Circuit Timing Adjustment
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Solution Overview
Problem
Synchronous rectification type power circuits in discontinuous conduction mode face inefficiencies due to reverse inductor current flow and voltage ringing issues, which are not adequately addressed by existing control methods.
Innovation Solution
A control circuit adjusts the timing for turning OFF the low-side switch based on a comparison of the output voltage with a reference voltage, using a current direction detecting circuit and a reverse flow detecting circuit to optimize the timing and reduce power loss, by setting a proper detecting operation period to manage ringing and prevent erroneous detections.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the low-side switch is turned OFF to prevent reverse inductor current flow in DCM mode, then power efficiency is improved, but voltage ringing occurs and may exceed power supply voltage
Solution Approach 1:
The control circuit detects the inductor current direction in advance before turning OFF the low-side switch. By using a current direction detecting circuit that monitors the current flow direction through the inductor, the system can determine the optimal timing to turn OFF the low-side switch before reverse current occurs, thereby preventing both efficiency loss and voltage ringing caused by improper timing.
Solution Approach 2:
The system employs a feedback mechanism where the control circuit continuously monitors the inductor current direction and adjusts the low-side switch OFF timing accordingly. The current direction detecting circuit provides real-time feedback about the current flow state, enabling the control circuit to dynamically optimize the switch timing to prevent reverse current while avoiding voltage ringing issues.
2Loss of energy
If the timing for turning OFF the low-side switch is adjusted to the moment inductor current reaches zero, then reverse current flow is prevented, but existing control methods are insufficient to adequately manage voltage ringing
Solution Approach 1:
The patent replaces conventional voltage-based or timing-based control methods with a current direction detection mechanism. Instead of relying on voltage thresholds or fixed timing circuits to determine when to turn OFF the low-side switch, the system uses a current direction detecting circuit that directly senses the inductor current flow direction, providing more accurate and reliable control timing.
Solution Approach 2:
The invention changes the control parameter from voltage-based detection to current direction-based detection. By monitoring the direction of current flow through the inductor rather than relying on voltage levels or timing calculations, the system achieves more precise control over the low-side switch timing, effectively preventing reverse current while managing voltage ringing.
Data Source
AI summary
According to one embodiment, a synchronous rectification type power circuit includes a first power terminal to which a voltage on a high potential side is supplied, a second power terminal to which a voltage on a low potential side is supplied, an output terminal that outputs an output voltage to a load having an inductance and a capacitor, a first switch unit connected between the first power terminal and the output terminal, a second switch unit connected between the second power terminal and the output terminal, a control signal generating circuit which controls ON/OFF of the first and second switch units, and a control circuit that compares the output voltage with a predetermined reference voltage for a predetermined period when the second switch unit is turned OFF. A timing for turning OFF the second switch unit is adjusted based on a result of the comparison.