LLC Converter Synchronous Rectifier Delay for Shoot-Through Prevention
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Solution Overview
Problem
In LLC converters, secondary side conduction does not always coincide with primary side conduction, leading to shoot-through conditions during heavy continuous conduction mode, affecting converter performance, life, and efficiency.
Innovation Solution
A circuit and method that measure the synchronous rectifier delay based on input voltage and apply a delay between the transition of primary and secondary side switches to prevent simultaneous conduction, using a controller to manage the gate voltages and ensure proper timing of switch transitions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If secondary side switches are turned on at the same time with corresponding primary side switches, then switching losses are reduced, but shoot-through conditions occur during heavy continuous conduction mode affecting converter performance and efficiency
Solution Approach 1:
The patent applies preliminary action by measuring the input voltage and calculating the required synchronous rectifier delay before actuating the secondary side switches. The controller determines the appropriate delay time based on the measured voltage conditions, ensuring that the secondary side switches are turned on at the optimal moment rather than simultaneously with primary side switches. This prevents shoot-through conditions while minimizing switching losses.
2Reliability
If synchronous rectifier delay is applied to prevent shoot-through conditions, then converter reliability is improved, but switching timing precision requirements increase
Solution Approach 1:
The patent employs parameter changes by dynamically adjusting the synchronous rectifier delay based on the measured input voltage. The controller modifies the delay parameter according to voltage conditions, allowing the system to adapt to different operating scenarios. This approach simplifies the timing control requirements compared to fixed precision timing, as the delay is calculated and adjusted based on measurable voltage parameters rather than requiring absolute timing precision.
Data Source
AI summary
A circuit for use in an LLC converter comprises a first primary side switch, a first secondary side switch assembly, and a controller. The controller is configured to measure, on the primary side of the LLC converter, a first voltage and determine, based on the first voltage, a delay due to the first voltage. The controller is also configured to apply a first gate voltage to the first primary side switch to transition the first primary side switch from an off state to an on state and apply a second gate voltage to the first secondary side switch assembly to transition the first secondary side switch assembly from an off state to an on state. The application of the first gate voltage and the application of the second gate voltage are separated by a synchronous rectifier delay based at least on the delay due to the first voltage.