Adaptive Turn-On Delay for LLC Converter Inversion Currents
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Solution Overview
Problem
In LLC converters, low load conditions lead to capacitive current spikes during switching device turn-off, causing mis-triggering and efficiency loss due to inversion currents discharging the output capacitor.
Innovation Solution
Implementing an adaptive turn-on delay mechanism in the SR controller, which adjusts the gate control signal based on load detection, increasing the turn-on delay during low load conditions to prevent inversion currents by using a gate signal control circuit and SR driver that adjusts the turn-on delay in response to a load detection signal, thereby maintaining an optimal dead time interval.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the switching devices are turned off in low load condition, then the capacitive current spike is generated, but this causes mis-triggering and inversion current through the switching device
Solution Approach 1:
The gate signal control circuit introduces a turn-on delay to the driver input signal before generating the gate control signal. This preliminary action prevents the capacitive current spike from causing mis-triggering by ensuring the switching device is fully turned off before the next turn-on command is issued, especially in low load conditions where the spike phenomenon occurs
Solution Approach 2:
The system dynamically adjusts the turn-on delay based on load detection. The SR driver increases the turn-on delay when low load condition is detected (via the load detection signal), and uses a shorter delay under normal load conditions. This dynamic adjustment prevents inversion currents while maintaining efficient operation across different load scenarios
2Reliability
If the turn-on delay is increased to prevent mis-triggering, then inversion current is prevented, but the dead time interval becomes longer affecting switching efficiency
Solution Approach 1:
The turn-on delay is dynamically adjusted based on load detection. Under low load conditions where inversion current risk exists, a longer turn-on delay is applied to ensure reliable prevention. Under normal load conditions, a shorter delay is used to minimize dead time and maintain switching efficiency. This dynamic adaptation resolves the contradiction by applying the appropriate delay only when necessary
3Device complexity
If a fixed turn-on delay is used, then the circuit operation is simple, but it cannot prevent inversion current in varying load conditions
Solution Approach 1:
The system implements feedback through load detection. The load detection signal is generated based on the actual load condition, and this feedback signal controls the SR driver to adjust the turn-on delay accordingly. This feedback mechanism ensures inversion current prevention under low load conditions while maintaining simple operation under normal conditions
Solution Approach 2:
The gate signal control circuit automatically adjusts its own turn-on delay based on load detection without external intervention. The system self-regulates by using the load detection signal to control the SR driver's delay adjustment, eliminating the need for complex external control circuits
Data Source
AI summary
A method for controlling a power converter includes generating a load detection signal in response to a conduction signal and a driver input signal, and generating a gate control signal in response to the load detection signal. The gate control signal is delayed by a delay amount in response to the load detection signal. An apparatus for controlling a power converter includes a gate signal control circuit generating a load detection signal in response to a conduction signal and a driver input signal, and a synchronous rectifier (SR) driver generating a gate control signal in response to the load detection signal.