Bootstrap Recharge System for Dual-Switch Flyback Converters
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Solution Overview
Problem
In dual-switch flyback converters, the bootstrap capacitor fails to recharge adequately due to insufficient energy from the leakage inductance, leading to an inability to activate the high-side switch, which disrupts the converter's operation.
Innovation Solution
A bootstrap recharge system is introduced, which includes a controller that provides control signals to activate an auxiliary switch in conjunction with the high-side and low-side switches. The auxiliary switch is activated based on conditions related to the voltage across the bootstrap capacitor and the floating ground node, ensuring adequate recharging of the bootstrap capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the converter relies on leakage inductance energy to recharge the bootstrap capacitor, then the structure remains simple, but the bootstrap capacitor fails to recharge adequately when leakage inductance energy is insufficient
Solution Approach 1:
An auxiliary switch is introduced as an intermediary component to facilitate the recharging of the bootstrap capacitor. The auxiliary switch creates an additional current path that allows the bootstrap capacitor to recharge reliably even when leakage inductance energy is insufficient, without significantly complicating the overall converter structure
Solution Approach 2:
The auxiliary switch is activated in advance during the off-state of the main switch to prepare the current path for bootstrap capacitor recharging. This preliminary action ensures that the bootstrap capacitor is recharged before the next switching cycle begins, preventing operation failure
2Reliability
If the combined value of reflected voltage and voltage spike from leakage inductance is less than input voltage, then the converter operates with limited energy, but the floating ground node potential does not reach zero preventing bootstrap capacitor recharging
Solution Approach 1:
The auxiliary switch serves as a mediator that enables the floating ground node to reach zero potential through an alternative path. By controlling the auxiliary switch, the system ensures the bootstrap capacitor can recharge even when the natural voltage spike from leakage inductance is insufficient
Solution Approach 2:
The auxiliary switch is controlled based on the actual operating conditions of the converter, allowing the system to self-adjust and ensure proper bootstrap capacitor recharging without external intervention. The controller monitors the voltage conditions and activates the auxiliary switch only when needed
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 proposed solution ensures reliable recharging of the bootstrap capacitor, maintaining the converter's operation by ensuring the high-side switch can be activated, thus addressing the issue of inadequate recharging due to insufficient leakage inductance energy.
Implementation Method 1
The auxiliary switch has a drain terminal coupled to the bootstrap capacitor through the floating ground node
Implementation Method 2
The presence of substantial energy from the leakage inductance of the transformer can draw the potential at the floating ground (FGND) close to zero
Implementation Method 3
The bootstrap capacitor has a first terminal coupled to a floating ground node
Data Source
AI summary
According to an embodiment, a converter includes a bootstrap capacitor, a high-side switch, a low-side switch, an auxiliary switch, and a controller. The bootstrap capacitor has a first terminal coupled to a floating ground node. The high-side switch has a source terminal coupled to the bootstrap capacitor through the floating ground node. The auxiliary switch has a drain terminal coupled to the bootstrap capacitor through the floating ground node. The controller provides a first control signal to a control terminal of the high-side switch, provides a second control signal to a control terminal of the low-side switch, and provides a third control signal to a control terminal of the auxiliary switch. The third control signal is based on a condition associated with the converter after the first control signal and the second control signal deactivate the high-side switch and the low-side switch respectively.