Snubber Capacitor Drives Secondary FET Gate in Flyback Converter
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Regulating high-side voltage outputs in switching power converters is challenging due to difficulties in making a field effect transistor (FET) conductive, as it requires sufficient voltage and current to be driven to the gate, which is hard to achieve when the source is at a relatively high voltage.
Innovation Solution
The use of a snubber capacitor on the secondary side of the power converter to store current and drive the gate of the secondary FET during discharge modes, allowing the FET to become conductive before the high-side rectifier is forward-biased, and a secondary-side controller to modulate the on-time based on the high-side voltage output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a FET is used to regulate high voltage output, then voltage regulation capability is improved, but it becomes difficult to make the FET conductive due to insufficient gate voltage and current
Solution Approach 1:
A capacitor is introduced as an intermediary energy storage element between the high voltage source and the FET gate. The capacitor stores energy during the switch off-time and releases it to provide the necessary gate voltage and current during the on-time, enabling the FET to conduct despite the high source voltage
Solution Approach 2:
The capacitor is charged in advance during the FET off-period before the conduction phase begins. This preliminary energy storage ensures that when the FET needs to conduct, the gate already has sufficient voltage and current from the pre-charged capacitor to overcome the high source voltage barrier
2Power
If the FET is made conductive during discharge mode, then high voltage output regulation is achieved, but switching losses increase due to simultaneous current flow
Solution Approach 1:
The circuit operates in periodic cycles, alternating between charging the capacitor during switch off-time and using the stored capacitor energy to drive the FET during on-time. This periodic charge-discharge action separates the energy storage and FET conduction phases, preventing simultaneous current flow and reducing switching losses
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
This approach ensures the secondary FET is conductive prior to current flow, reducing switching losses and effectively regulating the high-side voltage output, even when the source voltage is high.
Implementation Method 1
charging a snubber capacitor coupled to a secondary winding of a transformer arranged for flyback operation; charging a gate of a secondary FET with current from the snubber capacitor
Data Source
AI summary
Driving an electrically controlled switch with a snubber capacitor. At least some example embodiments involve operating a power converter, including: charging a snubber capacitor coupled to a secondary winding of a transformer arranged for flyback operation, the charging during a charge mode of a primary winding the transformer; charging a gate of a secondary field effect transistor (FET) with current from the snubber capacitor, the charging of the gate during a discharge mode of the primary winding, the discharge mode contiguous with the charge mode; providing current through a secondary rectifier and the secondary FET to a secondary output node of the power converter, the secondary rectifier coupled in series with the secondary FET; and making the secondary FET non-conductive.