Rectifier Control Device for LLC Converter Gate Discharge
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Solution Overview
Problem
In LLC resonant converters, secondary rectification losses limit efficiency, and existing synchronous rectification techniques are hindered by parasitic inductances causing premature turn-off of transistors and noise issues due to discharge paths.
Innovation Solution
A control device for rectifiers in switching converters that employs a slow and fast discharge path mechanism for transistor control terminals, using a combination of PMOS and NMOS transistors to manage parasitic inductances and reduce noise on internal ground and supply voltage nodes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If synchronous rectification technique is used to replace rectifier diodes with power MOSFETs, then voltage drop and power dissipation are reduced, but parasitic inductances cause premature turn-off of transistors and noise issues arise due to discharge paths
Solution Approach 1:
The discharge path for the transistor gate is segmented into two separate paths: a fast discharge path using an NMOS transistor for rapid gate voltage reduction, and a slow discharge path using a PMOS transistor for controlled, noise-free discharge. This segmentation allows each path to optimize for its specific function, resolving the contradiction between fast turn-off and noise reduction.
Solution Approach 2:
The control device acts as an intermediary between the synchronous rectifier transistors and the discharge paths, intelligently selecting which discharge path to activate based on operational conditions. This intermediary function coordinates the switching actions to achieve both fast response when needed and noise-free operation during normal conditions.
2Speed
If fast discharge path is used to quickly discharge transistor gate, then turn-off speed is improved, but noise on internal ground and supply voltage nodes increases
Solution Approach 1:
The discharge functionality is divided into two distinct circuits: a fast discharge circuit using an NMOS transistor that provides rapid gate voltage reduction when needed, and a slow discharge circuit using a PMOS transistor that provides controlled, noise-free discharge during normal operation. This segmentation allows the system to have both fast turn-off capability and low-noise operation without compromise.
Solution Approach 2:
The discharge path characteristics are made dynamic by using different transistor types with different discharge rates. The system can switch between a fast discharge mode (NMOS) and a slow discharge mode (PMOS) depending on operational requirements, allowing optimization of both speed and noise performance in different operating conditions.
Data Source
AI summary
A control device controls a rectifier of a switching converter that is supplied with an input voltage and provides an output current. The rectifier is configured to rectify the output current of the converter and has at least one transistor. The control device, when the at least one transistor is turned off, provides a slow discharge path to ground in a normal operation condition and provides a fast discharge path to ground for discharging the control terminal of the at least one transistor in response to detecting a zero cross event of the current flowing through said at least one transistor.