Half-Bridge Low-Side Split Transistor Timing for Reverse Recovery Elimination
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The reverse recovery charge of the low-side transistor in switching power conversion circuits is a significant efficiency killer, particularly exacerbated by increasing operating frequencies, and existing methods fail to effectively reduce this charge through circuit means.
Innovation Solution
A driving circuit that divides the low-side transistor into a first and second low-side transistor, with the second transistor being smaller and delayed in shutdown, using a control circuit to manage their switching to eliminate reverse recovery charge.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the low-side transistor is turned off immediately after the high-side transistor is turned on, then the switching speed is improved, but reverse recovery charge accumulates at the drain terminal and base terminal, reducing power conversion efficiency
Solution Approach 1:
The low-side transistor is divided into two separate transistors: a first low-side transistor that handles the main current flow and a second low-side transistor that handles the reverse recovery charge removal. This segmentation allows each transistor to be optimized for its specific function, enabling the second transistor to be turned off later without causing simultaneous conduction issues, thereby eliminating reverse recovery charge while maintaining switching speed.
2Productivity
If the operating frequency of the power conversion circuit is increased, then the productivity is improved, but the impact of reverse recovery charge on efficiency becomes increasingly serious
Solution Approach 1:
The second low-side transistor is turned on before the first low-side transistor is turned off, creating an overlap period where both transistors are on. This preliminary action ensures that the reverse recovery charge is removed from the first transistor's terminals before the high-side transistor turns on, preventing charge accumulation even at high operating frequencies. The control circuit manages this timing to eliminate reverse recovery effects while maintaining high-frequency operation.
Data Source
AI summary
A driving circuit includes a high-side transistor, a first low-side transistor, a second low-side transistor, and a control circuit. The high-side transistor is coupled between an input voltage and a switch node. The first low-side transistor is coupled between the switch node and a ground. The second low-side transistor is coupled between the switch node and the ground. The control circuit periodically and individually turns on the high-side transistor and the first low-side transistor. After the first low-side transistor is turned off, the control circuit keeps the second low-side transistor on until the high-side transistor is turned on, so as to eliminate the reverse recovery charge of the first low-side transistor.