Power Switching Circuit Body Diode Conduction Reduction
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Solution Overview
Problem
High switching speed and current switching circuits face performance degradation due to parasitic body diodes, leading to increased switching losses, EMI, and noise, with existing solutions like Schottky diodes and adaptive gate-drive techniques having limitations in availability and complexity.
Innovation Solution
A power electronics switching circuit is enhanced with a delay function to prevent significant current flow through the internal body diode, using a first switch for current flow, a second switch for return, a third switch to prevent body diode conduction, and a free-wheeling diode for alternative conduction paths, controlled by a switch controller with a timing margin.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high switching speed and current switching circuits are used, then productivity and power conversion efficiency are improved, but parasitic body diode conduction causes increased switching losses, EMI, and noise
Solution Approach 1:
The circuit proactively prevents body diode conduction by using the third switch to block current flow before it can reach the body diode. The delay function also provides preliminary timing control to ensure the second switch turns off before the first switch turns on, preventing shoot-through and body diode conduction in advance rather than attempting to mitigate effects after they occur.
Solution Approach 2:
The third switch acts as an intermediary element inserted between the power source and the second switch. This intermediary component specifically blocks current paths that would otherwise flow through the parasitic body diode, while the free-wheeling diode serves as an intermediary that provides an alternative current path during transition periods.
2Reliability
If dead time is increased to allow current transition from body diode to Schottky diode, then body diode reverse recovery effects are reduced, but switching losses increase and high frequency operation becomes unacceptable
Solution Approach 1:
The invention extracts and removes the problematic body diode conduction path from the circuit operation by using the third switch to block current flow to the body diode. This eliminates the need for extended dead time to manage body diode reverse recovery, as the body diode is prevented from conducting in the first place.
Solution Approach 2:
The delay function provides preliminary timing control that ensures proper switch transition sequencing. By delaying the turn-on of the second switch until after the first switch has turned off and current has transferred to the free-wheeling diode, the circuit prevents body diode conduction without requiring extended dead time periods.
3Loss of energy
If a third switch and delay function are added to prevent body diode conduction, then switching losses and EMI are reduced, but device complexity increases
Solution Approach 1:
The third switch is merged with the existing switch structure, sharing common terminals and integrating into the power stage without requiring completely separate circuitry. The delay function is merged with the control logic, combining timing control with the existing switch controller functionality.
Solution Approach 2:
The third switch serves multiple functions: it blocks body diode conduction, provides an additional current path control element, and works in conjunction with the free-wheeling diode to manage current transitions. The delay function provides both timing margin for shoot-through prevention and coordination for body diode conduction prevention.
4Loss of energy
If adaptive or predictive gate-drive techniques are used to reduce body diode conduction time, then switching losses are reduced, but controller choice is limited and shoot-through protection may be inadequate
Solution Approach 1:
The circuit uses predetermined timing delays and switch sequencing to proactively prevent body diode conduction and shoot-through conditions. This open-loop timing control approach is more universally applicable than adaptive or predictive techniques that require specific controller capabilities, while still achieving reduced switching losses.
Solution Approach 2:
The third switch acts as an intermediary that provides robust shoot-through protection regardless of controller timing precision. This additional hardware layer of protection complements the timing control and ensures safety even when controller capabilities vary.
Data Source
AI summary
A circuit for minimizing the effect of a parasitic body diode by combining a power electronics switching circuit with a pinch-off switch and a delay function.