Power Switching Order Control for Voltage Overstress Mitigation
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Solution Overview
Problem
Power converters, particularly those with parasitic bipolar transistors and flying capacitors, face voltage overstress due to excess stray inductance, leading to inefficiencies and potential damage from high transient power and excessive heat generation.
Innovation Solution
Controlling the switching order of power switches by transitioning them between on and off states at different times to mitigate voltage overstress, specifically by delaying the transition of one power switch in a pair to prevent parasitic bipolar transistors from turning on due to stray inductance, thereby minimizing peak voltage ringing across the flying capacitor.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If power switches are switched simultaneously to achieve efficient power conversion, then power conversion efficiency is improved, but voltage overstress occurs on parasitic bipolar transistors due to excess stray inductance
Solution Approach 1:
The patent applies preliminary action by transitioning the first power switch to off-state before the second power switch. This sequential switching arrangement ensures that the first switch is already in off-state when the second switch transitions, preventing the parasitic bipolar transistor from turning on due to voltage spikes caused by stray inductance during simultaneous switching.
2Reliability
If power switches are switched at different times to mitigate voltage overstress, then reliability is improved, but switching losses increase due to extended dead time
Solution Approach 1:
The patent applies parameter changes by optimizing the timing parameters of the switching sequence. The control circuit is configured to transition switches at specifically timed intervals that are sufficient to prevent parasitic transistor turn-on but minimized to reduce dead time losses. This involves adjusting the switching timing parameters to achieve the optimal balance between reliability and energy efficiency.
3Object-affected harmful factors
If stray inductance is reduced to prevent voltage ringing, then voltage stress on components is reduced, but device complexity increases due to additional circuit modifications
Solution Approach 1:
The patent converts the harmful effect of stray inductance into a beneficial outcome by using the sequential switching arrangement. Instead of attempting to eliminate stray inductance through complex circuit modifications, the invention accepts the presence of stray inductance and designs the switching sequence to exploit the timing characteristics, ensuring that voltage spikes occur when no switches are in the vulnerable off-state, thereby preventing parasitic transistor turn-on and minimizing voltage ringing effects.
Data Source
AI summary
An example method includes controlling a switching order of a plurality of power switches. The power switches are coupled to a flying capacitor and include parasitic bipolar transistors susceptible to the voltage overstress in response to excess stray inductance of the flying capacitor. The method further includes, in response to the controlled switching order, converting an input voltage of a first voltage level to an output voltage of a second voltage level while mitigating the voltage overstress of the parasitic bipolar transistors of the plurality of power switches.