Parallel Bipolar Transistor Switching for Lower Reverse Recovery Loss
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Solution Overview
Problem
Bipolar transistors and diodes in power electronics experience significant conduction and switching losses due to reverse recovery processes, leading to inefficiencies and increased energy dissipation, especially when operating at currents below their rating.
Innovation Solution
A circuit design that strategically switches on and off groups of bipolar transistors and diodes in a controlled manner, with specific subgroups being activated and deactivated at different times within a switching cycle to minimize losses, optimizing chip size and reducing reverse recovery charges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If a device with high current rating is used to ensure sufficient current capability, then the device can handle high currents, but the reverse recovery charge increases leading to higher losses at low currents
Solution Approach 1:
The patent divides the bipolar transistor circuit into multiple parallel-connected transistors (first subgroup and second subgroup) with different current ratings. This segmentation allows the system to use smaller, more efficiently-rated devices rather than one large over-dimensioned device, reducing reverse recovery losses while maintaining sufficient current capability.
Solution Approach 2:
Different transistors are assigned different current ratings appropriate to their specific function and operating conditions. The first subgroup transistors have one current rating optimized for their operating conditions, while the second subgroup transistors have a different current rating, allowing each device to operate near its optimal point rather than all devices being over-dimensioned.
2Productivity
If bipolar transistors are switched on and off in a conventional manner, then the circuit operates, but significant switching losses occur due to reverse recovery processes
Solution Approach 1:
The patent applies preliminary action by switching off the first subgroup transistors before the second subgroup transistors during the switching cycle. This sequencing allows the circuit to prepare for the next state in advance, reducing the overlap between voltage and current during switching transitions and minimizing reverse recovery losses.
Solution Approach 2:
The patent implements periodic switching of the bipolar transistor subgroups with optimized timing. By periodically switching the first subgroup off before the second subgroup, and maintaining this rhythmic pattern, the system reduces switching losses while sustaining productive operation.
3Device complexity
If all bipolar transistors are switched off at the same time, then the switching control is simple, but the reverse recovery charges cause increased power losses
Solution Approach 1:
The patent segments the bipolar transistors into two subgroups with different switching timings. This segmentation requires more complex control circuitry but enables optimized switching sequences that reduce reverse recovery losses and improve overall efficiency.
Solution Approach 2:
The patent introduces dynamic switching control where the switching timing of different transistor subgroups is differentiated. The first subgroup is switched off at a different time than the second subgroup, creating a dynamic switching pattern that reduces power losses compared to simultaneous switching.
Data Source
AI summary
A circuit includes a transistor circuit including a first node, a second node, and a plurality of transistors coupled in parallel between the first node and the second node. The circuit further includes a drive circuit configured to switch on a first group of the plurality of transistors, the first group including a first subgroup and a second subgroup and each of the first subgroup and the second subgroup including one or more of the transistors. The drive circuit is further configured to switch off the first subgroup at the end of a first time period and switch off the second subgroup at a time instant before the end of the first time period.