Field failures in PFC boost converters are among the most consequential — and most misunderstood — events in power supply and UPS design. When an IGBT fails, a capacitor ruptures, or a PCB trace burns, the instinct is to replace the part and move on. The right response is to ask why — systematically, every time.
The Cost of Not Finding the Root Cause
In power electronics, failure is rarely a one-off event. A converter that fails once — without a proper root cause investigation — will almost always fail again. The symptom changes, the timing shifts, but the underlying mechanism persists. This is especially true in PFC boost converter stages, which sit at the front end of power supplies and UPS systems and are exposed to the full harshness of the AC input environment.
Semiconductors and capacitors account for the majority of failures in power electronic products. But knowing which component failed tells you very little. The real question is what caused it to fail — and that answer almost always points back to something preventable: a design margin that was too thin, a thermal path that was insufficient, a component operating beyond its rated stress, or an application condition that was never considered during development.
"Replacing the part is not fixing the problem. Root cause analysis is not optional — it is the difference between a product that fails once and one that never fails again."
Three Methods for Failure Analysis
Structured failure analysis draws on three complementary approaches, each suited to different stages of the investigation:
In practice, effective failure analysis moves through all three — starting with what you can see, building to what you can replicate, and concluding with a model that explains and predicts. Skipping straight to model-based analysis without first understanding the physical failure is a common mistake that leads to incorrect root cause conclusions.
What Actually Causes PFC Converter Failures
Failure factors in PFC boost converters fall into two broad categories — internal and external — and understanding the distinction is essential for identifying root cause efficiently.
In the PFC stage specifically, the IGBT is a frequent failure point — not always because of a design flaw, but because of operating conditions that were never fully characterised. Third-quadrant operation during input transients, shoot-through conditions during switching, and thermal runaway triggered by elevated ambient temperatures are all mechanisms that can cause an IGBT to fail without any obvious design error being present.
A Structured Investigation Flow
The paper proposes a systematic failure analysis flow that can be applied to any PFC converter failure, reducing investigation time while increasing the probability of identifying the true root cause:
The Case Study Lesson
A real-world case study presented in the paper — involving concurrent IGBT failure, electrolytic capacitor failure, and PCB trace burning in a UPS PFC stage — illustrates how the structured approach cuts through apparent complexity. What looks like three simultaneous component failures is almost always a single initiating event followed by a cascade. Identifying the initiating event is the entire challenge — and the failure factor tables, applied systematically, make this tractable even under time pressure.
The conclusions from the case study reinforce a principle that applies broadly across power electronics: most field failures are predictable in hindsight. The stress conditions that caused the failure were present from day one. The failure analysis framework exists to make that visible before the product ships, not after it returns from the field.
For the complete failure factor tables, circuit-level and device-level analysis methodology, and full case study documentation, the paper is available on IEEE Xplore.