A customer developing switching power supplies and power electronics equipment faced a recurring failure: the auxiliary power IC U2 would fail immediately when the equipment was powered on.
Even though the surrounding components tested normally, the IC could not withstand the initial power-on event, resulting in repeated board failures and costly troubleshooting.
JEC Analysis
Our analysis identified the key issue: insufficient inrush current protection.
The original design lacked both an NTC thermistor at the input and an appropriate current-limiting resistor for the auxiliary power circuit.
JEC Solution
Adding a power NTC thermistor before the PFC stage to suppress the initial inrush current.
Adding a power resistor at the high-voltage input of the auxiliary power supply to provide additional current limiting.
The NTC and current-limiting resistor must be properly matched and positioned according to the circuit design.
After the solution was implemented, the power-on failure was resolved, improving the overall reliability of the customer’s power supply design.
Why JEC?
With extensive experience in NTC thermistors and circuit protection, JYH HSU (JEC) provides more than components. We support customers from component selection and sample testing to application-level solutions, helping engineers identify potential protection issues before they become costly failures.
Post time: Sep-07-2026