I have had issues in the past with using too close of an input power supply to the max rating of my main power regulator causing failures. For example, I used a 24VDC supply with a regulator with an absolute max rating of 28VDC. When this PCB was used with a PSU with a long cord, there would apparently be an inductive power spike upon turn on, that would destroy the regulator. The PCB had a 0.1uF ceramic cap on the input line parallel with a 47uF electrolytic cap. The chip also had a 0.1uF ceramic on each input pin. So obviously this inductive spike was a long event, as my capacitance should work for short spikes.
I now am working on another project that I don't have any options to go with a higher rated regulator. I have a 15VDC input supply with a chip with a max rating of 24VDC, recommended 20VDC. This system will be using a long (~6') cord.
What are my options to condition the input supply? A bad solution that I thought of, was to buffer with a linear regulator before this chip, that would only drop a small amount of voltage, but would be rated higher..
Do I just need more bulk capacitance? Something like 100uF+? The switching regulator will be going from 15VDC to 17VDC at up to 15A. Switcher: MP3428AGL-Z
EDIT: Some clarification:
- Power cord length is from the PSU -> PCB
- On old PCB, when the PSU was plugged into the PCB and then the PSU was turned on, the regulator would blow. When the PSU was turned on, then plugged into PCB, it would be fine. So the inductive spike was from the initial inrush current.
- New PCB has different PSU, much higher quality, so it shouldn't be an issue, but I want to plan for the worst case, as this is an important design.