first, sorry about my english.
Currently I'm working as project engineer developing an AC/DC power supply. The AC section is a resonant flyback and diode rectify to get 48VDC. With these 48 volts and 4 MAX17506 DC/DC buck controller, I obtain four 5VDC/3Amps outputs. Next picture is brief of my circuit.
simulate this circuit – Schematic created using CircuitLab
As you can see, I rectify using a pairs of diode and clamping the voltage with two zeners, next a ten units of MLCC murata capacitors (2.2uF/100V X7R C1206) and single electrolytic cap (2200uF/63V). Following, four DC/DC buck converter using the MAX17506 IC. This it's working fine, but in several units the MLCC caps (caps before electrolytic) was literally blown to pieces. Things tested:
- Voltage capacitors are OK, 100 volts.
- No overcurrent and no overtemp.
- No shortcircuit.
- The polarity of electrolytic cap it's OK
The only clue about this mystery is what the electrolytic capacitor always be BEFORE MLCC caps, not after.
Any idea?
I'll add more info. The failure occurs in cold start, attached pic.
the gray thing is Polyurethane Resin