Dear Team,
We have developed an 900W Charger using UC3846 IC.
The key specifications are,
- Input : 180V to 280V AC
- Output : 60V@15A
- Ta : 0°C to +50°C
Topology is Half Bridge. No PFC circuit is used.
The units are working fine but there is a serious problem also. Of course this is a conflicting statement and I will explain here.
Problem details
The units are randomly failing during any of these conditions,
- During AC Switch ON at any load (the load connected can be - No Load, Full Load or any load between No Load to full Load).
- During the Output Load connection or disconnection.
Failure Mode :Majorly only Mosfets will fail. Simply replacing the Mosfets the unit MAY work fine.
Why I mentioned above as working fine is, sometimes the same unit may fail 3 times but after changing the Mosfets it may work continuously without any failure (like this we have around 8 Chargers which have been working for the last 4 months without any failure).
Corrective Action : We have done few corrections as mentioned below and the problem is drastically reduced but completely not resolved,
- The DC blocking capacitor value is increased
- One ground correction is done in Gate Drive circuit
Before these corrections, if we test 10 units around 8 units were failing. The same unit also may fail multiple times.
After the above corrections, if we test 10 units around 3 units are failing.
Suggestions required
Please suggest us where can we work to resolve this issue,
- Is Gate drive optimisation required?
- How to choose the proper DC blocking capacitor value.
- Any good document on the grounding.
Best Regards,
J.V. Siva Rama Rao
+91-81215-00889
