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adapter-12v/60w Design Issues

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mak.goel

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Hello to All,
I am working on a design of adapter as per below specs,
Input voltage : 100V-300VAC
Output : 12V/60W (Continuous running at 50deg ambient)
Cabinet : Closed frame (ABS/Plastic) same as normally adapters have

Briefing on my design:
PWM IC controller -- UC3845, Mosfet – IPP65R190CFD,
Schematic and BOM will be shared during further correspondence.
With this design, temperature at multiple places like magnetics, mosfet, output diode and snubber is reaching to 120-125 deg & finally resulting to failure in 3-4 hours operation.

I am looking for your expert advice to move in very right direction for adapter design. No problem even if I need to change my topology to reach on right place.
Kindly advice,

Regards,
 

Try a resonant LLC topology HB in ZVS.
That offer better efficiency.
Need a good controll design and output overvoltage protection to protect load in case of any failure in controll circuit.
 

Hi,

With this design, temperature at multiple places like magnetics, mosfet, output diode and snubber is reaching to 120-125 deg & finally resulting to failure in 3-4 hours operation.
Sounds like a unsuitable thermal concept:
* either too high power dissipation: use devices with less power dissipation
* or small heat spreading, reduced airflow, unsuitable PCB layout: --> modify PCB layout, use heatsink, heat spreaders, fan, potting compound with good thermal conductivity...

Klaus
 

fan in closed frame... its fun)
2TS:
sync rectifier is good decision for 12v output for efficiency increasing
maybe try quasiresonant flyback - you can gain better efficiency
but LLC with sync rectifier is topology for best efficiency, i think
 

Thanks every one for responding !!

Natural cooling only needs to be adopted for this concept.

Can anybody share some reference design to move further on a right path ??


Regards
 

With this design, temperature at multiple places like magnetics, mosfet, output diode and snubber is reaching to 120-125 deg & finally resulting to failure in 3-4 hours operation.
Agree with post #3. If the case temp reaches 125ºC, then you are close to the max junction temp. Is 125ºC case temp according to your design ?
Improving heatsinking might make it work.
 

We have designed plenty of adapters for industry - it is a major task to get good operation at 50C external ambient.

Sounds like you have a flyback controlled to give good power factor - it should also be resonant to keep losses down of the pri side (and meet EMC) and the Tx needs to be extremely good coupling to take away your snubber problems - also synch rect of the output is essential for 50C ambient...

good luck ...
 

Thanks again to everyone !!

I got few ideas with your posts/comments.

However, reference design if can be shared would more help to us.

Regards
Mak
 

Hi,

However, reference design if can be shared would more help to us.
(Almost) Every SMPS IC manufacturer provides reference designs, design notes, application notes, online calculators...

Klaus
 

Respectfully there are very few, if any, reference designs that will get you near operating in a sealed plastic box at 50C external ambient, with a 60W load at 100VAC in - what you seek is, in reality, a major design exercise in disguise...
 

Hi ,

Please check if snubber design is correct. Please share waveform of VDS. Which transformer is used?
 

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