hello
I am designing a 8W isolated power supply to be integrated into an IOT design
I tryed to be inspired by the ref design of the UCC28911
please can you help me to optimize the size and validate my schematics and layout
best regards
This thread has been locked.
If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.
hello
I am designing a 8W isolated power supply to be integrated into an IOT design
I tryed to be inspired by the ref design of the UCC28911
please can you help me to optimize the size and validate my schematics and layout
best regards
Hi Ziad,
Thank you for the query on UCC28911.
Can you please let me know the primary magnetizing inductance so that I can review the scheatic? ALso please comment on the input voltage range.
Regards,
Harish
Hello
Thanks for your reply
we have 230VAC +-15% input voltage
for the moment i will be using the Wurth 750315369 or equivalent part
our application is OVCIII with degree of pollution 2 if it has any impact on the design
looking forward for your feedback
best regards
In addition i would like to measure the input AC voltage by the microcontroller in an isolated way in order to keep the galvanic isolation of my device
do you have any solution
best regards
Hi Zaid,
I have checked the schematic and it looks good.
Only couple of concerns, but nothing great. At 8W the peak current is close to 0.5A. So required Lm is 2*P/(Ipp^2*Fsw) which gives close to 750uH. Choosing 825uH is fine but might slight reduce Fsw when operating at full load.
The Cout choosen is 1.2mF. I suggest increasing it to 1.6 to 2mF based on transient requirement for a step load of 0.5A. If you need bigget step transients, say from 0 to 1.5A the capacitor will probably have to be 2.5x this value.
Ensure that R6 & R7 comes close to 29.35k, Maybe very slight tuning might be needed depending on performance at the time of testing.
I would suggest adding a resistor in parallel with snubber capacitor, close to 100k as this will help with the leakage reset quickly. Also have provision to connect a resistor and capacitor across the secondary diode as this will help cleaning out the aux winding waveform spikes.
For your question on isolated sensing, you will need isolated amplifier. The following app note will be helpful with the portfolio of isolated amplifiers and their application in isolated sensing.
In case you require any help with isolated sensing, please feel free to raise a post on this topic as it will be forwarded to the correct experts.
Please let me know if you have followup questions on the power supply.
Thank you
Regards,
Harish
Thanks Harish for your feedback
i updated the schematics, but i did not found where to put the 100K resistor ( on the 220V input or on the output capacitors ?)
i added a second 1,2mF capacitor since we are targeting 10 years life cycle
i changed the 430K resistor by a 1330K resistor to have a 29,33K equivalent resistor
i added a voltage and frequency measurement block, do you think it will works without impacting the isolation ?
once again thanks for the support
best regards
Hi Ziad,
Thank you for sending the updates to the schematic.
I think all the updates look good. The isolated voltage measurement should work.
I was referring to putting a 100k resistor across C2 if needed.
Please let us know if you have further questions.
Regards,
Harish
Thanks Harish for your support
In parallel my boss asked me to work on a miniaturized version of this power supply
do you have any solutions or hints to miniaturize it ?
best regards
Hi Ziad,
Thank you for the reply.
The following are the list of reference designs with UCC28911. You can check the layout to see which might suit you
TI might not have an equivalent product but these reference designs should be good place to start optimization.
Regards,
Harish
750371745r00 Prelim Spec Sheet.pdf
hello
i got this optimized flyback transformer proposal from wurth
please can you validate that it will work with the validated design ?
best regards
Hi Ziad,
Thank you for the reply.
The input voltage spec which you shared earlier is 230Vac with 15% tolerance. So assuming minimum close to 200Vac and minimum bulk voltage is close to 175V during operation, we can calculate Nps and Npa as follows:
Tr=2us, assuming Fsw=100khz, Dmax = 0.49 (approx)
Nps = 0.49*175/(0.413*(5+0.5)) = 37
Npa = Nps * (Vocc(min)+Vf)/(Vddoff+Vd_aux) = 37*(2+0.35)/(7+0.5)=12
So might want to double check on these. I see the Wurth transformer is specified for minimum 260Vdc. But bulk voltage could be much lower than that as per your specs.
Regards,
Harish