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Designing power supply with low output power

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Hello,

I have a project where I need to design a power supply that is connected to the grid (230Vrms, 50Hz) and has two output voltages. The grid's voltage isn't rigid and varies between 140-250Vrms.

My power supply should have 2 outputs with galvanic isolation:

- Output #1 supplies 24Vdc +-5% with a maximum current of 150mA.
- Output #2 supplies 5Vdc +-2% with a maximum current of 100mA.

Linear regulators aren't an option because of its low efficiency and the huge amount of heat it needs to dissipate. So switched mode power supplies are our only option.

What do you think is the best design to come up with?

2 buck converters with a 50Hz transformer on input? Flyback converter? Sepic?

Thank you
 

Fly back converter is the best solution for this low power(4.1W) application. Power integration having several multiple output design reference.
 
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    VSef

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STMicro also has the Viper series of-line flyback converters
 

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Yes, and the free PI Expert software on the powerint.com website can give you more options.
They even have a chip which can do it without an opto.....it has some internal method of pssing the feedback sig from pri to sec...not opto

- - - Updated - - -

however, your 5v is very tight at 2%, so i reckon you will need to give 100% feedback to the 5v rail, which leaves your 24v rail "flapping".
And then when the 5V rail goes into no load...and the 24V rail goes into full load, then you will get worse than 5% drop on the 24v rail...

so i reckon you will have to do a single 24V output, and get the 5v rail off that with a simple low power buck converter...ti.com do many, so do linear.com etc etc
 
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Thank you for your replies and sorry for my late reply.

I was thinking of using TI's UCC28910 which includes an integrated FET and uses primary sensing regulation (PSR) to regulate my output without the need for feedback. AUX is used to sense the output voltage. What do you think? Has anyone used this IC before and can share his experience?

however, your 5v is very tight at 2%, so i reckon you will need to give 100% feedback to the 5v rail, which leaves your 24v rail "flapping".
And then when the 5V rail goes into no load...and the 24V rail goes into full load, then you will get worse than 5% drop on the 24v rail...

so i reckon you will have to do a single 24V output, and get the 5v rail off that with a simple low power buck converter...ti.com do many, so do linear.com etc etc
Click to expand...

Adding another converter will add complexity and cost and I think I can live with a 5% tolerance on my 5V. Do you think a PSR type will be able to achieve such tolerances?

Thank you
 

5% on one output of a PSR converter is feasible, if the transformer design is good. But with multiple outputs it's very hard to say. I would read over this page: https://e2e.ti.com/blogs_/b/powerho...e-output-converters-with-primary-side-sensing

According to this, by stacking the multiple outputs in a certain way you can avoid some issues with multi output PSRs. However the outputs will not be isolated from each other. And they still show some poor regulation on the 12V output at light load.
 

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