Author Topic: non-isolated AC/DC buck converter with no transformer for microcontroller  (Read 4644 times)

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Offline srinivas

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Recently While breaking into a Industrial controller i came across Microcontroller board that was 230 vac input and had No-Transformer or inductor which was quiet new to me. The AC input  was filtered, rectified and then  through a D-PAK pakage (some kind of requlator ??) and then through several diodes and resistor which then powers the microcontoller.

How does it work???
Is it an efficient Design (especially for industrial use)to be used with microcontroller circuits.
 

Online mikeselectricstuff

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Re: non-isolated AC/DC buck converter with no transformer for microcontroller
« Reply #1 on: December 31, 2013, 01:41:07 pm »
There are several ways to do it. Power integrations do a number of chips (LNK30x series).
Are you sure there was no inductor?
For very low currents it could even be a linear regulator.
It would be feasible to have a microcontroller that stops running when the line voltage is high to reduce dissipation.
Another approach is to have a high voltage switch that turns off when the voltage in each cycle exceeds a certain level.


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Offline tszaboo

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Re: non-isolated AC/DC buck converter with no transformer for microcontroller
« Reply #2 on: December 31, 2013, 02:26:21 pm »
If you know that the used current will be low, you can make a very crude supply voltage with a 5V zener diode with capacitive coupling/dividing. Teacher of my at university was suggesting this. It is not efficient, nor nice, nor safe so finally I did not used the design.
They discuss it here:http://electronics.stackexchange.com/questions/41938/230v-ac-to-5v-dc-converter-lossless
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Offline mariush

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Re: non-isolated AC/DC buck converter with no transformer for microcontroller
« Reply #3 on: December 31, 2013, 02:33:28 pm »
Maybe it was a simple capacitive dropper power supply  (use a capacitor and resistor to go down to about 10-30v then use a linear regulator? )

See this appnote : http://ww1.microchip.com/downloads/en/appnotes/00954A.pdf
 

Offline LukeW

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There are a couple of different options.

If you only want a very small amount of current (like say <50mA) you can use the classic transformerless capacitive dropper approach with a large polymer capacitor, zener diode, rectifier diode etc.

Or if you need a little bit more power (say 3-5W) you can use chips such as the NXP TEA1721 or Power Integrations LNK30x which are basically just buck converters with a very high voltage DC input, and some basic rectification and filtering of the mains to yield 340V DC or so (less if you have 110VAC) going in to the chip. These sorts of chips will give you a little bit more power that is just not practical with a RC "dropper" in a transformerless circuit, and they'll be much smaller and more efficient and won't dissipate heat, as well as working with universal 90-260VAC input.

In this thread I discuss a basic example circuit which uses a LNK304 for exactly this sort of job.

https://www.eevblog.com/forum/projects/lnk304-smps-design/
 


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