buck dc-dc converter 230V-100V DC

[miu86]

hy guys I'm trying to build a dc-dc buck converter that lowers the voltage from 230V DC (230 AC wil be rectified with a full-bridge) to 100 V Dc and I=16mA. For the sw I'm thinking of a MOS-Fet IRF9640 but i'm having some difficulties with the PWM signal in the G and also powering it. Could use LM555 or TL5001. These need a smaller input voltage and I need a optocoupler to obtain that voltage? 5V:50V . It's confusing :roll:.
Thank you

 

[ted]

Hi,
First, please note, that when you rectify 230V AC, you will get up to approximately DC = 1.4 x the input AC voltage. Thus, you start from 320V, not 230V DC.
Therefore, I would recommend, that for instance the filtering capacitors should be at least dimensioned for 350V, and everything else accordingly.
Secondly, if you rectify directly from the mains lines, your system will be in a lethally high voltage against ground. You have to be careful, and consider safety aspects. A buck converter is not isolated. Therefore your 100V output would be also in a dangerous potential.

I would rather recommend an isolated converter solution. That way only the primary side would be in a lethal potential, and your output side would be relatively safe (100V can hurt, too!).

From your questions I get an impression, that you aren't very experienced. Therefore I wanted first to mention safety, before proposing any other parts of a solution.

In addition, provided, that you can handle the safety aspects, the easiest approach is to use a controller chip, which is intended for power supplies directly from rectified mains voltage. From the suppliers you will also get a reference design, so you don't need to re-invent everything.

For instance Texas Instruments has many solutions for such a converter, and many of their control chips are pretty cheap and relatively easy to use. Linear Technology has also many nice components, but they tend to be slightly more pricey. There are very many other companies in that business, too many to list here.
Do not worry too much, if the output of the reference design is much lower, than what you need. It is in general not too difficult to change. Especially that applies to situations, where the control circuitry is nearly entirely on the primary side.

In some cases you might have use for a lower "auxiliary" output voltage, for the output feedback circuitry, because "taking" the optoisolator current from 100 V might cause unnecessarily high losses.

I would recommend, that you search web sites of Texas Instruments and Linear Technology, and study their reference circuits and parts. Also Google is a quite useful tool. too.

 

[treez]

also you don't say what power level.
If low power , then the linkswitch (LNK302?) from powerint.com can be for you.
powerint.com have software you can use to design your whole system if you wish

 

[miu86]

Thanks for the replay, I will redimension everything according to 350V.
You are right about the experience part, I know that it will not be protected but it will be smaller in size and dimensions are an issue and also costs. I will look for controller chips on thes websites and try to go withe the buck for now. Thank you

 

[miu86]

This is the schematic I'm thinking off,
I saw something on powerint.com using LNK 304 like this can I modify it to my needs of 100 V Dc and 16mA?

 

[treez]

ill have to look at lnk304 datasheet.

 

[miu86]

please take a look and tell me what you think :smile: