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Old 28th January 2003, 08:59 AM   #1
DJG is offline DJG
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Question Mini Switcher - about 500mA

Hello!

I need a schematic for a mini switcher with a few components only. It has to be powered by AC 220V in has to produce DC 12V.
It will be used as PSU for one relay and IC 4027. I supose that 500mA should be enough.
Does anyone have an idea how should this be done? I was hoping that i could use an IC, but i'm not sure that it is possible.

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DJG
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Old 28th January 2003, 06:49 PM   #2
alvaius is offline alvaius  Canada
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For a relay and a single gate, you probably need more like 20 mA, not 500. Just buy the smallest transformer you can find or buy a small AC\DC power supply. ST has a linear regulator that I believe you can get 20mA out of. Designing a switcher for AC use is just not worth it at low volumns.
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Old 28th January 2003, 07:38 PM   #3
DJG is offline DJG
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Would you perhaps know the exact label of that ST? Or do you might have a schematic of it?

thx
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Old 29th January 2003, 02:46 PM   #4
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National Semiconductor LM2954 series of "Simple Switchers" will work great for your application.
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Old 29th January 2003, 08:38 PM   #5
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No, it wont. disregard that last post. I forgot about your 220V input requirement.
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Old 29th January 2003, 08:40 PM   #6
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Try making a Royer Converter from the rectified AC line. It would require a transformer with a primary, a secondary, and two aux windings. Also, two resistors and two transistors. Your transformer should be a "square" B-H material such as Permalloy 80 or Orthonol. Good Luck!!
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Old 29th January 2003, 08:52 PM   #7
Helix is offline Helix  United Kingdom
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what about one of these ?

http://www.futura-shop.com/pdf_eng/1350-VB409SP.pdf
- only about 30 mA tho
Or

You can use a cap. to reduce mains voltage.


Be careful with mains plz
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Old 30th January 2003, 07:17 AM   #8
DJG is offline DJG
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Yes, this VB409 is the right thing for me!

-Just one question - where to buy?
I looked over all the shops in Slovenia, but they don't have it

DJG
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Old 30th January 2003, 01:03 PM   #9
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If you are only driving a relay and a mini IC, it would be best to just use a low frequency main transformer with rectifier and cap filter. The previously mentioned part will dissipate huge amounts of power and will require a heatsink. Also the minimum output current on this part is 80mA much higher than your required minimum. You may have trouble there.
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Old 30th January 2003, 06:40 PM   #10
DJG is offline DJG
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I don't know... I realy don't want to use a transformer.
I guess I'll have to ask directly: How should I build a button-switch, witch would control 1kW toroidal trans.?

DJG
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