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From: "Leif H"
Subject: Re: Howto: Low current PS without a transformer
Date: Thu, 14 Nov 2002 08:26:45 +0100
NNTP-Posting-Date: Thu, 14 Nov 2002 07:35:40 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
I had hoped that some new semiconductors had come that would make the
transformer obsolete. My budget for the PS is about $2 and the transformer
would take almost the whole budget.
I am not concerned that the user can touch the high voltage electronics and
hurt himself since the electronics I am developing is connected so close to
the mains that he might as well touch the main as the second side of a
transformer. So transformer or not does not much difference in this aspect.
Does anybody know how a light dimmer is made? Does it need some low voltage
"John Fields" wrote in message
> On Tue, 12 Nov 2002 10:44:06 +0100, "Leif H" wrote:
> >I need a simple and cheep power supply that I can connect to 220V AC. How
> >can I make this without using a large and "expensive" transformer? The
> >output voltage is about 3V DC and the current is less than 50mA. Any
> You could do this, but it's not isolated from the mains so if
> there's the remotest possibility that the user could come in contact
> with _any_ part of the circuit they might be killed.
> Best bet would be to get a small, inexpensive transformer and do it
> that way.
> If you want to do it this way, post back and I'll put in some
> component values for you.
> 220>--+-[CR1>]-+-[ | | | LM317
> | +------------+-----+---IN OUT--+---+-->>--+
> | | | | GND | | |
> +--+ | | | [R1] | |
> | | | | | | |
> | [CR5] [C2] +------+ [C3] [RL]
> | | | | | |
> | | | [R2] | |
> | | | | | |
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