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Subject: Re: PSU Design Q - 115/230 VAC Protection
Date: Tue, 3 Sep 2002 01:45:47 +0800
Organization: IMS Netvigator
X-Newsreader: Microsoft Outlook Express 6.00.2600.0000
something called VDR may help you.
when voltage goes beyong desired value, it simply broken into short circuit
and blown the fuse.
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> Hi all,
> I'm designing a linear power supply which is required to operate on
> both 115 VAC and 230 VAC (for both USA and Europe). I'm using two
> toroidal transformers, each with 2 x 115 VAC primaries. I'm planning
> to use a mechanical switch to connect the primaries in series/parallel
> according to the input voltage required (230/115 VAC).
> What I would like to do is to protect the unit in case someone
> accidentally switches to the 115 VAC setting and plugs the unit to a
> 230 VAC mains. What is the "standard" way to do this? I was thinking
> of putting the usual fuse in the mains line and put Zener diodes
> (connected anode to anode) across each of the primaries so that if the
> voltage across each winding exceeds say 150 VAC the fuse will blow.
> The Zener voltage would then be:
> Vz = 2 * 1.414 * 150 VAC = about 425 V
> I may need to put a few Zeners in series to achieve this voltage. Is
> this a good way to do it? I've never done anything like this before,
> so I want to be sure. What do you guys recommend? Also, if the above
> method is OK, what kind of Zener should I be using (in terms of Watts
> and other specs)? Are there any special devices that are more suitable
> for this purpose?
> Many thanks in advance.
> PS: You may have seen this before, sorry for the double posting but my
> ISP's news server appears to be in limbo... Posting this using Google.
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