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NNTP-Posting-Date: Thu, 05 Dec 2002 14:15:48 -0600
From: email@example.com (John Fields)
Subject: Re: 24 VAC to 9VDC supply
Date: Thu, 05 Dec 2002 20:21:22 GMT
Organization: Austin Instruments, Inc.
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On Thu, 05 Dec 2002 19:24:45 GMT, "amdx" wrote:
> What do you think about my answer? Please don't hold back, don't be a
>wallflower or a shrinking violet. Tell me what you really think.
>Standing by in a underground lead lined room. :-)
>>You can use a series non polarized capacitor in the 24vac line.
>>Calculating the value is a bit more than just XsubL=Vdrop/current,
>>but this will get you close. I have used this when I didn't want the >heat
>of a dropping resistor.Capacitors used in speaker >crossovers have worked
The only thing I can see wrong with your answer is that you top
Actually, using a capacitor as a reactive voltage dropper is one of
my favorite ways to do it precisely because of the heat that _isn't_
generated. There was a lively thread (vreg input cap size) here a
couple of weeks ago about just that subject. You may want to check
it out on google if your news server no longer has it on.
Here's how I'd do it:
| | | | | |
24AC>--------|~ -|--+ [CR1] [C2] | [C3]
+----+ | | | | |
Where CR1 is a Zener used to keep the input to the 7809 from going
past the input limit if the load goes away.
Professional circuit designer
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