From: Fred Bloggs
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Subject: Re: V regulator input cap size?
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Date: Sat, 09 Nov 2002 03:58:24 GMT
NNTP-Posting-Date: Fri, 08 Nov 2002 19:58:24 PST
Organization: EarthLink Inc. -- http://www.EarthLink.net
John Fields wrote:
> On Thu, 07 Nov 2002 04:44:29 GMT, Fred Bloggs
>>Well if you insist on looking stupid then go ahead and optimize your
>>"reactive dropper." I had to place an order for some really cheap parts
>>so my entry probably won't be built until Wednesday, a 15 minute wiring
>>job. This is an HVAC application so the rule will be that you use a 40VA
>>24VAC NEC Class 2 power limited transformer- no rectifier transformers.
>>You will measure whatever it is you regulate at 0-25-50-75-100mA
>>loading, at line input of 95-115-135 VAC, and at -15 25 and 85oC. The
>>operation of the relay proves nothing for reasons I already mentioned-
>>it will be enough to substitute an equivalent load resistance- unless
>>you're using the coil in a way essential to circuit operation of course.
> The operation of the relay over temperature is critical to the
> success of the application and, consequently, can't be perfunctorily
> dismissed. Such being the case, I think the relay I found earlier
> on would be a good choice for us to use in this exercise, and I
> won't participate unless you agree to use it in your circuit, as I
> will in mine.
Fine- but since the properly chosen relay is designed to operate over
say -45 to 85 when the voltage developed across the coil is within
90-110% of nominal, then it makes no difference for purposes determining
successful circuit operation whether you use an actual relay or the
worst case loading equivalent of the coil.
> If you can't afford or don't want to buy one I'll
> send you one you can use since I've got to order some myself. Let
> me know what you want to do.
I can dig up a 12V , 300mW relay.
> In addition, the 75 and 100mA output
> current capabilities are high for the application and represent, for
> me, money badly spenty on unnecessary resources.
The original requirement was 12V all the way at 75mA maximum, with 30mA
for the two LEDs, 25mA for the relay, and 20mA for 12V circuit overhead.
I will allow you to off-load the 55mA for the LEDs and relay if you need
that, but the remaining 20mA has to be on 12V regulated. This was the
original requirement for which you suggested the "reactive dropper"- so
stick with it.
> That is, since the
> reactance of the series cap must decrease as the current required
> from the mains increases, dollars spent for unneeded extra
> capacitance are dollars wasted. Having said that, it seems a relay
> with a 300mW 24VDC coil would be a better candidate for this
> application. Wanna play that way, or do a one-off for the OP?
The essential requirement is that the circuit provide reliable power for
a 300mW coil relay. I was planning on a 12V relay and cannot use my
circuit topology for the 24V relay, that will be a major change and
eliminate many of the advantages. But it is okay if you want to use a
24V coil, the main thing is the 300mW power delivery either way, and I
don't see it preventing a basis for comparison of the two circuits.
A summary of the requirements is then:
1) provide continuous 300mW relay coil power- at any voltage you deem best;
2) provide 30mA of average LED current at continuous duty;
3) provide 20x12=240mW of regulated 12VDC output in addition to the
loading of items 1) & 2).