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From: jans@mako.UUCP (Jan Steinman)
Newsgroups: net.analog
Subject: Re: AC current monitor
Message-ID: <670@mako.UUCP>
Date: Thu, 28-Mar-85 13:53:29 EST
Article-I.D.: mako.670
Posted: Thu Mar 28 13:53:29 1985
Date-Received: Sun, 31-Mar-85 02:39:36 EST
References: <5139@fortune.UUCP> <445@umd5.UUCP>
Reply-To: jans@mako.UUCP (Jan Steinman)
Distribution: net
Organization: Tektronix, Wilsonville OR
Lines: 39
Summary: 

Here's one I cooked up for turning all the bits and pieces of my computer on
whenever I turn on the desk lamp.  It's independent of power level (up to the
current rating of the rectifiers), has a moderate, but constant drop (~3.0
volts), has no moving parts, and uses readily available parts.  (Radio Shack
variety)
			Bridge Rectifier
			+-------+
			|  BR1	|
	o---------------+~     ~+------------------o
	Line		|  +  -	|		Load
			+-------+	+-------+
		+----------+---|--------|+     +|------o TTL current sink
		|	   |   |	|	|
		|	D1 v   |	|  IC1	|
		|	   -   +-\/\/\--|-     -|----+
		|	   |   |   R1	+-------+    |
		|	D2 v   |		     v TTL system ground
		|	   -   |
		|   C1	   |   |
		+---)|-----+---+

The bridge rectifier, D1, and D2 should have a current rating greater than the
the maximum load current.  BR1, D1, and D2 should have PIV ratings of at least
250 for safety.  C1 is not critical: 1uf @ 5VDC will do.  R1 should be chosen
to provide the needed current to the opto-isolator IC1, 180 ohms should do.

Most LEDs (like the type used in opto-isos) have a threshold of about 1.3
volts, therefore two silicon drops (D1 and D2) are required in order to get
the opto-iso to fire.

I used a MOC3010 opto-iso (which has a triac output) to trigger an 8 amp
triac and built the whole thing INSIDE a Radio Shack outlet box.  Different
opto-isos provide simple (or darlington) open-collector outputs.

This circuit works reliably from miliwats up to the current limit of the
rectifiers, 20 amp bridges and rectifiers are not uncommon or expensive.
-- 
:::::: Jan Steinman		Box 1000, MS 61-161	(w)503/685-2843 ::::::
:::::: tektronix!tekecs!jans	Wilsonville, OR 97070	(h)503/657-7703 ::::::