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From: wte@ncrcae.Columbia.NCR.COM (Bill Eason)
Newsgroups: sci.electronics
Subject: Re: TTL to 1500 watts - query
Message-ID: <4582@ncrcae.Columbia.NCR.COM>
Date: 9 Jun 89 19:09:09 GMT
References: <1164@garcon.cso.uiuc.edu> <505@limbic.UUCP>
Reply-To: wte@ncrcae.Columbia.NCR.COM (Bill Eason)
Distribution: usa
Organization: NCR Corp., Engineering & Manufacturing - Columbia, SC
Lines: 41

In article <505@limbic.UUCP> gil@limbic.UUCP (Gil Kloepfer Jr.) writes:
>In article <1164@garcon.cso.uiuc.edu> kline@tuna.cso.uiuc.edu (Charley Kline) writes:
>>in the part that's going to have to take the delicate little TTL
>>signal from my shift register and use it to turn on and off a
>>1500-watt lighting instrument.  A mechanical relay is right out
>[...]
>>there's this thing called a triac which is essentially two SCR's
>>in parallel and facing opposite directions. I figure this is what
>>I want to use (but please correct me if I'm wrong). The problem
>>is that I have no idea how to connect this thing.
>
>A good (and my favorite way) to hook high voltage stuff to a low voltage
>circuit, like TTL, without the potiential of frying my TTL circuit is
>to isolate the two circuits using what is called an "opto isolator".
>This is a chip with a LED and phototransistor placed back-to-back.

Someone mentioned the Motorola MOC 3031, I believe, but I would like
to put in my $.02 worth on this.  Motorola has a whole family of these devices.
In my EE senior project, we used the MOC 3010 (I think), which is an
8-pin chip with a TTL-drivable LED on one side and a low-power-handling
triac on the other side.  The low-power triac can then be used to trigger
the gate on a high-power triac.  

Radio Shack sells the 3010 complete with their little circuit for this
setup on the back of the package.  One point to note, though, they give
two circuits: one for triggering an inductive load and one for a resistive
load.  We were controlling the power to a 500W slide projector bulb, and
I believe we used the circuit for a resistive load.  You may want to check
this if you decide to go this route.  A little extra circuitry (which
we used, too) will let you control the percentage of power to the bulb
instead of just turning it full-on or full-off.  A little more circuitry
will let you control this from a digital value (8 bits = 256 brightness
levels).  Email for more info.

-wte

-- 

Bill Eason   (803) 791-6419    ...!ucbvax!sdcsvax!ncr-sd!ncrcae!sauron!wte
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