Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!asuvax!ncar!boulder!ccncsu!ncr-fc!mikemc From: mikemc@mustang.ncr-fc.FtCollins.NCR.com (Mike McManus) Newsgroups: sci.electronics Subject: Re: Switching from 5V to 120V Message-ID: Date: 27 Feb 90 17:53:08 GMT References: <3709@uceng.UC.EDU> <801@gold.GVG.TEK.COM> Sender: news@ncr-fc.FtCollins.NCR.COM Distribution: na Organization: NCR Microelectronic Products, Ft. Collins, CO Lines: 46 In-reply-to: grege@gold.GVG.TEK.COM's message of 22 Feb 90 17:49:19 GMT In article <801@gold.GVG.TEK.COM> grege@gold.GVG.TEK.COM (Gregory Ebert) writes: > In article <3709@uceng.UC.EDU> dmartin@uceng.UC.EDU (Dale Martin) writes: > > > >I have designed a circuit using ttl logic chips that activates LEDs. I would > >like it to activate some 25W bulbs (one at a time). What is the best approach? > >Could I use relays, or is the switching voltage too low? How about a transis- > >tor? Aren't there triacs or something that do just that? > >ANY suggestions would be appreciated, the more specefic (part #'s and such) > >the better. > > > There are a few things you can do. First of all, you CAN have common > ground for the TTL and the 120 VAC bulbs if you are CAUTIOUS. If > you are willing to hunt around, you can get some opto-triacs. This > is obviously the safest way to do it. An opto-triac's control side > is just an LED, so you have that one licked. The other side is > basically like a relay contact if you run it on AC or pulsed-DC. > You should put an inductor in series with the light bulb to > protect the triac from 'di/dt' problems. A 10uH coil will give > you protection up to a di/dt of ~20A/usec (reasonable) for 120VAC. > If you use a larger coil, thats OK. Radio Snack sells some $0.79 > coils that are perfect. These beasties are actually VERY easy to work with, but they are a bit pricey (expect about $10 a pop, which I realize can be an issue for a student :-). They come in various flavors: AC output, DC output, DC input, and (I would guess) AC input. They are often refered to as "solid-state relay modules" or "I/O modules", and most often used in micro-processor based industrial controls and such (at least that's where I've seen them). They are small (about the size of a deck of cards) and modular: can plug in and out of an appropraiate socket. I've even seen boards sold which connect up to PC's and allow about a dozen or so modules to plug in for PC-based control systems. If you decide to go the SCR route, I would still suggest using opto-couplers to the input. This will isolate your TTL stuff from the nasty AC environment. This will help out in the "noise" department (trust me, you *DON'T* want to debug a system which has noise problems!). Good luck! -- Disclaimer: All spelling and/or grammer in this document are guaranteed to be correct; any exseptions is the is wurk uv intter-net deemuns. Mike McManus (mikemc@ncr-fc.FtCollins.ncr.com) NCR Microelectronics 2001 Danfield Ct. ncr-fc!mikemc@ncr-sd.sandiego.ncr.com, or Ft. Collins, Colorado ncr-fc!mikemc@ccncsu.colostate.edu, or (303) 223-5100 Ext. 360 uunet!ncrlnk!ncr-sd!ncr-fc!garage!mikemc