dmartin@uceng.UC.EDU (Dale Martin) (02/22/90)
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. Thanks! _______________________________________________________________________________ To the beautiful and the wise, | dmartin@uceng.uc.edu the mirror always lies. -Rush | -Dale Martin -------------------------------------------------------------------------------
cook@stout.ucar.edu (Forrest Cook) (02/22/90)
I would suggest looking into solid state relays. They are optoisolated
triacs with some additional goodies inside. Your circuit can drive the
led inside of the SSR without any changes and the SSR does the dirty
work. They can be had new in the $10 to $50 range depending on how
much power you want to control. Surplus electronics stores often carry
them for a few bucks each.
^ ^ Forrest Cook - Beware of programmers who carry screwdrivers - LB
/|\ /|\ cook@stout.ucar.edu (The preceeding was all my OPINION)
/|\ /|\ {husc6|rutgers|ames|gatech}!ncar!stout!cook
/|\ /|\ {uunet|ucbvax|allegra|cbosgd}!nbires!ncar!stout!cookhenry@utzoo.uucp (Henry Spencer) (02/22/90)
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? Relays are possible, but the best way (my opinion) is to use a 3011 or one of its relatives -- an optoisolator with a small triac as its output -- to drive a larger triac. The 3011 datasheet (from, e.g., Motorola) goes into how. This gives you silent, fast, precise switching. The larger triac can be pretty generic, although it's nice to get an insulated-case type so your heatsink isn't electrically hot. -- "The N in NFS stands for Not, | Henry Spencer at U of Toronto Zoology or Need, or perhaps Nightmare"| uunet!attcan!utzoo!henry henry@zoo.toronto.edu
grege@gold.GVG.TEK.COM (Gregory Ebert) (02/23/90)
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. The other way is to use standard SCR's (avail @ Radio Snack). The solution has 2 parts : (1) You need to get the +5 volt and 120 VAC supplies to the same ground, and (2) Drive the lamps. SCR's will conduct for only 1/2 cycle (versus full cycle for triacs), so you will want to switch to 50W bulbs. The advantage is that SCR's have a simpler gate-drive circuit. The cheapest way is to use the standard transformer/bridge/capacitor supply for your +5 volt stuff, and connect it to the neutral side of the AC line. Before I get flamed, I want you all to know that I have done this for years and I'm still alive. You have to be careful about using test equipment such as scopes, etc. As long as you dont put 120 VAC a-c-r-o-s-s TTL, all is fine. An SCR's gate can be driven by TTL with a 100 ohm resistor in series. If your SCR has a lower gate current, say 1-5 mA, use a 1K. The SCR anode is connected to one side of the light bulb. The other side of the light bulb is connected thru a 10uH coil to the HOT side of the AC line. I strongly suggest you use a fuse. The cathode of the SCR connects to the ground of the TTL supply AND the neutral side of the AC line. If you switch the hot and neutral wires, the beastie will still work, but if you accidentally touch the circuit 'ground' you might get surprised !. One point worth mentioning here is that the NEUTRAL wire is physically tied to the earth near your KW-hr meter, so you can PRESUMABLY touch it without getting shocked. BUT !!! there will be voltage drops throughout your house wiring along this line due to resistive and inductive effects, which can result in dangerous voltages with respect to ground, so be careful. The last, and most expensive, way is to use an isolation transformer and hook the rest up as detailed above. Now you dont have to worry as much about getting shocked if you always remember to touch only one circuit node at a time.
kenny@m.cs.uiuc.edu (02/24/90)
Henry Spencer writes: >Relays are possible, but the best way (my opinion) is to use a 3011 or >one of its relatives -- an optoisolator with a small triac as its output -- >to drive a larger triac. An alternative to this is something along the lines of a Potter & Brumfield OA16-66, which has a one-amp triac on board -- more than enough for the 25-watt load that the original poster envisioned. It's in a 16-pin DIP, and needs a heat sink, but the package is insulated. 5-volt relays still have the optoisolator approach beat if parts cost is the major issue, but are slow to switch, noisy (both acoustically and electrically), tend to fry driver transistors, and tend to fail at the crucial moment. I agree with Henry about optoisolators. Kevin KE9TV
mikemc@mustang.ncr-fc.FtCollins.NCR.com (Mike McManus) (02/28/90)
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