A reversed transistor array?

kiltjim · 11-09-2005, 09:30 PM

I'm not an EE, so I know what I want, but I don't know the easiest way to do it, or if it exists.

I want to regulate a whole crap load in inputs. They can be anywhere from 5v to car voltage or higher for safety sake. So let's figure 5v-15v.

I want logical output (5 volt). I was thinking basically a relay driver type IC (ULN2803 or similar). But are these going to work with the high level inputs required? I was looking at the data sheet, and it looks like it won't.

So, what are my options? I know I could use voltage regulators, but I am hoping to get at least 8 inputs inline.

Any options, opinions, comments, flames?

greenman100 · 11-09-2005, 09:48 PM

you're not going to get much current without individual regulators/mosfets

kiltjim · 11-09-2005, 09:51 PM

It doesn't need much current. Its just for on/off sensing. A few milliamps would be more than enough. But very good point.

mushin · 11-09-2005, 11:11 PM

You don't think the ULN2803 would work? Both STMicro and Toshiba I looked up quick on digikey take input voltages up to 30V. I'm not an EE either, but that seems a viable route to me. Actually, I'm using a bunch of the STMicro ULM2803As for a project, I can test it out if you'd like.

Quote: Originally Posted by greenman100

you're not going to get much current without individual regulators/mosfets

I guess it doesn't matter in this case, but the ULN2803, for example, can do 500ma. That's a pretty decent current.

edit: I'm assuming you have a 5V source available? Because using a transistor array wouldn't be so much regulating the input current as switching a regulated current on with the unregulated input. I think that's what you're talking about but then occured to me maybe not.

kiltjim · 11-10-2005, 09:13 AM

Ok, I tested it, really quick and dirty like, and it works. I was using something like 9v on the input ( I don't have a bench supply right here...) and it lit the LED. Now, if it hadn't taken me 10 or so tries to get the thing working, I would have more confidence.

(So that's how the LED goes in.... Black is ground?!?... And what is this wire here? Do I even need it? Righty tighty, lefty loosey...)

HoSS · 11-11-2005, 06:36 AM

I think i understand (you question is a little confusing because u mention regulating) you want to take variable voltage inputs & pass them in as logic levels (on/off) right?
you can do it way simpler than that.
Use a resistor and a zener diode

R
Voltage ---[ ]---.----- Input
|
_
^
|
GND

where R value limits current to zener.
sorry for bad drawing.
If you want to be really safe add an optoisolator after.

kiltjim · 11-11-2005, 07:57 AM

That would work, and I don't believe I didn't think of that before. But, I think I am going to run with the relay driver. This way, if I want to run that port as a output instead all I need to do is change the setup slightly, and switch the chip around. In the end, it will only be a matter of logistics.

Thanks for all the help guys. Any more suggestions would be appreciated though!