Dngrsone

Hi guys. Been a while, I know.

I'm building a test-box for a small switch panel that runs on 28vdc and I want to AND two to four inputs so that the output is source voltage (the aforementioned 28vdc) to drive a lamp.

Were this device powered by 5vdc, I'd already have the tester together, using a couple quad-AND IC chips.

I wanted to do this with diode logic for simplicity's sake, but ran into a roadblock for two reasons-- up to now I have been using negative logic, and I don't want to create too much of a current draw during the "off" phase.

I thought maybe a couple diodes coupled with a FET might do the trick, but frankly, it's been something like twenty years since I did any kind of engineering with a transistor and I'm feeling a little overwhelmed by it.

Can anyone help me?

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Papabravo

The following family of so called peripheral drivers may be of interest to you. They can withstand high voltages at the output. If the sense is wrong then you can certainly use them to drive a PNP high side switch. In either case these are handy little goodies. We used to use them for hammer drivers on line printers. You remember line printers -- right?

http://focus.ti.com/lit/ds/symlink/sn75452b.pdf

Dngrsone

Thanks, this looks like it might do the trick. As I recall, max load should be less than 300ma. I'll try to find a couple and breadboard a sample circuit next week.

Oh, yes, I do remember line printers... still useful when coding-- ribbons last forever and print quality is not an issue when printing out code for editing.

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Leftyretro

Dam do I remember hammer drivers. I was working field service on mini-computer systems in the 70s. I remember having to do preventive maintenance procedures on drum line printers. 132 hammers and you had to move your second scope probe to each hammer circuit one at a time while you adjusted the mechanical stop adjustment such that the counter EMF pulse would line up with the column one hammer hooked to the first scope channel. What a laborious boring task that was, took hours sometimes but if you didn't do it every 6 months or so the customer would notice the the print lines were wavy

Back in those days a high speed drum printer or a dual removable hard-disk drive would cost as much or more then a normal 3 bedroom home Heck the ten high platter blank removable disks cost more the $1,000

Lefty

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Pommie

Assuming that the inputs will be 0 or 28V then something like this should work.

Mike.
Edit, just realised that's a NAND gate. Another stage would fix that.

Attached Images

AND gate.GIF (2.3 KB, 21 views)

Dngrsone

Actually, that would work nicely as I am using negative logic (I need all LOs to get a LO). Thanks, much!

Lefty-- I was so glad I didn't have to deal with those 10-packs. I used work on HP 7906 dual drives (one fixed, one removable; 18" platters). Those things crashed on an almost weekly basis and aligning the replacement fixed platter would test anyone's patience.

Once I got people to stop smoking in the lab, things quieted down a bit-- those micron filters worked only so much.

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Pommie

Unfortunately, NAND = all hi = lo out.

If you switch the diodes around and swap the pnp for npn and reverse the power supply, then you will get all lo = light out, an OR gate. Another transistor stage will give you what you need.

Mike.

on1aag

Hi Dngrsone,

Try this.

on1aag.

Attached Images

NAND.GIF (8.4 KB, 25 views)

grim

4 relays, with their contacts in series?

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