AC / DC Converter IC

[Szewczykm]

Maybe this should be in the beginners forum, I'm not sure.  I'm building a test fixture for pinball bulbs for a friend of mine.  Pinball machines will use AC or DC power for light bulbs and he wants to be able to flip back and forth between AC and DC.

I figured it wasn't a problem and thought that I would use a 6v AC wall wart for power.  Then I'd use a DPDT switch to flip between AC and DC.  One side would go straight through, and the other side would go through a circuit to convert the output to DC.

I hadn't done all of the figuring yet but I thought that to get the DC I would go through a full wave bridge rectifier with a smoothing cap and then maybe use a voltage regulator or just a zener to keep the voltage at 6v.  I know there would be some voltage loss.  I figured I'd work on it and figure out how to get consistent 6v DC / 6v AC.

I thought that I'm not the first guy to do this and maybe there's a package that does all of this already in a single component.  Is there a AC/DC converter IC that people use for this kind of thing?

Also, what might I be bumping my head on that's obvious but not so obvious to someone who has lived in DC land for the past couple of years?

Thanks!

Mike

[TerminalJack505]

I can't think of a ready-made solution but your idea of just using a wall wart and some components sounds fine to me. 

I don't think I would bother with a regulator.  Especially for something like a bulb.  If you use a 6VAC transformer, rectify it and use a big enough capacitor then you'll get close to 6VDC across a load like a bulb.  The key is to use a really big capacitor.  You might get a little more than 6VDC, in which case you can use one or more diodes to drop the voltage.

If you do use a regulator you will still need a really big capacitor and a low dropout regulator because you won't have much headroom between the rectified voltage and a 6VDC output.

[Paul Price]

Why in world would you need to switch between AC and DC to test incandescent light bulbs? Either AC or DC would work the same to see if the bulb is ok.

[c4757p]

AC or DC power for light bulbs and he wants to be able to flip back and forth between AC and DC.

Oh, brother. Does he also want to switch between 50, 60 and 400 Hz? Sine, square and triangle? Amplitude modulation?

[free_electron]

AC or DC power for light bulbs and he wants to be able to flip back and forth between AC and DC.

Oh, brother. Does he also want to switch between 50, 60 and 400 Hz? Sine, square and triangle? Amplitude modulation?

well ,  a lot of these light bulbs are actually time multiplexed ..... so we need variable duty pwm signals driving em .....

[TerminalJack505]

I think some of the new 'bulbs' used in pinball machines are really just LEDs but in a bulb-like package.

[Szewczykm]

Yea, sometimes when asking questions I feel it necessary to leave some things out.  The bulbs that are being tested are actually led bulbs.  Some bulbs have polarity, others have rectifiers built in.  "Why" isn't terribly important to the question.  I was just curious to know if there was an IC that does a good job of making ac, dc in a single package.

[TerminalJack505]

They do make bridge rectifiers in a single package.  It's basically just the 4 diodes you'd otherwise have in a single package.

You can get 80% of what you need for this project from a 6VDC wall wart.  If you take a hacksaw to one and open it up you will find the transformer, 4 rectifier diodes and a capacitor.  (Personally, I'd throw the capacitor away, however, and use a name brand.)

[Crazy Ape]

They do make bridge rectifiers in a single package.  It's basically just the 4 diodes you'd otherwise have in a single package.

You can get 80% of what you need for this project from a 6VDC wall wart.  If you take a hacksaw to one and open it up you will find the transformer, 4 rectifier diodes and a capacitor.  (Personally, I'd throw the capacitor away, however, and use a name brand.)

Quite a few new ones are switch-mode supplies so this could be an issue.

[Rigby]

[ pictures ]

What did you use to simulate that?  I'm not familiar with that software.

[TerminalJack505]

[ pictures ]

What did you use to simulate that?  I'm not familiar with that software.

That's the Tina-TI simulator.  TI licenses a chopped-down version of the commercial Tina product from a company called DesignSoft.  It does most of way I ever need to do.  Sometimes it won't have a component I need but I can usually find and import a Spice version and it will work.

[tszaboo]

Yes, with a full wave rectifier, you are losing 1.6-2V from a sqrt(2)*6V=8,48V rectified DC voltage, depending on the current. And your voltage regulator (again, depending on your current and type) will not be happy with only 0.48 drop voltage. What you could use, is an active rectifier. It uses MOSFETS instead of diodes, so the voltage drop is much less. I wrote an article some weeks back about this, it is a single chip 4 mosfet solution. Depending on your soldering skills, you  could put this together, and make it work.
http://nandblog.com/chip-review-ltc4320/

[TerminalJack505]

That's a pretty interesting IC.  Schottky diodes might work for this application as well if the OP really wants to regulate the DC voltage.