Clyd3

Hi everyone.
Got a dental handpiece here which needs a transformer for its light.
It's a 3.5V little bulb.
I'm just deciding the best way to go about putting together power for the little guy.

I know I could get 3.6V from a pc power supply, but that's large and chunky - I'd like the place to be neat and organized (which it isn't). I wouldn't mind using one of those wall warts (because that's in the socket (still smallish) and regulating from there.

Googling for a while (these are my options so far) - if I don't give in to using a pc power supply, to use a zener diode (3.6v) or a lm317.
The advantages of using a lm317 in power supplies from what I understand is that they have current limiting and overheating protection. But they seem to normally be used for regulated power supplies. Would one be suitable for this fixed voltage?

I don't know how to use zener diodes yet (wouldn't take too much to learn) and i know you get 3.6v zeners. Would this be a better option?

In summary I want a nice small setup which won't kill the bulb - any pointers or amazing hints?
My main concern is: Very little is known about this expensive little lightbulb other than it is 3.5V. What are the risks of burning it out with too much current or something? and how can I reduce the chance of damaging the bulb?

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mneary

Use a 3V wall transformer such as All Electronics DCTX-31

Ubergeek63

it sounds like you have a dental blue LED, the UVs cost even more.

DO NOT USE A WALL WART ALONE!!!

The LED *REQUIRES* a current source, you MUST use a special supply to drive it. While the wall wart will supply the power it will not regulate the current, you need to get an LED driver of some sort.

Expensive? I'll say! The UVs I believe go for $150 each in qty. Our customer blew a few early on since they did not give us sufficient info to design the driver.

LED-100 UV Portable Spot System - Detail information for LED-100 UV Portable Spot System

This thing runs for a couple hours on it's internal lithium cell.

Clyd3

no it's definitely not an led. It looks like a xenon bulb.

Do you think i still need to worry lots about limiting the current to this thing?

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davidbball13

you could get a 3.6volt coin cell. jk

picbits

Use a 6 to 7.5 volt unregulated wall wart with a LM317 adjusted to 3.5 volts.

Job done

audioguru

No.
If the light is an LED then it will be destroyed, it will light or it will not light.
An LED needs to have its current limited to below its max rating. You can use an LM317 as a current regulator (not a voltage regulator) if you want.

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ronsimpson

“Dental hand piece”? Are you using this on people?
“Wall warts” are not medical grade power supplies.
If you are going to use this on people we need to talk about government regulations!
If you are using the light in a non-medical application then wall warts are OK.

picbits

Before I posted that I noticed he said it wasn't an LED, it looked like a xenon bulb. If this is the case then he can use the LM317

If it is a specialist LED then obviously your above comments are true.

Clyd3

Sorry I didn't reply sooner - hectic yesterday (my birthday and everything)
Thanks for all the help and advice!

Had another good look at the light - it's definitely not an led. Gonna use the 317 and wall wart.

Yes I'm using it on people - of course... I'm in africa after all... (jokes)
My dad's a jeweller. He has a dental tech friend who showed him his equipment including dental handpieces which are entirely superior to the tools the jewellers use and as with all medical equipment, rediculously expensive. So we ebay'd one here and just want to set it up a light. My advice to anyone who uses handpieces, especially with more delicate work. Do the same. It's really worth it...

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ericgibbs

hi Clyd,
I had a friend who's father was dentist, he gave me allsorts of gizzmo's

Ideal for hooking out ic's, tracing wire in looms and gripping components.

Where in SA are you.?

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Eric
"Good enough is Perfect"

PIC tutorials:
Gramo's: www.digital-diy.net/
Bill's: www.blueroomelectronics.com/

Clyd3

It is really useful stuff isn't it. Knowledge is really power when it comes to equipment.
I'm in Durban, why?

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shokjok

You can use a 78L05 voltage regulator with 2 forward-biased 1N914 diodes on its ground pin to reduce the output voltage to 3.6V, powered by coin cells ( aka disc batteries) or rechargeable N batteries ( half-size AA ) in the handle.

Nigel Goodwin

You are confused, diodes in the ground pin INCREASE the voltage, not decrease it.

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Hero999

The diodes need to be in series with the output of the regulator.

Using diodes is a bad idea because it totally ruins the voltage regulation.

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