Xenon flash capacitor charging

[CaleJo]

I am trying to modify a disposable camera flash unit to be powered by a DC power supply instead of a battery. I am trying to use a 12V power supply and regulate it to 1.5V.

The problem I am having is that the capacitor won't charge using this method. I have tried a simple voltage divider as well as a voltage regulator. Is there anyone who could lend some insight?

My first thought was that the new power circuit stabilized the oscillation in the original circuit, but I am not sure.

 

[alehman]

What is the ampere capacity of you power supply & regulator? You may need several amps.

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[itsmoked]

The camera flash was powered only with 1.5V? Usually they are at least 3V.

In the first sentence you seem to be asking about voltage regulation...

In your second sentence, you are talking about capacitor charging? What capacitor specifically?

Have you tried a 1.5V battery again? One brief screw-up and no voltage will work anymore.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[CaleJo]

alehman: I think you are right about the amperage. I don't think I used a regulator that could provide enough current.

itsmoked: This particular flash unit is powered by 1.5V. The battery works fine but my application requires the use of a power supply (the battery would run out way to fast). The capacitor is a 120uF 300V cap. I need to charge it to 300V which is where I am running into problems. If you have any ideas on how to do this, I am all ears. I would rather design a flash unit from scratch to meet my needs, rather than hack an existing circuit.

Are there any other approaches to this problem other than using a fly-back transformer to charge the cap? Could another type of oscillator circuit do the job.

 

[itsmoked]

There are several capacitor charge controllers for flash units.

Here's an example:

http://cds.linear.com/docs/Datasheet/3751fa.pdf

Keith Cress
kcress -

http://www.flaminsystems.com

 

[alehman]

Or if you want to take it "old school" and build from scratch -

http://www.talkingelectronics.com.au/projects/XenonFlasher/XenonFlasher.html

Alan
----
"It’s always fun to do the impossible." - Walt Disney

 

[CaleJo]

itsmoked: Thanks for the link. I have actually checked into this solution, but can't find a super small 1:10 flyback transformer to use with it. The only supplier I found would only sell me 500 units at a time. I need to build 5 units only so this is not an option. The transformers in the disposable cameras have a turns ratio of 1:350 and won't work with the IC you linked me to.

alehman: Thanks, I have actually been to this site and found some good info. There is also a ton of info here

http://repairfaq.cis.upenn.edu/sam/strbfil.htm

I think I am stuck hacking an existing flash unless I can find a small 1:10 flyback transformer. Another catch is that the transformer has to have a frequency response around 10 KHz (this is the hum you hear when you charge a flash).

 

[itsmoked]

Well there's also just buying a HV converter:

http://www.picoelectronics.com/dcdc_hp/HiVoltage.htm

Or they sell miniature transformers:

http://www.picoelectronics.com/index.htm

Everyone seems to be going to HBLED flash in small designs.
National has many solutions there:

http://www.national.com/JS/searchDocument.do?textfield=flash+capacitor&x=42&y=12

National may even have demo boards.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[CaleJo]

I hadn't thought of just using a DC-DC converter. I will be looking into this further. Thanks.

As for the LED flash. I currently am using high power LED's (always on) for lighting and they aren't bright enough so I am trying the xenon flash.

Are the LED flashes brighter/different than a high power LED that is always on?

 

[itsmoked]

Depends..

LEDs can take high currents but nothing changes in the average current picture. So you can goose them harder with an appropriate duty cycle that keeps their average current low.

It's all over the map on how much overdrive you can apply to any particular LED.

Are you using HBLEDs now that aren't bright enough? Some of them are insanely bright. You can also get all sorts of snap-on optics to profile the light into a beam.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[CaleJo]

Yes I am using a HBLED. Part of the problem is my particular application. I have to use a small aperture lens to avoid depth of field problems. I am testing a Xenon in hopes it will flood my scene far greater than the HBLED I was using. I guess I will see.

I have looked into the optics and I need a very diffuse light source so concentrating the light into a beam wouldn't work in this case. I am using the HBLED as a back light.

Thanks for all the tips. They definitely help and are appreciated.

All that said, I am going to move forward with the xenon flash idea. If that fails, I will look into LED flashes and see if there is something brighter than what I am using presently.

Also, I was able to get the flash unit to charge using a more powerful voltage regulator.