Hi to all.

I have some simple circuit from disposable camera.
It is for flash control.

http://img824.imageshack.us/img824/4456/77158871.jpg

I want to control of time of discharge of that big 300 uF capacitor. If the time for full discharge is T, I want to have times like T/2, T/30 or even T/100

I read somewhere that it should be made with thyristor, but have not find any solution.

Regards

 

Hello,

What will be the application?

Keep in mind that the high voltage on the capacitor can b leathal.

Bertus

 

The application is using this for catching some very fast speed photos.

As I know, original flash setting of disposable camera has speed (capacitor discharge) of 1/1000 second.

I need to have control, to cut time on half 1/2 r even 1/100 of this original, so I will have flash which will last for about 1/100000 of second.

 

Simplest way would be to replace the capacitor with a smaller high voltage one. For example a 4.7 to 22µF/400V mains filter capacitor can be found in many cheap electronic appliances. Be very careful to ensure the capacitor is discharged before removing it.

 

and how to have multi capacitor, with diferent capacity, so I can pick what I need just before shot ?

 

Time for full discharge is infinity. Think instead about discharge by some fraction 1/e is a common one. Timing is RC, I think it is easiest to change R. For timing no need to start with 300 v. 10 v should be fine.

 

Time for full discharge is infinity. Think instead about discharge by some fraction 1/e is a common one. Timing is RC, I think it is easiest to change R. For timing no need to start with 300 v. 10 v should be fine.

I cannot understand your last sentence.

For timing no need to start with 300 v. 10 v should be fine

But for that info about changing R, can you tell me what values I should choose. 2-3 Mohm ? or smaler 0.1 Mohm ?

 

The application is using this for catching some very fast speed photos.

As I know, original flash setting of disposable camera has speed (capacitor discharge) of 1/1000 second.

I need to have control, to cut time on half 1/2 r even 1/100 of this original, so I will have flash which will last for about 1/100000 of second.

Hi zsbreaker!
I could'nt find the diagram on your link. By the way fast photography is linked with shutter speed not the flash. Plz explain?

 

Hi zsbreaker!
I could'nt find the diagram on your link. By the way fast photography is linked with shutter speed not the flash. Plz explain?

I did a little searching and found a commercially available flash with 9usec width. You won't get that with a mechanical shutter.

 

I cannot understand your last sentence.

For timing no need to start with 300 v. 10 v should be fine

But for that info about changing R, can you tell me what values I should choose. 2-3 Mohm ? or smaler 0.1 Mohm ?

I don't think Russ is on the same page as you are. I doubt that 10V is enough to light up a Xenon flash tube.

 

I don't think Russ is on the same page as you are. I doubt that 10V is enough to light up a Xenon flash tube.

I was just reacting to the desire to determine the timing, not the lighting of the tube. If what he wants to do is quench the flash, then you do not use RC timing, but either open the circuit, or short the cap to drive the voltage to 0.