Modern flash units do cut down the duration of the flash if not the entire charge on the capacitor is needed, this preserves the remainder of the stored energy in the capacitor and makes the flash duration shorter. Always be careful building a strobe like unit and comparing it to camera flash units as it is important to realize the bulb limits have to do with both the peak energy in one flash and the total energy over time. (cooling issues). If you wish to raise the amount of energy at the same flash rate you also may have to change the charge circuit. Peter van Hoof ----- Original Message ---- > From: Alan B. Pearce > To: Microcontroller discussion list - Public. > Sent: Monday, July 20, 2009 4:21:29 AM > Subject: Re: [EE] High voltage opto-coupler > > >There certainly are some intricacies to protect the tube and capacitor > > Normal photographic flashes extend the life of the tube by limiting the rise > time of the current by using specific lengths of wire between the capacitor > and the tube, thereby providing a suitable series inductance that limits > di/dt. Early model flashguns that used paper dielectric capacitors charged > to around 2kV could produce an extremely short and intense flash. > > I have spoken to commercial photographers who used these old units and > considered it normal to be able to get an extremely sharp stop motion of a > ballet dancer doing a twirl, and in the photo the outer edge of the skirt is > absolutely crisp sharp in the photo. > > later units that used electrolytic capacitors charged to around 500V do not > have the same short flash, as the internal impedance of the capacitor lowers > the di/dt. Also I suspect the lower operating voltage means the tube is > harder to fire. > > The most modern units seem to run at around 200-300V across the storage > capacitor. > > -- > http://www.piclist.com PIC/SX FAQ & list archive > View/change your membership options at > http://mailman.mit.edu/mailman/listinfo/piclist -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist