DIY studio strobe
in [Design]
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From: Tim Williams on 30 Jan 2010 15:19 "Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message news:hk1n9k$puc$1(a)news.albasani.net... > I think the normal procedure is to have a small inductor in series with > the flash bulb, > to lengthen the flash, the lifetime of the capacitor, and to reduce the > maximum current... Last time I saw one was on some old Kodak flash. From one of those cameras with the flat type battery pack! On the other hand, my ex-Canon S1 IS: http://webpages.charter.net/dawill/Images/CameraBits.jpg contained an awfully small 220uF 330V electrolytic, attached with impressively thin wires (which I'm guessing are slightly thicker than the film PCB stuff they use for all other connections). On the board are an inverter (or trigger?) transformer, some transistors, capacitors, a diode, and an incredibly small IGBT -- smaller than SO-8, I forget what part number but it's rated at 150A peak, 400V or so, and 4Vce(sat) at 150A -- pulsed, obviously. Ic continuous is like 10A. No inductors or resistors between the flash and capacitor. A cap that size is more than resistive enough to require no additional help. This approach definitely turns off the flashtube: after sitting a while, the camera has to recharge the cap before you can take a flash photograph. Once it's charged, you can take lots of flashes with little delay. And that's while it does its double flash thing. Pretty neat. Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Tim Williams on 30 Jan 2010 15:11 "MooseFET" <kensmith(a)rahul.net> wrote in message news:bc025161-f7b4-429d-9d5e-39e2a43c02bb(a)l12g2000prg.googlegroups.com... > To reduce losses, you wouldn't want a darlington's extra drop. I am > thinking of something more like this: > > <snip> > > If Q3 needs to pass 150A and has a HFE well above 30, Q2 only needs to > take perhaps 5A from the +3V rail. Ah, but how many transistors have you seen with hFE > 30 that do 150A peak *and* over 400V? Possibly some ISOTOP modules would actually work... it would be quite amusing to see a camera where the flash module is bigger (and more expensive!) than the lens assembly! :-) The annoying part about BJTs, you can't pulse them much beyond ratings, where hFE goes to zero and Vce(sat) explodes. So you'll end up needing like 150A of base current to make it work, which makes a GTO look a lot better... you still need 150A, but it's only a short pulse. Even getting 5A from inside a camera would be fairly impressive, let alone 150A, but I suppose that, like the flash itself, it would all be pulsed from some other big cap. Maybe an overrated boost/buck/SEPIC to keep it around 3V while the cap gets sucked out, before the battery can keep it going. > C1 keeps the voltage on Q3 from rising until the base charge has been > removed. The high voltage resistor discharges C1 between shots. Mmmm, snubbing a 150A BJT, inside a camera... that thing will be bigger than the photoflash cap itself! Tim -- Deep Friar: a very philosophical monk. Website: http://webpages.charter.net/dawill/tmoranwms
From: Jan Panteltje on 30 Jan 2010 18:03 On a sunny day (Sat, 30 Jan 2010 14:19:01 -0600) it happened "Tim Williams" <tmoranwms(a)charter.net> wrote in <hk247p$qn1$1(a)news.eternal-september.org>: >"Jan Panteltje" <pNaonStpealmtje(a)yahoo.com> wrote in message >news:hk1n9k$puc$1(a)news.albasani.net... >> I think the normal procedure is to have a small inductor in series with >> the flash bulb, >> to lengthen the flash, the lifetime of the capacitor, and to reduce the >> maximum current... > >Last time I saw one was on some old Kodak flash. From one of those cameras >with the flat type battery pack! > >On the other hand, my ex-Canon S1 IS: >http://webpages.charter.net/dawill/Images/CameraBits.jpg >contained an awfully small 220uF 330V electrolytic, attached with >impressively thin wires (which I'm guessing are slightly thicker than the >film PCB stuff they use for all other connections). On the board are an >inverter (or trigger?) transformer, some transistors, capacitors, a diode, >and an incredibly small IGBT -- smaller than SO-8, I forget what part number >but it's rated at 150A peak, 400V or so, and 4Vce(sat) at 150A -- pulsed, >obviously. Ic continuous is like 10A. > >No inductors or resistors between the flash and capacitor. A cap that size >is more than resistive enough to require no additional help. > >This approach definitely turns off the flashtube: after sitting a while, the >camera has to recharge the cap before you can take a flash photograph. Once >it's charged, you can take lots of flashes with little delay. And that's >while it does its double flash thing. Pretty neat. > >Tim Do you put it back together :-)?? Maybe that cap is inductive too? may be worth measuring it, if it is a foil type electrolytic sometimes those become inductive if the foil does not make good contact over the edges... I would not dare to take my Canon apart, it is a far too nice camera. >-- >Deep Friar: a very philosophical monk. >Website: http://webpages.charter.net/dawill/tmoranwms > > >
From: MooseFET on 30 Jan 2010 19:33 On Jan 30, 12:11 pm, "Tim Williams" <tmoran...(a)charter.net> wrote: > "MooseFET" <kensm...(a)rahul.net> wrote in message > > news:bc025161-f7b4-429d-9d5e-39e2a43c02bb(a)l12g2000prg.googlegroups.com... > > > To reduce losses, you wouldn't want a darlington's extra drop. I am > > thinking of something more like this: > > > <snip> > > > If Q3 needs to pass 150A and has a HFE well above 30, Q2 only needs to > > take perhaps 5A from the +3V rail. > > Ah, but how many transistors have you seen with hFE > 30 that do 150A peak > *and* over 400V? Only 1 and I think that is enough. :) The "data book" had about 3 devices in it and had a tank on the cover. The name of the company was something like Powertek or powerteck IIRC the price tag had more digits in it than I cared to think about. > Possibly some ISOTOP modules would actually work... it > would be quite amusing to see a camera where the flash module is bigger (and > more expensive!) than the lens assembly! :-) I've already seen that. Doc Edgerton built it in WW-2. The flash had a refector about 3 feet across and the flash tube was about the size of a couple of human fists put together. The box that made it go was a couple of feet on a side. It was developed to take photos from the air at night. > > The annoying part about BJTs, you can't pulse them much beyond ratings, > where hFE goes to zero and Vce(sat) explodes. So you'll end up needing like > 150A of base current to make it work, which makes a GTO look a lot better.... > you still need 150A, but it's only a short pulse. GTOs don't like really fast di/dt. They don't spread the conduction state over the whole device unless there is some current flowing. It takes a while for the whole device to get turn on. > > Even getting 5A from inside a camera would be fairly impressive, let alone > 150A, but I suppose that, like the flash itself, it would all be pulsed from > some other big cap. Maybe an overrated boost/buck/SEPIC to keep it around > 3V while the cap gets sucked out, before the battery can keep it going. > > > C1 keeps the voltage on Q3 from rising until the base charge has been > > removed. The high voltage resistor discharges C1 between shots. > > Mmmm, snubbing a 150A BJT, inside a camera... that thing will be bigger than > the photoflash cap itself! I wasn't figuring on a 1206 NPO. > > Tim > > -- > Deep Friar: a very philosophical monk. > Website:http://webpages.charter.net/dawill/tmoranwms
From: MooseFET on 31 Jan 2010 12:59
On Jan 29, 2:30 am, El Loco Mateo <ellocoma...(a)free.fr> wrote: > Hello, > > I would like to build my own studio strobe, based on the following > design [I am well aware about the risks of high voltage/current!]: > > http://www.diyphotography.net/diy-home-made-power-pack-flashes#great-... > > The only thing I would like to further implement is a control on the > flash duration/power. To my understanding, one has to replace the SCR > with an IGBT, in the triggering circuit. Could some one please confirm > this point? > > Unfortunately IGBTs are new to me and I would really appreciate some > hints/tutorial on how to replace the SCR based trigger with an IGBT > based circuit? > > Could someone here help me improve my knowledge please? > > Best regards, I just thought of another interesting way to do it: The idea of using a second SCR to short the terminals of the tube is good except that it requires the the SCR take a huge current spike to discharge the storage capacitor. Another device that can take a big current spike is another tube. ----/\/\--------------- ! ---+-------+-----!!-----+- ! ! ! === [Tube1] [Tube2] ! ! ! ---+-------+-------------- Tube1 is the working tube. Tube2 is a second tube that is hidden. The capacitor feeding Tube2 is so that Tube2 will have a slightly higher voltage on it than Tube1. This voltage difference is equal to the struck voltage of Tube2. When Tube2 fires it forces the voltage on Tube1 to near zero. |