DIY studio strobe
in [Design]
|
From: Jim Thompson on 30 Jan 2010 11:08 On Sat, 30 Jan 2010 09:19:59 +0100, "Ban" <bansuri(a)web.de> wrote: > >"El Loco Mateo" <ellocomateo(a)free.fr> schrieb im Newsbeitrag >news:4b636ad8$0$5384$426a34cc(a)news.free.fr... >> On 2010-01-29 15:19, MooseFET wrote: >>> If you know about MOSFETs and bipolar transistors, you and think of an >>> IGBT as an N channel MOSFET feeding a PNP transistor. >>> >>> You need to apply a pulse to the gate of the IGBT that is about 10V >>> tall and lasts for as long as you want the current to flow. The gate >>> of the IGBT must be moved from near zero to the near 10V and back >>> quickly. Holding it high and low is the easy part. >>> >>> The IGBT must be in the path of the current through the tube. You >>> can't control the tube via the trigger electrode once it is fired. >>> The plasma inside the tube is a short circuit. You need to open one >>> end connection of the tube by turning off the IGBT in that path. >> >> Thank you both for your comments! Is an IGBT the only solution to achieve >> my goal? What other alternative do I have, should I want to reach currents >> higher than say 150A? > >Wouldn't it be easier to fire an SCR in parallel to the tube to eat up the >remaining charge? No floating grounds, can use the normal ignition >transformer. >ciao Ban >Apricale, Italy > See... Patent 3,496,411, "Timing Circuit for a Flash Camera" on my website. ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | I love to cook with wine. Sometimes I even put it in the food.
From: MooseFET on 30 Jan 2010 11:15 On Jan 29, 11:11 pm, "Tim Williams" <tmoran...(a)charter.net> wrote: [... photoflash ...] > > What else is there to reflect on... BJTs? Imagine the darlington you'd need > to switch a flash tube. ;-) To reduce losses, you wouldn't want a darlington's extra drop. I am thinking of something more like this: +3V ------------+------- ! ! !/ e Q1 ! logic -/\/\---! PNP ! !\ c !Q2 ! !/ Q3 +-----!NPN ----+-------+-Tube ! !\e !/ ! ! \ +--/\/\-! === C1 [R] High voltage / ! !\e ! ! resistor \ \ ---+-------+-GND ! / GND \ ! GND If Q3 needs to pass 150A and has a HFE well above 30, Q2 only needs to take perhaps 5A from the +3V rail. Q1 would only need to pass perhaps 100mA. This puts the Base drive of Q1 well within the range of 5V 74HCxx logic. C1 keeps the voltage on Q3 from rising until the base charge has been removed. The high voltage resistor discharges C1 between shots. > > Tim > > -- > Deep Friar: a very philosophical monk. > Website:http://webpages.charter.net/dawill/tmoranwms
From: MooseFET on 30 Jan 2010 11:20 On Jan 30, 12:19 am, "Ban" <bans...(a)web.de> wrote: > "El Loco Mateo" <ellocoma...(a)free.fr> schrieb im Newsbeitragnews:4b636ad8$0$5384$426a34cc(a)news.free.fr... > > > > > On 2010-01-29 15:19, MooseFET wrote: > >> If you know about MOSFETs and bipolar transistors, you and think of an > >> IGBT as an N channel MOSFET feeding a PNP transistor. > > >> You need to apply a pulse to the gate of the IGBT that is about 10V > >> tall and lasts for as long as you want the current to flow. The gate > >> of the IGBT must be moved from near zero to the near 10V and back > >> quickly. Holding it high and low is the easy part. > > >> The IGBT must be in the path of the current through the tube. You > >> can't control the tube via the trigger electrode once it is fired. > >> The plasma inside the tube is a short circuit. You need to open one > >> end connection of the tube by turning off the IGBT in that path. > > > Thank you both for your comments! Is an IGBT the only solution to achieve > > my goal? What other alternative do I have, should I want to reach currents > > higher than say 150A? > > Wouldn't it be easier to fire an SCR in parallel to the tube to eat up the > remaining charge? No floating grounds, can use the normal ignition > transformer. You need to put a resistor in series with that SCR. Resistors rated for that sort of duty can be a bit hard to come by. The power in that pulse can be very high even though it is very short. For a home project, I would most likely make my own resistor out of copper wire. Copper is soft and thermally conductive enough that the heat pulse doesn't cause a lot of stress. > ciao Ban > Apricale, Italy
From: Jan Panteltje on 30 Jan 2010 11:38 On a sunny day (Sat, 30 Jan 2010 08:20:47 -0800 (PST)) it happened MooseFET <kensmith(a)rahul.net> wrote in <19297e0a-f274-4a97-ba88-080859c431ec(a)w27g2000pre.googlegroups.com>: >You need to put a resistor in series with that SCR. Resistors rated >for that >sort of duty can be a bit hard to come by. The power in that pulse >can be very >high even though it is very short. For a home project, I would most >likely >make my own resistor out of copper wire. Copper is soft and thermally >conductive 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... HV charge current >--------- L1 ------------------------------- | | | | { } Flash bulb | === | | --- C1 | / early discharge switch. | / fire switch | | | | GND -----------------------------------------------------------
From: whit3rd on 30 Jan 2010 13:50
On Jan 30, 12:19 am, "Ban" <bans...(a)web.de> wrote: [about turning OFF a discharge lamp ] > >> The IGBT must be in the path of the current through the tube. > Wouldn't it be easier to fire an SCR in parallel to the tube to eat up the > remaining charge? Exactly correct. If you put a small choke in series with the tube, the SCR needn't conduct high currents for long, either, to quench the arc while leaving the power supply full of electrons. SCRs, however, have a dI/dt limit (they can't fire quickly) so you don't want to use inexpensive phase-control devices for this. OptoSCRs have the best dI/dt performance. The series switch idea, while good, has risetime limits (if you want one microsecond control, the turnoff will put hundreds of V/us on the switch). Miller effect makes this a problem. |