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Trigger a disposable Flash

T

Terry

Jan 1, 1970
0
I am looking for a very simple circuit for shorting the trigger wires from a
disposable flash from my parallel port. I do this all the time with diodes,
etc for my DC circuits - but with this I need to isolate the 300 - 400v of
AC that is on the trigger wires. (I have the flash trigger itself all built,
I just have to short the trigger wires - and poof!)

Is there a simple optoisolator circuit out there or will I also have to add
a SCR or Triac?

Thanks!
 
N

Norm Dresner

Jan 1, 1970
0
Terry said:
I am looking for a very simple circuit for shorting the trigger wires from a
disposable flash from my parallel port. I do this all the time with diodes,
etc for my DC circuits - but with this I need to isolate the 300 - 400v of
AC that is on the trigger wires. (I have the flash trigger itself all built,
I just have to short the trigger wires - and poof!)

Is there a simple optoisolator circuit out there or will I also have to add
a SCR or Triac?

I don't know what your current requirements are, but there are plenty of
optoisolators with triacs (and IIRC SCRs) available to choose from

Norm
 
T

Terry

Jan 1, 1970
0
I am guessing the current is very small, but I am not sure at this point. I
am just experimenting at this point. I am not very familiar with Triacs so
a little help would be appreciated.

I was looking at using a MOC3052 - one end to the PC and the other directly
to the trigger. Does this sound reasonable for this application? I think
the triac can sink 1A, I know it would not exceeded that.
 
H

Howard Henry Schlunder

Jan 1, 1970
0
The typical disposable flash trigger circuit contains a 22nF capacitor
charged to 330V and it gets discharged through a low impedance pulse
transformer primary through a mechanical switch. Although it is true that
average trigger current is way less than 1A no matter how fast you trigger
the xenon strobe, the peak pulse current exceeds 100A, possibly even 200A.
As such, you may wish to use an SCR or TRIAC which is rated for this type of
operation, such as the MCR22-6 [
http://www.onsemi.com/pub/Collateral/MCR22-6-D.PDF ] (assuming you can find
a supplier). Although I've never used a MOC3052, I would hazard a guess
that it would be only useful for triggering a larger SCR or TRIAC and would
explode on the very first trigger if used by itself.

Howard Henry Schlunder

in message
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W

Watson A.Name - Watt Sun

Jan 1, 1970
0
I am looking for a very simple circuit for shorting the trigger wires from a
disposable flash from my parallel port. I do this all the time with diodes,
etc for my DC circuits - but with this I need to isolate the 300 - 400v of
AC that is on the trigger wires. (I have the flash trigger itself all built,
I just have to short the trigger wires - and poof!)

Is there a simple optoisolator circuit out there or will I also have to add
a SCR or Triac?

Thanks!

I would use a reed relay, maybe a 6V or 5V one. If you're worried
about the high current needed for the coil, well, reed relays don't
take that much current, only a few dozen mA, or less. But you can put
a couple hundred uF cap in series with the coil, with a few k bleeder
resistor across the cap. When you charge the cap thru the coil, it
will pull the contacts in momentarily, long enough to trigger the
flash. Then the coil current will go down to only a mA or so.


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G

GrahamH

Jan 1, 1970
0
Watson A.Name - Watt Sun said:
I would use a reed relay, maybe a 6V or 5V one. If you're worried
about the high current needed for the coil, well, reed relays don't
take that much current, only a few dozen mA, or less. But you can put
a couple hundred uF cap in series with the coil, with a few k bleeder
resistor across the cap. When you charge the cap thru the coil, it
will pull the contacts in momentarily, long enough to trigger the
flash. Then the coil current will go down to only a mA or so.
Have a look at AQV251 photomos, stock code 171-8623 at www.rswww.com. Micro
current opto switch. Just add one series resitor to limit LED current. I
have also used these to switch from the handshake lines of a PC serial port.

Graham
 
W

Watson A.Name - Watt Sun

Jan 1, 1970
0
The typical disposable flash trigger circuit contains a 22nF capacitor
charged to 330V and it gets discharged through a low impedance pulse
transformer primary through a mechanical switch. Although it is true that
average trigger current is way less than 1A no matter how fast you trigger
the xenon strobe, the peak pulse current exceeds 100A, possibly even 200A.
As such, you may wish to use an SCR or TRIAC which is rated for this type of
operation, such as the MCR22-6 [
http://www.onsemi.com/pub/Collateral/MCR22-6-D.PDF ] (assuming you can find
a supplier). Although I've never used a MOC3052, I would hazard a guess
that it would be only useful for triggering a larger SCR or TRIAC and would
explode on the very first trigger if used by itself.

Howard Henry Schlunder

I suggested using a reed relay to trigger it. I didn't think that the
peak curent would be that high, but it makes sense, it's a CD, a
capacitive discharge system. I guess a reed relay wouldn't explode,
but after the contacts fused, the experimenter would get the hint and
use something a bit heavier. :p

One thing I didn't notice on the contacts on the displosible flash I
have is any pitting or arcing of the pushbutton contacts. But then
they're a lot heavier than a reed relay.
in message

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@@F@r@o@m@@O@r@a@n@g@e@@C@o@u@n@t@y@,@@C@a@l@,@@w@h@e@r@e@@
###Got a Question about ELECTRONICS? Check HERE First:###
http://users.pandora.be/educypedia/electronics/databank.htm
My email address is whitelisted. *All* email sent to it
goes directly to the trash unless you add NOSPAM in the
Subject: line with other stuff. alondra101 <at> hotmail.com
Don't be ripped off by the big book dealers. Go to the URL
that will give you a choice and save you money(up to half).
http://www.everybookstore.com You'll be glad you did!
Just when you thought you had all this figured out, the gov't
changed it: http://physics.nist.gov/cuu/Units/binary.html
@@t@h@e@@a@f@f@l@u@e@n@t@@m@e@e@t@@t@h@e@@E@f@f@l@u@e@n@t@@
 
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