Simulate a Digital camera's Pre Flash? - Electronic Circuits Projects Diagrams Free

1Steveo · 7th February 2005, 03:04 AM

I need to have a Camera's Strobe Flash 2 rapid times aprox. 400 mill seconds apart. Im using a Pic micro for the delay, and a OPTo triac ( MOC 3020 ) for the switch. If I understand right a Traic will not shut off untill the current is removed so the flash Cap will be to low for a second flash.
Any suggestions for turning off the Triac?

Thanks for looking

williB · 7th February 2005, 03:20 AM

could you post the schematic you have so far , maybe we could make some suggestions..

Oznog · 7th February 2005, 04:03 AM

Oooh, good question!
I suspect- this is just a theory- that there's a low capacitance high voltage cap being fed from the main high voltage cap through a resistor, and the main cap is isolated from the tube by an SCR or the like which isn't turned on while the tube is triggered for the preflashes.

So the preflash only runs on the smaller cap. The resistor is sizes to be a large enough value to assure the flash quenches without draining the main cap, but small enough that the preflash cap will recharge off the main cap to fire a second time before the main flash.

1Steveo · 7th February 2005, 04:14 AM

I'm Not trying to design a new strobe circuit. What I'm trying to do is trigger a strobe to flash twice withend 400 ms.

williB · 7th February 2005, 04:54 AM

Quote:

The MOC301XM and MOC302XM series are optically isolated triac driver devices. These devices contain a GaAs infrared
emitting diode and a light activated silicon bilateral switch, which functions like a triac

http://www.fairchildsemi.com/ds/MO/MOC3020-M.pdf
so its not really a triac ..its a bilateral switch..designed to drive a triac..

Quote:

This optoisolator should not be used to drive a load directly.
It is intended to be a trigger device only.

Oznog · 7th February 2005, 07:27 AM

Quote:

Originally Posted by 1Steveo

I'm Not trying to design a new strobe circuit. What I'm trying to do is trigger a strobe to flash twice withend 400 ms.

Well, you are right about the triac problem. I don't see any way you could commutate it. You'd need a high voltage bipolar or a really HV MOSFET (MOSFETs this high are a bit rare). It needs to be able to handle an amp or so of surge current too.

williB · 7th February 2005, 01:54 PM

steveo , why not copy a circuit that allready does what you want..??

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7th February 2005, 03:04 AM	(permalink)
1Steveo	Simulate a Digital camera's Pre Flash? I need to have a Camera's Strobe Flash 2 rapid times aprox. 400 mill seconds apart. Im using a Pic micro for the delay, and a OPTo triac ( MOC 3020 ) for the switch. If I understand right a Traic will not shut off untill the current is removed so the flash Cap will be to low for a second flash. Any suggestions for turning off the Triac? Thanks for looking

7th February 2005, 03:20 AM	(permalink)
williB	could you post the schematic you have so far , maybe we could make some suggestions..

7th February 2005, 04:03 AM	(permalink)
Oznog	Oooh, good question! I suspect- this is just a theory- that there's a low capacitance high voltage cap being fed from the main high voltage cap through a resistor, and the main cap is isolated from the tube by an SCR or the like which isn't turned on while the tube is triggered for the preflashes. So the preflash only runs on the smaller cap. The resistor is sizes to be a large enough value to assure the flash quenches without draining the main cap, but small enough that the preflash cap will recharge off the main cap to fire a second time before the main flash.

7th February 2005, 01:54 PM	(permalink)
williB	steveo , why not copy a circuit that allready does what you want..??