optoisolated adapter

Posted on Feb 5, 2014

This design adapts such a high voltage flash for use on a low voltage camera by using an optocoupler to electronically isolate the camera`s contacts from the high voltage. It can then be triggered by the camera using the 6 volt supply from the flash unit`s batteries, but also works at a lower voltage. The use of a triac optocoupler has the added advantages of using fewer parts than

optoisolated adapter
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other optocoupler designs and can use the power from the flash`s trigger circuit to fire the SCR switch instead of a separate power source. The adapter circuit can be inserted into the lines inside the flash unit going between the flash trigger circuit and the flash unit`s contacts as shown below. Since there are only 4 small parts in this circuit, there is a good chance that you can build it right into the available space inside the flash unit`s case. o- | - (+) Flash hot-shoe contacts | Flash trigger circuit o- | - (-) |/ Cut and insert adapter circuit below +-+ R2 (-) o-(1)-+ +-(6)-//-+-o Flash Trigger (+) | | OPTO1 | | 5. 6K |A To Hot-Shoe | _|_ _|_ | _|_ (and camera) | _\_/_-> _\_/_/_\_ (5)NC _\_/_ SCR1 | | | | / | 400V, 6A (+) o-+ +-(2)-+ | | |G | K (RS#276-1020) | | NC(3) +-(4)-+ | / | +-+ | R1 | Optotriac +-o Flash Trigger (-) 330 / | MOC3010 | (RS#276-134) | | o o (+) (-) To 6V Battery (Flash unit battery pack) The camera shutter shorts the hot-shoe contacts, causing current to flow from the 6V battery through the IR-emitting diode at pins 1 & 2 of the OptoTriac. The current is transferred via light pulse which switches on the triac at pins 4 and 6 of the OptoTriac which is powered by the voltage from the flash trigger circuit. Current flows into the gate of the SCR, switching it on and causing discharge of the flash trigger through the anode and cathode of the SCR. The 330 ohm resistor (R1) limits the current...

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