What trigger voltage and current are safe for a Sony A7R/A7R II hot shoe or PC-sync flash connection?
Asked 8/20/2021
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I’m building a DIY flash and want to trigger it from a Sony A7R/A7R II via the hot shoe or PC-sync connection, using a 3.5mm jack on the flash side. I’ve measured around 3–5V on a rental strobe before, so I was planning to use about 5V for the trigger circuit.
What I can’t find is the safe current level for the camera’s trigger connection. My regulator options are rated for 50mA or 120mA output, and I want to avoid damaging the camera.
Does the camera determine the trigger current draw, or should I explicitly design the trigger circuit to limit current? What voltage/current range is typically appropriate for modern Sony mirrorless flash triggering?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
4y ago
2 Answers
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Typical trigger signal in modern cameras/flashes is around 5v @ < 10mA.
Sony lists flash compatibility for all DSLR/SLT bodies as being the same. The multiport shoe is powered at 3.15v @ ~1A (fused at 1.6A). And the current (compatible) Sony flash HVL-F60RM is rated at 6v, 1W which is .167A (167mA).
I think your 50mA should be fine, but lower would be better. The 120mA is getting close to the max I think, and is far in excess of what should be needed. I would drop both down to ≤ 10mA with current limiting resistors; you can always increase it later.
But the safe bet would be to get a compatible sony flash and actually measure the trigger amperage... you can even rent one.
Originally by user70370. Source · Licensed CC BY-SA 4.0
user70370
4y ago
0
Generated from our catalog & community — verify before relying on it.
Design the trigger circuit to use very little current. The regulator’s maximum output rating (50mA or 120mA) is not the same thing as the trigger current the camera should see.
From the answers here, modern flash trigger signals are typically around 5V and usually well under 10mA. One responder noted studio strobes at 4V/3mA, and another described a speedlight trigger that is under 10µA except for a brief ~6mA pulse. Based on that, 50mA and especially 120mA are far higher than should be needed.
The safest approach is to current-limit your trigger circuit and aim for ≤10mA, preferably much lower if your design allows. Adding a resistor or otherwise limiting the trigger path is the right way to protect the camera. You can always increase current later if testing shows it’s necessary.
So: use about 5V, but design the trigger to draw only a few mA or less, not tens or hundreds of mA.
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