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I'm in the process of making my own home-made camera flash. I'm now designing the "trigger circuit" that will be using a 3.5mm jack as my preferred connection to the camera's PC sync or hot shoe.

I know that flashes's trigger voltage varies between different brands but I decided to use 5 volts for my design, as I have managed to rent a godox 300W last year and I remember that its using around 3 ~ 5 volts (yes, I measured it with a voltmeter), and this particular flash works fine on my A7R camera, so I'm good on using that voltage value.

Now, my problem is the MAX "current rating" of the PC sync / hotshoe connection of the camera. I have no idea and for whatever reason - google cannot give any definitive answer.

I asked because I will be using two different regulator ICs to step-down my battery voltage level, and the ICs are giving me two different output current rating - one is 50mA and the other is 120mA.

Will these values work fine on my A7R or with mirrorless cameras in general? Last thing I want is connecting the flash to the hotshoe and then hitting the shutter button but only to smell the magic smoke of a burnt circuit of my camera's trigger circuit.

I know that the princicples with regards to current in electronic devices - is that the Load is the one to decide whatever current amount it would draw. In this case, the camera will be the load (I assume) so the camera should be safe from getting destroyed - if the output current of 50mA or 120mA is not enough, the flash would not work.

BUT I just wanted to be sure. I don't want the added trouble of fixing my camera's trigger circuit. So for anyone who knows the current ratings of sony alpha cameras or mirrorless in general, please share your inputs. Thanks!

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  • \$\begingroup\$ This is likely well beyond the purpose of this group. See this \$\endgroup\$
    – xenoid
    Aug 20, 2021 at 16:44

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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.

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  • \$\begingroup\$ Awesome. Thanks my man. That's right on the ballpark values of my design. I will be pulling it down to ~10mA with a .05% resistor. \$\endgroup\$
    – jtrner
    Aug 21, 2021 at 3:07
  • \$\begingroup\$ Oh btw, if I may ask - you still have the link for that 5V, 10mA specs? Did you read it somewhere or its just something out from experience? Its bugging me why camera manufacturers are keeping this thing a secret.. \$\endgroup\$
    – jtrner
    Aug 21, 2021 at 3:18
  • \$\begingroup\$ @jtrner, I've read many things that say "a few mA." I tested my Godox and Nikon flashes and got as high as 27mA, but most readings were down around 7mA when it flashed. And this link says the PC port for a Canon is at 9mA. dpreview.com/forums/thread/2354429 \$\endgroup\$
    – Steven Kersting
    Aug 21, 2021 at 12:55
  • \$\begingroup\$ This is the kind of post that I'm looking for, thanks man! \$\endgroup\$
    – jtrner
    Aug 22, 2021 at 4:10
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Your power supply current rating should have no bearing on your trigger current. You should be able to design a trigger circuit that utilizes less than 1 mA. My studio strobes are 4.0V, 3mA for the trigger, my speedlight is in the < 10 microamps, but does a 10nF capacitive dump through a 820 ohm resistor from 5V (6mA pulse) through the camera's flash trigger.

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  • \$\begingroup\$ Thanks for the inputs man. Will keep note of that. What cameras are you using those probes btw? \$\endgroup\$
    – jtrner
    Aug 21, 2021 at 4:30
  • \$\begingroup\$ @jtrner I have the schematic for my Nikon SB-600 speedlight. My studio strobes, I measured the voltage & current of the trigger as well as profiled the light energy output for each power setting. You should be searching for repair manuals of various strobe/speedlight systems to see how they do their trigger circuits. \$\endgroup\$
    – qrk
    Aug 21, 2021 at 17:54
  • \$\begingroup\$ Yeah, thanks the tip. Looking at one right now. \$\endgroup\$
    – jtrner
    Aug 22, 2021 at 15:38

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