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Faster switching speed from mosfets in existing circuit/PCB
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fsr:
It seems like the 2n7002 are controlled by what seems to be a long wire. Could the slowness to turn be caused by something like wire inductance?
blazini36:

--- Quote from: fsr on December 19, 2018, 09:38:12 pm ---It seems like the 2n7002 are controlled by what seems to be a long wire. Could the slowness to turn be caused by something like wire inductance?

--- End quote ---
I don't think so. The cable that the remote wire is in is about 7 or 8 feet long, it's a 22 or 24awg 4 wire shielded cable. The cable that runs the VOUT to the strobe is just as long going back to the same place (2 wire 18AWG). The thing is that they are the exact same cables that ran the remote and VOUT with the AC-DC Driver and the External SSR. Unless the length of the wires is affecting the Mosfet differently than it did the SSR, I'd say it's probably not the cables.

I will say that I don't expect the exposure to be as fast as it originally was at 30-100us depending on the amount of light diffusion used. The power output of the DC-DC drivers is lower so the exposure time will be longer due to less available light. I would say I'd expect it to be ~400us max. ~900us implies a delay, and the exposure trigger is slightly out of sync with the strobes flash.

I had to cut this clip short but it illustrates the necessity for the quick strobe switching, This is on the original LED Driver setup.
https://www.dropbox.com/s/66sjfddnhj5u0mg/Video%20Sep%2007%2C%209%2014%2016%20AM_0.mov?dl=0
blazini36:

--- Quote from: nick_d on December 19, 2018, 06:50:36 am ---Interesting observations. Observation beats theory :) And your reasoning makes a lot of sense. I agree that switching the other side of the LED may be an option. I suggest to breadboard it first and make sure all is OK. By disconnecting the LED you are asking the constant curreny source to provide an infinite voltage. It should go smoothly in and out of voltage limiting, but you do not know for sure until you try.

Another suggestion is to use a different but similar LED driver if you can find one with a shutdown pin as you require.

Keep us informed how it goes.

cheers, Nick

--- End quote ---

RECOM makes some DC-DC drivers that I thought about trying but it seems they are only step down. I'm trying to consolidate everything to being run off a single 24v power supply so I need boost drivers. I did order some SMD SSRs, I will just assemble another one of the prototype PCBs and scratch out and jump some traces to make the SSR work on the output as a test before I route a new PCB for the SSRs. My soldering skills are much better than my breadboarding, tends to be a huge mess of jumpers lol
fsr:

--- Quote from: blazini36 on December 20, 2018, 12:40:11 am ---
--- Quote from: fsr on December 19, 2018, 09:38:12 pm ---It seems like the 2n7002 are controlled by what seems to be a long wire. Could the slowness to turn be caused by something like wire inductance?

--- End quote ---
I don't think so. The cable that the remote wire is in is about 7 or 8 feet long, it's a 22 or 24awg 4 wire shielded cable. The cable that runs the VOUT to the strobe is just as long going back to the same place (2 wire 18AWG). The thing is that they are the exact same cables that ran the remote and VOUT with the AC-DC Driver and the External SSR. Unless the length of the wires is affecting the Mosfet differently than it did the SSR, I'd say it's probably not the cables.

I will say that I don't expect the exposure to be as fast as it originally was at 30-100us depending on the amount of light diffusion used. The power output of the DC-DC drivers is lower so the exposure time will be longer due to less available light. I would say I'd expect it to be ~400us max. ~900us implies a delay, and the exposure trigger is slightly out of sync with the strobes flash.

I had to cut this clip short but it illustrates the necessity for the quick strobe switching, This is on the original LED Driver setup.
https://www.dropbox.com/s/66sjfddnhj5u0mg/Video%20Sep%2007%2C%209%2014%2016%20AM_0.mov?dl=0

--- End quote ---
Well, the SSR could react differently, because they're optocoupled, so that any driving circuit is internal to the SSR. With a mosfet directly connected, you depend on the driving circuit to charge/discharge the gate fast enough.
ealex:
i don't think the LED drivers you are using are intended for what you want.
I can't find in their datasheet anything related to timing, etc.
the PWM dimming input can have a RC filter inside the module, and that adds delays, and then you have the control loop delays / internal soft-start / etc - you have a "black box" with an unspecified behavior.

if you only use the leds as a strobe light, why don't you have a constant voltage power supply, use some properly sized resistors for current limiting and a N-FET + proper driver for a low side switch ?
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