mosfet low output voltage

myk68 · 2017-11-19 22:17:16

Hi All

So I now have a 20 3W LED light matrix for the exposure.

I have a mosfet set to the Pi with 3v and signal input, currently 5v in for the light.

BUT

on start up 2.5v hits the lights, when I then open the shutter, this is where the light switch is controlled by( is that correct), then only 0.3v hits the lights.

I dont get it???

Is the shutter switch the wrong thing to use, there didnt seem to be anything else to use.
is the voltage lever then controlled by the servo pulses.

any advice would be appreciated. thanks for reading

Mike

bigfilsing · 2017-11-20 00:07:24

There are potentially quite a few issues re your set up. Any chance you could sketch your wiring layout?
The LED array needs a separate power source ( current limited)
The MOSFET switches this power source
The MOSFET is typically placed "downstream"- i,e it switches the negative side of the LED array to ground

myk68 · 2017-11-20 00:57:28

Hey Bigfilsing

mosfet_wiring.tif

Its fairly simple on the set up I think maybe the power source is best not being the pi itself but I checked the incoming and its 5v, just dont get why its not passing it through
the mosfet is the wingoneerIRF520 from amazon, tried 2 and both the same.
swapped the power roound so the 3 v was to the lights and the 5v to the signal and the output v went to .1v, so seems to be a fraction of the input v.

glad to hear anything

Mike

bigfilsing · 2017-11-20 03:42:26

A stepper driver draws way too much current to be powered from the Raspi directly. Added to which the stepper driver needs at least 12VDC to drive a Nema 17.

I would normally use a 12VDC power supply Then use a buck converter to power the Raspi and wire the stepper driver directly to the PSU ( usually with an in line fuse)

Then a similar buck / boost converter with current limiting for the LED array

I couldn't see/ open your "mosfet_wiring.tif " ??

Last edited by bigfilsing (2017-11-20 03:43:47)

myk68 · 2017-11-20 20:44:16

NO no the stepper is powered by a seperate 12v supply, its only the light at the moment I have through the Pi 5v pins, just while i get it going then more is available seperately.

Ill try this jpg file for the sketch of the mosfet. its looks right to me????

bigfilsing · 2017-11-21 02:42:24

Any chance you could post a few more details on your "MOSFET" and LED array?

A lot depends on how your LED array is configured and powered. Typically the LEDs have their own power supply ( often called a driver)

You should consider joining https://plus.google.com/communities/109 … 7401814291

There's a ton of info there

bigfilsing · 2017-11-22 05:12:37

so from your sketch it would appear you have one of these

and this is the corresponding schematic

bigfilsing · 2017-11-22 06:11:47

you should end up with something like this

peter_john · 2018-03-22 16:58:18

Hi...i am a new user here. In my case I normally use a 12VDC power supply Then use a buck converter to power the Raspi and wire the stepper driver directly to the PSU.Then a similar buck / boost converter with current limiting for the LED array.

surface mount pcb assembly

Last edited by peter_john (2018-04-19 17:41:23)

nanoDLP

#1 2017-11-19 22:17:16

mosfet low output voltage

#2 2017-11-20 00:07:24

Re: mosfet low output voltage

#3 2017-11-20 00:57:28

Re: mosfet low output voltage

#4 2017-11-20 03:42:26

Re: mosfet low output voltage

#5 2017-11-20 20:44:16

Re: mosfet low output voltage

#6 2017-11-21 02:42:24

Re: mosfet low output voltage

#7 2017-11-22 05:12:37

Re: mosfet low output voltage

#8 2017-11-22 06:11:47

Re: mosfet low output voltage

#9 2018-03-22 16:58:18

Re: mosfet low output voltage

Board footer