allanhurst:
probably not with a 28vdc supply,,, but it might be a lorry...Allan
I was thinking boat , but they generally do not have body return.
Not many modern small aircraft have a metal fuselage - they're usually composites.... so do you really need a grounded load?
And if this is for Boeing or Airbus, I take it you should know what you're doing, and would be unlikely to be using arduinos..
just curious.
Allan
allanhurst:
Not many modern small aircraft have a metal fuselage - they're usually composites.... so do you really need a grounded load?And if this is for Boeing or Airbus, I take it you should know what you're doing, and would be unlikely to be using arduinos..
just curious.
Allan
Haha there are no airworthiness concerns. Hence the "mock aircraft" description.
Without going into too much detail, it is something similar to a simulator which will be using a scrap aircraft which does have a fully metal fuselage. It will use many of the exact same systems as the real thing but they don't need to be work the same way and there is no certification requirement. In instances like this, we have had to "invent" a light dimmer because the real OEM one literally costs in the region of tens of thousands of dollars
Hi,
Why you do not install the mosfet instead supply voltage provide the ground to the light bulb. Then connect a resistor of 1k from the Ardiuno pin to the mosfet gate. Make sure the Arduino pin can do PWM. Also when your are working with high voltage it is a good idea to protect the micro pin with a zener diode of 5.1 volts. Since you are connecting the pin thru a 1K resistor if something goes wrong the zener will protect the pin from high voltage. Attached it is a drawing how you can do it. I think you do not need to use the TC4431 to drive the mosfet. You can adjust the intensity by controlling the pwm frequency.
Not the PWM frequency - the mark/space ratio.
analogWrite() does this for you.....
And the arduino limited drive current means the PWM frequency should be fairly low, as the switching time will be significant, which would lead to large transient losses with a high frequency. The standard 1kHz / 500Hz should be OK.
And I'd replace the zener with a pull-down resistor - say 10k - to ensure the mosfet is off when arduino power is removed.
But otherwise OK. Probably fine for driving filament bulbs.
Allan.
ps a simple 555 circuit would do what you want.. no arduino required.
allanhurst:
And I'd replace the zener with a pull-down resistor - say 10k - to ensure the mosfet is off when arduino power is removed.
You could put the 10k in parallel to avoid losing the protection of the zener. Low-side driving like
this needs a logic-level n-FET of course. Alternatively my high-side design is outlined in #7
tauro0221:
Hi,
Why you do not install the mosfet instead supply voltage provide the ground to the light bulb.
Hi Tauro, thanks for the input. I don't quite understand this but from your diagram, it looks like you're recommending an n-MOSFET. As I pointed out earlier, I need it to be a high side switch because the light assemblies earth through the body and thus don't have a dedicated negative wire.
Hi,
Then may you need something like this. Same circuit but using a transistor and a mosfet. See the circuit attached.
Thanks again for the input but it seems like you haven't read any of the other posts in this thread. That is essentially the exact circuit I had designed originally. I have said a couple of times now that I chose to try a purpose built driver instead as it was my understanding that something designed for the job would be superior to an NPN driver.
Just for fun, the 555 approach.
R2 and R38 are a 10k potentiometer shown near one end....
And r37 should be 100.
Allan
h555.pdf (22.3 KB)
Hi,
My apologies, maybe I missed one of the replays.
allanhurst:
Just for fun, the 555 approach.R2 and R38 are a 10k potentiometer shown near one end....
And r37 should be 100.
Allan
Interestingly enough, that was our first prototype before we were given permission to use Arduino
Why wasn't it satisfactory?
Allan...
Mainly, the brightness wasn't really linear. Down low it had a reasonable amount of control but then it would almost instantly go really bright around halfway on the pot.
It was almost certainly something we were doing wrong but that on top of the fact that we have a few other little things to simulate that need a bit more "brains", we figured why not just Arduino for all of it.
125W? I suppose many filament lamps in series / parallel.
-
Conductors of them creates a magnetic field that stores energy (in this case a little) and the law Lenz says:
I, the induced current
I have always opposed
Cause what I produced.
This gave rise to the high-voltage pulses.
The solution could be a diode in antiparallel to the consumer.
Internal diode transistor meets the protection requirements in theory but in practice it is not. -
The marks do not correspond with the transistor datasheet.
In similar cases the best results we have obtained with dedicated optocoupler (eg TL350).