We have used OEM parts from Airbus, parts that are old, so old that the backlight of most cockpit panels is made of tiny incandescent bulbs, each one consuming ~200mA. Adding up the overhead panel it consumes about 30-40A for the entire overhead (at 5V DC).
Originally it uses 5VAC (RMS) but in order to avoid complications we just use DC.
In order to turn the bulbs on and off, for the MIP that requires about 30A, I use 4x 10A relays in parallel in order to not overload them.
The thing is that apart from turning them on and off, in real life you can also regulate them with a potentiometer that's on the pedestal panel.
The thing is imagine I read that on an Arduino, the only thing I can output is PWM. I would need some kind of DC voltage regulator (from 0 to 5V) that can be controlled with PWM and that allows me to use high current like 30-50A at 5V.
Is there something even close to that? Maybe if it supports only i.e. 10A, I can place some in parallel or something similar. Any ideas?
Drive a suitably sized logic level N type mosfet, or parallel combination of logic level N type mosfets, from the Arduino pwm signal via a series gate resistor and gate pull down resistor.
There's no code related to the question, neither links nor schematics...
I want to use a PWM output from an Arduino to control "something" (this "something" is what I haven't figured out) that regulates DC voltage within 0 and 5V, and this "something" should be able to handle about 50A 5V or at least be stackable.
The think is that I'm really new in electronics, I'm a software developer but I just know the very very basics of electronics, so I don't know how to find a part number for a MOSFET that would be suitable.
I already tried to look for it because I read some other answers from other posts/forums.
I saw IRL540 but I read that it's not intended for 5V, any suggestion?
The standard operation of cockpit lights is one switch to turn all lights on so the operator can find any burned out lights. Have you implemented this, yet?
Although incandescent lights can also be driven directly with PWM, i think it will shorten their lifetime considerably.
I would go for a bunch (or just a few with significant heatsink) of power transistors like TIP120 driven with a filtered PWM signal.
(nb 10uF capacitor should be bigger if more power required, probably closer to 1000uF for maximum current)
I do actually think it would be best to subdivide the backlight system into groups, but i guess you don't have to and you can just bridge them. The risk is though that if 1 transistor fails for whatever strange reason, they will all fail in a cascade of overheating.
Sounds like you misinterpreted what you read, or whoever wrote what you read misinterpreted what they read. IRL540 part is fine for switching anything up to 100V (Vds) and has a gate threshold of 1~2V so should be be fine to drive with the 5V Arduino pwm signal.
You don't need anything like 100V, so a similar MOSFET but with a lower Vds might have a lower Rds meaning you can put more current through it without needing a heatsink or perhaps using fewer MOSFETs in parallel to switch your entire panel. For example IRLZ44
I can imagine what might shorten the life of incandescent bulbs might be constant changes in the temperature of their filaments, causing thermal "shocks". Their thermal mass will be very low, but they inevitable will have some thermal mass, so a high frequency of pwm should keep their temperature from fluctuating too much. And they are designed to use AC, so their temperature would be fluctuating continuously in normal use. But I'm no expert in driving incandescent bulbs, but maybe someone on the forum can confirm if what I'm suggesting is correct. @Grumpy_Mike or @Paul_B , perhaps?
Those would have a very high voltage drop, so would require a higher voltage PSU to compensate. Even then, they would dissipate large amounts of heat, so you would need a lot of them to switch the whole panel.
Actually it's the switching 'on' from nothing repeatedly, where the bulb has less resistance while there is no current flowing, causing a current spike. A square wave like PWM is much more damaging than a sinus wave of AC where the voltage increase and therefore the current increase is gradual.
The reason i am suggesting transistors instead of mosfets is that in many cases they will be 'half-open' which will generate a lot of heat in the mosfets as well. If you actually switch them with PWM then of course a transistor is not the proper choice.
+1. "Normal" incandescents are driven with 50 or 60 Hz AC (equivalent of 100 or 120 Hz PWM). Dimming is done by phase angle modulation; the dimming increases their lifespan, because less power -> less heat -> less filament evaporation -> longer life.
The reduction in lamp life from D.C. operation is from filament
"notching". The Tungsten surface becomes very irregular after
burning, appearing very faceted from the formation of notches
at grain boundaries. These notches reduce the filament
diameter at various points, creating hot spots, and faster
evaporation and reduced filament strength become the
dominant factors influencing reduced lamp life.
Filament notching is predominant with fine wire filament lamps
with operating temperatures that are lower than that for significant
normal Tungsten evaporation. Because of this, operation
at a voltage lower than rated voltage usually does not yield the
increase in life normally expected.
I am not sure if it means DC itself reduces lifetime on its own or if it is only at reduced drive.
In either case I don't think PWM should further reduce the lifetime compared to pure DC dimming.
Even with a relatively low RDS(on) of 0.0175 ohms @ 5.0 volts, that has to dissipate 63 watts at 60 Amps meaning either a relatively large heat sink or an even better mosfet.
Incidentally, are these bulbs grounded to the chassis ? Depending on how these are wired, you may need a P channel device.
Yes, I mentioned IRLZ44 only as a relatively better option than IRL540, which has a higher Rds. But it's still not ideal. As @bluejets mentioned in post #3, multiple MOSFETs could be used to spread the load, and heat, and might also allow independent dimming of different parts of the whole backlight, if that was desired.
Hmm, chassis GND and backlight GND are both connected yes, but it has it's own GND, I mean, it's connected outside, not welded to the chassis.
It has a more or less flexible PCB with all the lights welded and a connector that passes trought a plastic non conductive layer of the chassis, if you are curious about how Airbus done it I can send photos haha
The question was to determine if the switching can be done on the low side.
At the moment you are using relays. Do these relays switch the positive rail of the power supply to the bulbs. Is it also possible to switch the negative rail instead ?
In fact all the korry switches (the buttons/switches) that have bulbs inside are switched on GND.
Those korry's light has only 3 possible states: 1.OFF, 2.DIM and 3.BRT, BRT is 5V, DIM is 3.3V and off is.. off.
So I switch GND to manage each individual bulb and on the supply part I supply 5V or 3.3V selected with a relay depending on what you select on the panel (DIM or BRT).
