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Driving LED strip from GAD27 PWM pin

gfb

Well Known Member
Looking at driving a cockpit LED strip off the GAD 27 PWM pin. From the docs, it can only sink up to 500mA and it seems the average RGBW LED used in strips out there pulls 20mA per color and 25mA per white.

At full brightness I'm looking at only being able to power 20 white LED's or 25 individual color LEDs, which seems a bit low considering the usual strip for sale is 60 LED/m with 144 LED/m being fairly common. This is for my dash eyebrow so about 1m long.

How are others doing this? Put a transistor in place to drive the power?
 
I bought the LED strip from Vans (red and white) and use the GAD 27 to control each color without use of any additional resistor.

I power white off a cabin lights circuit and red off a panel lights circuit with the GAD 27 controlling ground for either on one of the PWM channels.
 
How many LED/m is that and how bright does it get? I suspect I don't need nearly as much lighting as I put in, but it's what I found for an RGBW.
 
I power white off a cabin lights circuit and red off a panel lights circuit with the GAD 27 controlling ground for either on one of the PWM channels.

Notice what is being said here: The LED power comes from the bus through a circuit protection device to the "+" side of the LED's. The "-" side is connected to the GAD-27 PWM inputs. It's opposite of how we typically wire varying-voltage lighting control, as with incandescent (and sometimes LED) lighting, but that's the way it is supposed to work.
 
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