I've 1W power LED which is connected via ULN2003A to PWM pin. ULN2003A has saturation voltage about 1V. My power source is 5V, so should I calculate resistor for 5V or for 5V-1V=4V (LED current is 320mA)?
P.S. It seems that there is no LED driver, except switching regulators which work with so low voltage drop, so I'll use a resistor.
so should I calculate resistor for 5V or for 5V-1V=4V (LED current is 320mA)?
Yes you should include it, however you also must include the Vf drop of the specific led you are using.
For your example lets assume a 3vdc Vf drop for the led assembly as I don't know the spec for your led.
R = (5v - (1v + 3v)) / .320 = 3.1 ohms
By the way, those high current led assemblies almost always recommend not to try and use a simple series current limiting resistor to maintain proper current control. They demand a constant current driver to operate safely.
retrolefty:
By the way, those high current led assemblies almost always recommend not to try and use a simple series current limiting resistor to maintain proper current control. They demand a constant current driver to operate safely.
The problem is that I ended up with three possible options for LED drivers: