In my project I have a microcontroller which has to light 3 groups of LED. Group A has 3 LED, Group B has 2 LED, Group C has 1 LED. There are all the same LED. In each group the LED are in series.
Let's consider group A :
VCC is obtained from a positive voltage regulator. The lighting of the group is controlled by an MOSFET which acts as a switch. The microcontroller is driving this transistor open or close.
I have never done this before so I have questions :
- How do I know which voltage I have to appply with the regulator for each group? Is it the sum of each forward voltage ? Let's consider each LED has a forward voltage of 3 V. I would then need to apply 9 V, 6 V and 3 V?
- Do I need a series resistor in each group?
- How do I know the current which will be drawn by the LED in each group? How do I set the current to 1 A in each group for example?