lednpntransistors
I am quite new to electronics. I am trying to control three LEDs with an Arduino using a transistor.
I was wondering what the base current limiting resistor value should be.
I looked around the internet and some YouTube videos and came up with these calculations, but I don't know if I am correct or not.
I am using a 2N2222 NPN transistor and I am taking 100 as GAIN (B).I came up with 1.4K. Am I right or am I missing something?
LED Resistors are 220Ohm
That quote is just wrong.
That circuit is correct, but not for your application as it will require about 8V minimum input to give 6V at the output.
It works by supplementing the output current of the 78xx (7806 for 6V) regulator if the regulator takes significant current (about 600mA) with additional current through the PNP transistor.
Your Lipo batteries will not have a constant output voltage, they will probably vary between 8.4V when fully charged down to about 6V or even less when discharged.
What do you need the 6V for? How much current do you need? What is the acceptable voltage range for the load?
Thanks for not posting the Fritzing diagram as they drive some of the regulars here apoplectic. There's a schematic button on the editor toolbar if you want to sketch something out for appraisal.
Typically in common anode setups, writing a value of 255 to a PWM pin indicates OFF and writing 0 is full brightness. These controls seem to be inverted now with 0 being OFF. Is this normal behavior?
0 is normally off. 1 is on. 100% PWM would be "on all the time". You can think of it as the % time power is applied.
The brightness steps are out of control. Writing 1 to a RGB pin creates a fairly bright light, and anything above 3 is maximum brightness. For my color reproduction to be effective, I need at least 100 brightness steps as I had in my previous setup where only 1 LED was used and no NPN transistors were in the circuit.
It sounds as though there's something wrong with your PWM output configuration or code. Post the relevant bits in your question and be sure to use the "code" tag.
simulate this circuit – Schematic created using CircuitLab
Figure 1. Q1 lights the red channel. Triplicate for green and blue.
Best Answer
Actually, with \$\beta\$ = 100 you would end up with an \$I_B\$ of 0.3 mA (not 3 mA).
BUT as you want to switch the NPN fully on, it is actually a good choice to assume a much lower \$\beta\$, like \$\beta\$ = 10 like you did (by mistake).
Why?
Because you want the NPN to operate in saturation (not active mode). So you do end up with a correct answer. Any value for R between 1 kohm and 5 kohm would be correct in my view.