I currently have an LED light that has red and yellow lights. They are not to be on at the same time for my application. Unfortunately they are 12V+ switched so I had to use a combination of N and P MOSFETS to switch them using Arduino 5V.
Right now I have a total of four MOSFETS to control these lights (1 N channel and 1 P channel for each color). I'm using the Arduino to turn off one circuit when turning the other circuit on.
Four MOSFETS take up a lot of room on my PCB and I only ever need one color on at any given time. Is there some kind of component that can "divert" the 12V power from one path to another? I can't seem to find what I'm looking for?
So I'm using a N channel and P channel mosfet to high side switch 12V+ using my Arduino as TTL signal.
However, I have this circuit for both yellow and red LEDs and it's taking up a lot of room. So four MOSFETS total right now.
Since only red or yellow will be on at any one time, can I somehow only use this circuit once and put something after this circuit that can direct the voltage to the red pin, or the yellow pin?
Since it is switching only 12V the Zener diode is never conducting. When you remove the Zener diode you may also remove the resistor between Gate of P-MOSFET and Drain of N-MOSFET.
How is it possible you cannot switch GND but only 12V connection?
EDIT:
You may try this "evil" circuit. It should work for logic level MOSFET with the right Zener diode as D1 (~8V when using 5V Arduino and 12V LED supply). But there are many possible problems - for example when Arduino is not powered while the 12V power is active. Or if the 12V is "sometimes 14V and sometimes only 10V" in reality.
First wire is ground.
Second wire requires 12V+ to turn on red LEDs
Third wire requires 12V+ to turn on yellow LEDs
Fourth wire requires 12V+ to dim the LEDs. Otherwise they are default on the bright setting.
I can low side switch the ground, but I would still have to switch power between the red and yellow 12V+ wires to select red or yellow. Therefore, at the moment I have ground permanently grounded and I am using that circuit (twice) to control the red and yellow 12V+ wires.
This was the explanation of the circuit I am using which I found to be quite useful:
No, you're stuck with that many transistors. That module won't let you do any tricks like putting the two LEDs in series.
But you aren't stuck with that many component packages. You can probably find 3 power MOSFETS in a single package. Maybe even with the drivers built in.
Hi,
It looks like the 3 inputs are low current, control inputs.
How much current is in the control wire when you connect it to +12V.
Have you thought about using opto-couplers, one for each of the three inputs.
Makes your component count low and provides isolation between Arduino and LED controller.
Current through wire for red LEDs is 300mA
Current through wire for yellow LEDs is 300mA
Current for dimmer wire barely registers on my power supply. A few mA probably.
I've never used opto-couplers but I could look into it. How will they reduce component count? My knowledge of them is limited to the idea that they eliminate a physical connection between the high and low circuitry to protect the uC and other sensitive components.
What transistors do you use? There are very tiny SMD MOSFETs rated for even larger currents. Also the N-MOSFET does dissipate negligible power, it does not need to be large.
