Electronic – Parallel transistors for brightness control of large quantity of LEDs

ledparallelpwmtransistors

I'm working on an art project that consists of ~180 LEDs with about a dozen fading/flashing PWM patterns, with each pattern group/circuit controlled by a PN2222A transistor on the cathode side, with the transistor bases' signals coming from a microcontroller.

I would like to be able to control the overall brightness of all LEDs simultaneously (not really possible via the microcontroller with how I've programmed it), so I had the idea to use a few leftover transistors connected in "parallel" on the anode side to create a PWM brightness controlling "main bus" for all LEDs. The PN2222A transistors I'm using are rated up to 2A, so I figured putting 2-3 in parallel would allow the control of the LEDs high current draw (~3.6A @20mA each):

brightness control idea

I'm wondering if this looks like a reasonable solution? Or is there some reason not to do this in favor of a better way? Thank you very much!

Best Answer

You have the transistors as emitter followers so they are going to drop a lot of voltage. In a comment you said you have series resistors for each LED that are not shown in the schematic (necessary). Okay, they've been added but via an edit so all the comments about them being missing look odd .

I suggest using a single P-channel logic-level MOSFET. Low = ON in this case.

Somthing like an AOD417 which comes in a relatively easy to handle package.

At 3.6A with at least -4.5V Vgs it will be less than 55m\$\Omega\$ at 25°C so dissipation about 0.7W (will get warm, so a square inch or so of copper would be good). For more money, a https://www.vishay.com/docs/70297/sq40031el.pdf will be about 15x better.