Few Q's onMosfets/Transistors TO-220 and heatsinks

Discussion in 'The Projects Forum' started by DR1, Mar 2, 2015.

  1. DR1

    Thread Starter New Member

    Sep 13, 2012
    I'm building a slave board(shield) for an Arduino Mega with perf board which consists of 6 CC Drivers for two 3W RGB leds. I have questions on how to go about this since there isn't a whole lot of space. My CC Driver circuit uses two N-Channel Mosfets, a 10K resistor and a 9ohm resistor. Instead of using the TO-220 package I was thinking of using a Dual-Mosfet IC instead, to save on space. Since I need a heat sink on at least one of the Mosfets, Im curious how good the heat dissipation is for IC's compared to TO-220 package. I'd also like to keep the height of the board as low as possible, heat sinks make this difficult. Help appreciated on this.
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
    Unfortunately, a CC driver (especially if you are modulating the brightness of the LEDs) produces a lot of heat. The heat is proportional to the product of voltage across the driver times the current through it. The temperature reached by the driver chip is controlled by how the heat is dissipated by the chip, it's external heatsink, and to a lesser extent, to the copper traces it is soldered to. If you eliminate the heatsink, the temperature will climb.

    The ability of any chip/transistor to get rid of heat is called its thermal resistance from junction to ambient. It is shown a spec on the data sheet.

    Post a schematic of your driver, which actual parts you want to use, and specs for the LEDs. Power devices and small space are usually mutually exclusive...
  3. DR1

    Thread Starter New Member

    Sep 13, 2012
    Hi MikeML, this is the link with the CC circuit I am following:
    http://www.tbideas.com/blog/build-an-arduino-shield-to-drive-high-power-rgb-led/. You can see in the bottom picture how tall the heat sinks make the overall height of the board, I have about half inch of clearance to work with.

    Components I am using: 10k .5W resistor, 10ohm 1w current sense resistor, a 30n06l N-Channel Mosfet and a PN2222A NPN Transistor. I've replaced the NPN with another 30n06l to make sure the circuit still works fine in case I choose to get the dual mosfet IC. Looking at the Datasheet(http://dlnmh9ip6v2uc.cloudfront.net/datasheets/Components/General/FQP30N06L.pdf) the Mosfet's thermal resistance from junction to ambient says 62.5 degrees Celsius/W

    Here's info the 3W LED I am using: