Actions
Forum Thread Details
  • State Not Answered
  • Replies 11 replies
  • Subscribers 13 subscribers
  • Views 2328 views
  • Users 0 members are here
Related

Heavy Load Switching with CodeBug

spannerspencer

Has anyone tried switching slightly heavier loads using the CodeBug's legs, either using a transistor or a relay? I'm working on something that'll need to switch two loads on and off that I'm pretty sure would melt the CodeBug if I did it directly (maybe 1-2 amps each). I'm thinking that something as simple as a transistor, switched from one of the legs, would do the job, but thought I'd ask if anyone's experimented this as yet?

Parents
  • 0

    A MOSFET like this would do you (assuming that your load is operating from a voltage less than 20V)

     

    http://uk.farnell.com/taiwan-semiconductor/tsm2312cx/mosfet-n-ch-20v-4-9a-sot23/dp/1864587

     

    The Vbe threshold is low enough that the 3V CodeBug outputs will switch it. The on resistance is only 27mOhms, so even at 3A it only has to dissipate a quarter of a watt (0.243W) which the package alone should manage.

     

    Connect the gate to the CodeBug output, the source to GND, and the drain to your load (with the other side of the load connected to the supply you're using). Remember to connect the ground of the CodeBug and the ground of the load power supply together.

     

    If the load is inductive (coil of some sort) include a catching diode as per the transistor circuit in shabaz's post.

     

    Observe static precautions handling the transistor before you get it wired in the circuit.

     

    If you want to prevent it turning on and off  before the CodeBug initialises its output pin ("flapping around" to use the technical term), include a resistor from the gate down to ground to keep the MOSFET turned off until it is actually being properly driven by the output.

     

    If you decide to take this approach, let us all know how you get on.

  • 0 in reply to jc2048

    Oh John, you're such an optimist image

     

    I read the same data sheet and come away with 40 - 50 mOhms (40 @ 2.5V gate drive + about 30% for being hot).

     

    But still good for 3A (just about at ambient = 25)

     

    MK

  • 0 in reply to michaelkellett

    Mea culpa!

     

    It was staring me in the face right at the top, too. But he/she did only ask for 1 to 2A, and the typical rds-on would be a bit better, and I presume this is experimenting and hacking rather than straight product design, so I think we'd get away with it. But you're right, it doesn't set a particularly good example.

     

    Curiously, by nature, I'm a right old pessimist.

     

    BTW Your post really confused me at first (calling me John) because when I'm logged in I see my real name (Jonathan) above my posts and I presumed that was what everyone else saw too. What an odd system.

Reply Children
No Data