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XTR110 external mosfet

David Prince92104
Prodigy 250 points
Other Parts Discussed in Thread: XTR110

My XTR110 is set up for 0-5vdc in and 4-20mA out, and powered by 24vdc. I have been using the IRF9510 Pmos, but noticed its VGS is to low. The temperature of the IRF9510 at 20mA was 109.5F. I then tired the FQP2P20 Pmos and at 20mA its max temperature was 111F. I also tried the FQP7P06, which had a max temperature of 111F at 20mA. All the mosfets are capable of handling 2+ amps. Is this the reasion for the high temperatures at low currents?

What mosfet temperatures have other people seen?

  • 0
    TI__Guru 62945 points

    Hi David,

    Power dissipated in a MOSFET is not related solely to the current flowing through it, but a combination of the current flowing through it and the voltage drop (Vds) across it.  What value are you using for your load resistor? 

    That said, I looked at the PMOS devices you've listed and these are large devices that shoudn't have any issues in this application.  What temperature are you operating at?  Does your circuit and output current fuction as desired?  Are there any other strange circuit behaviors you've noticed? 

    Please share a schematic and layout if possible and we will try to make sense of the behavior.  

  • 0 in reply to Collin Wells
    Prodigy 250 points

    To get the numbers in the first post i was just using the current meter as the load, causing a VDS of 22.49v.

    The following is data collected from the circuit built on my bread board. Load was 500 ohms plus the current meter, 24vdc, no heatsink. All testing was conducted at 70F. R46 is a 10K. Circuits are acting fine.

    IRF9510  

    VDS = 12.4 @ 20mA 90.3F with VGS=3.7

    FQP7P06

    VDS=12.45 @ 20mA 92.3F with VGS=3.246

    FQP3P20

    VDS = 12.43 @ 20mA 91.2F with VGS=4.60

  • 0 in reply to David Prince92104
    TI__Guru 62945 points

    Hi David,

    I didn't read your first post very carefully and thought you were referring to your temperatures in degrees Celsius.  I'm pretty sure your temperatures are correct and very reasonable.  From room temperature to 100F is only 20-25 degrees F which is only 11C.  It won't take too much power dissipation to cause an 11C temperature increase so everything sounds normal and I apologize for the previous alarm.