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TMP451: Suitable TO-220 transistor

user4878642
Prodigy 50 points
Part Number: TMP451

Hi,

I want to sense the temperature of a mechanical device remotely using a simpler solution than a thermocouple. I found the TMP451 with the remote diode as a possible candidate. The datasheet recommends the 2N3904/3906 which is available in TO-92. I could use that with a thermal adhesive, but for mounting and reliability purposes a screwable package like TO-126 or TO-220 would be better.

Do you have a suitable transistor to recommend in such a package?

Thank you,

  • 0
    TI__Mastermind 36920 points
    Hi,

    Thank you for choosing TI products for your design. Someone will get back to you soon.

    Aaron
  • 0
    TI__Expert 4905 points

    Hi user4878642,

    We have not tried a transistor in such a package. The TMP451 datasheet gives guidelines to follow when picking a transistor:

    If a discrete transistor is used as the remote temperature sensor with the TMP451, the best accuracy can be achieved by selecting the transistor according to the following criteria:

    1. Base-emitter voltage > 0.25 V at 7.5 μA, at the highest sensed temperature.

    2. Base-emitter voltage < 0.95 V at 120 μA, at the lowest sensed temperature.

    3. Base resistance < 100 Ω.

    4. Tight control of VBE characteristics indicated by small variations in hFE (that is, 50 to 150).

    So long as you follow those guidelines you should be fine. You will also need to run a test to determine what the ideality factor and offset is required for the transistor you choose. It would take me several weeks to do this perhaps you can pick one from your internal approved products list that would be cost effective for you.

    Where exactly are you trying to connect the TO126 package? We may be able to come up with an alternative solution is why I ask. Oh and also be careful as the collector is tied to the case (usually) and you will be using diode mode so check where you are connecting the case.

    Take care,

  • 0 in reply to Emmy Denton
    Prodigy 50 points

    Thank you Emmy,

    I chose a TO-220F package with a plastic tab to avoid electrical connection. In fact, I will do some testing with the Fairchild KSB1015 and KSB1366. They both have a high and fairly constant gain, but they don't give the base-emitter voltage at very low current.

    I am sensing the temperature of a pipe, which will be around -50C, and I only need a precision of +/-2C. I planned to brase a screw post to it so that I can attach the transistor with a nut. Thermal adhesive would probably work, but I'm not sure of the level of vibration such a link can sustain. It will be in a very noisy environment.

    _________________

    Fred

  • 0 in reply to user4878642
    TI__Expert 4905 points
    Hi Fred,

    You should try asking the manufacturer for the expected minimum voltage - they may be able to give you some simulation results. Testing them in a controlled temperature environment would be best. We use an oil bath. A +/-2C precision is very tight for this application - especially at -50C.

    Thank you for designing with TI products!

    Take care,
  • 0 in reply to Emmy Denton
    TI__Expert 4905 points

    Hi Fred,

    I'd like to refer you to this app note on remote diode sensing that has just been published:

    Optimizing Remote Diode Temperature Sensor Design

    Take care,