LT SPICE THERMISTOR MODEL

Do you have a thermistor model for LT SPICE? Possible parameters would be the 25 DEG C resistance and the B 25 / 50 parameter so the resistance changes correctly when running .temp T1 T2 simulations?

  • +1
    •  Super User 
    on Nov 8, 2018 11:45 PM over 2 years ago

    Hello,

    I show one method using a stepped TEMP.

    The default of TEMP is 27°C if not specified. Be aware that TEMP is used by every component in your schematic - especially diodes and transistors change their behavior. You can avoid this, if you use another name e. g. TEMP1.

    .param R25=10k

    .param B=4000

    .param Tk=273.15

    .param T25=25

    Replace the value of the resistsor with this equation enclosed by curly braces.

    {R25*exp(B*(1/(TEMP+TK)-1/(T25+TK)))}

    .step TEMP 0 50 1

    Best regards,
    Helmut

  • Hi Helmut,

    Thank you, this is exactly what I need. I'm temperature compensating a BJT B-E junction so I want the TEMP command to also control the transistor models. I think ADI should make this a component with a menu  to enter R at 25 deg and B 25 / 50 for people like me who are not familiar with traditional command line SPICE.

    Marty

  • 0
    •  Super User 
    on Nov 12, 2018 8:20 PM over 2 years ago in reply to mrisso

    Hello Marty,

    Vishay and Infineon provides subcircuit models for their NTC-thermistors. These subcircuits also include the self heating of the NTC-resistors.

    Best regards,
    Helmut

  • Hi Helmuts,

    Again thank you. One quick question, in the method that you described above, is the B value the B 25 / 50 value? Some NTC thermistors list a few B values, B 25 / 50, B 25 / 85 etc.

    Also, the voltage across my thermistor will be less than one diode drop so I'm not concerned with self heating.

    Marty

  • 0
    •  Super User 
    on Nov 13, 2018 1:40 PM over 2 years ago in reply to mrisso

    Hello Marty,

    B25/50 menas you will get the best fit when you have this temperature range from 25°C to 50°C in your application. It may be still good for 0°C to 75°C.

    B25/85 is better when you have a wider temperatur range from 25 to 85°C or beyond. Maybe from 0 to 100°C.

    You will get more temperature measurement error beyond these limits.

    Some manufcaturers provide the coefficients for another formula with more coefficients e. g. for the Steinhart-Hart formula. These formulas are very precise for a very large range of temperature.

    Helmut