Tuesday, December 23, 2014

Temperature dependency

All electronic components have some temperature dependency.
  • Resistance: 
    • Copper wire resistance has a positive temperature coefficient of 3900ppm/°C; for 100°C, the copper resistance changes 40%. 
    • Carbon film resistor has a negative temp co of -200ppm/°C and is worse for larger value resistors.
    • Metal film/Thin film/Thick film resistor has a temp co of +/-10ppm/°C to +/-100ppm/°C.  Testings show that the temp co is valid to -150°C.
  • Capacitance:
    • C0G or NP0 ceramic capacitors have very good temperature co, +/-30ppm/°C.  
    • X7R capacitors have +/-15% variation over the range -55°C to +125°C.  The capacitance typically peaks at the room temperature and falls off at both ends, but it could have very nonlinear temperature dependence.
    • Aluminum electrolytic capacitors have considerable temperature dependence.  The capacitance falls off significantly at low temperature because the viscosity of the electrolyte increases.
    • Solid tantalum capacitors have much less temperature dependence in comparison with aluminum electrolytic capacitors.
  • Inductance:
    • Core materials have nonlinear temperature dependence. 
    • The permeability of a ferrite core is usually maximized around room temperature, but falls off at the extreme temperatures.  At -180°C, the inductance can drop as much as 70%.
    • The powder core holds up well at the lower temperature. 
  • Diode:
    • Silicon PN junction forward voltage decreases with temperature, usually -2.1mV/°C.
    • Silicon PN junction avalanche breakdown voltage increases with temperature.
      • High voltage Zener diode is actually avalanche diode.  1N5245 15V Zener has a temp co of +820ppm/°C and 1N5271 100V +1100ppm/°C.  MMSZ5245B is tested to -150C and has a fairly constant temp co about 1000ppm/°C over temperature.
    • Silicon PN junction Zener voltage decreases with temperature.
      • 1N5221 2.4V Zener diode has a temp co of -850ppm/°C.
      • At around 5V Zener and avalanche balance out.  1N5231 5.1V Zener has a temp co of +/-300ppm/°C.
      • Temperature compensated reference Zener diode can have very low temp co, e.g. 5ppm/°C for 1N829 6.2V.  The temperature compensation is achieved with a forward diode in series.  At 5.6V, the temp co is about 2 mV/°C, similar to that of the forward diode voltage.
    • Schottky junction forward decrease with temperature.
      • -1.2mV/°C (ref 1)
  • Transistor:
    • Bipolar beta
      • Beta increases with temperature.
    • MOSFET threshold
      • Threshold decreases with temperature.
    • MOSFET Kp
      • Kp decreases with temperature.
    • MOSFET breakdown voltage
      • Breakdown voltage increases with temperature.

Reference:
1. Zetex, Temperature Effects On Silicon Semiconductor Devices, June 1995. (http://www.diodes.com/_files/design_note_pdfs/zetex/dn4.pdf) .

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