Reference Diode
why does the Shockley diode equation say that current decreases with temperature?
According to the Shockley diode equation , current through a diode can be expressed as A* (exp(B*V/T) -1) where A and B are constants, V is the voltage across the diode and T is the temperature. It is known from experience and diode data sheets that current increases with temperature if the voltage is kept constant.
Isn’t Shockley’s equation contradicting common experience?
reference:
Diode equation: http://pvcdrom.pveducation.org/SEMICON/EQUAN.HTM
diode datasheet: figure 3 of http://www.nxp.com/documents/data_sheet/1PS301.pdf
The equation does not say that current decreases with temperature. It says the voltage required to produce a change of 10 times in current decreases with temperature. At 27degC current increases to 10 times when voltage applied is increased by 60mV, since kT/q = 26mV and 26^ (ln 10)= 60 mV. This is proportional to T. Thus at T= 200degK, or at -73degC, voltage needs to be increased by just 40mV to produce same ratio of currents.
So this 1/T applies to rate of change of current and not current. This principle is used in bandgap references. At 1mA, if 600 mV is required at 27degC, and 540mV is all that is required at 57 degC, current does increase for same voltage applied, by a factor of 10. Thus with 600mv applied at 57degC, current will be 10mA.. However, if 60mV was required at 27degC to increase current from 1ma to 10mA, voltage increase required at 57degC to increase current from 1 ma to 10mA will be higher = 66mV.
Tagged as:
reference diode,
reference diode 1.2 v,
reference diode 2.5 v,
reference diode 5v,
reference diode circuit,
reference diode laser,
reference diode lm336,
reference diode zxre125dr