The junction voltage of crystal diode or triode PN junction changes with temperature. For example, every time the temperature rises by 65438 0℃, the junction voltage of the silicon tube PN junction drops by -2mV. Using this characteristic, a diode (such as a glass-encapsulated switching diode 1N4 148) or a silicon triode (which can connect the collector and the base in a short circuit) can be used as a diode to make a PN junction temperature sensor. The sensor has good linearity, small volume, thermal time constant of 0.2-2 seconds and high sensitivity. The temperature range is -50-+ 150℃. The typical temperature curve is shown in figure 1. The characteristics of the same type of diode or triode are not exactly the same, and the interchangeability is poor.

Figure (2) is a digital thermometer with PN junction temperature sensor. The temperature measurement range is -50- 150℃, the resolution is 0. 1℃, and the accuracy can reach 1℃ in the range of 0- 100℃.

In the figure, R 1, R2, D, W 1 constitute a temperature measuring bridge, and its output signal is connected to a differential amplifier A 1, and the amplified signal is input to a 0-2.000 V digital voltmeter (DVM) for display. The amplified sensitivity is 65438+1100mv/℃. A2 is connected as a voltage follower. With W2, the gain of amplifier A 1 can be adjusted. ?

The working current of PN junction temperature sensor should not be too large, so as to avoid the temperature rise of diode itself affecting the measurement accuracy. The general working current is 100-300ma. It is complicated to use a constant current source as the working current of the sensor. Generally, constant voltage source is used for power supply, but it must have good voltage stabilization accuracy.