Integrated Temperature Sensor μPC616 and Its Application

Abstract: The main characteristic of the μPC616 and its working principle were introduced in this paper. The typical application electric circuits based on μPC616 were given finally. Key words: temperature sensor; μPC616; linear variety PN junction integrated temperature sensor works by using the different current density differences of transistors at different temperatures. Its output form can be divided into voltage type and current type. The sensitivity of voltage type is generally 10mV/℃, and the sensitivity of current type is 1μA/℃. It also has the characteristic that the output power is zero at absolute zero. Using this characteristic, the absolute temperature value can be easily measured. μPC616 is a voltage output type PN junction integrated temperature sensor. 1μPC616 structure and working principle PN junction integrated temperature sensor has good output linearity, low output impedance, easy to interface with control circuit, can be used for temperature measurement and control, can also be used for thermocouple cold end temperature compensation and air flow rate detection. μPC series sensors are products of NEC, μPC616 is one of the typical products, its principle and internal structure are shown in Figure 1 and Figure 2.

The measurement range of μPC616A is -40～+125℃, while the measurement range of μPC616C is -25～+85℃. μPC616A uses a pair of well-matched transistors to operate at different current densities and uses the linear relationship between the difference in transistor VBE ΔVBE and temperature (T) to measure temperature. In Figure 1, the difference between the emitter and base voltage ΔVBE can be expressed as:

In the formula: K is the Boltzmann constant, I1 and I2 are the collector currents of transistors G1 and G2, q is the electron charge, and r is the emitter area ratio of G1 and G2, which is a constant.

From the above formula, it can be seen that if I1/I2 remains unchanged in a wide temperature range, ΔVBE is linearly related to the absolute temperature T. Figure 3 is the relationship curve between the PN junction temperature (℃) of μPC616A and its output voltage (V). It can be seen that there is a very good linear relationship between them.

As can be seen from Figure 2, the μPC616 circuit can be divided into a temperature sensor part, a voltage regulator part, and an operational amplifier part. The temperature sensor part has a temperature coefficient of 10mV/K, and the absolute value of its output voltage is 2.982V (corresponding to 298.2K) at T=25℃, so μPC616 can easily convert its output value into an absolute temperature value. The voltage regulator part has a temperature compensation circuit, so the output voltage is very stable. The performance of the entire circuit has the advantages of stability, reliability and good repeatability. This part of the circuit is equivalent to a Zener diode with a breakdown voltage of 6.85V. The operational amplifier has two functions in the circuit. One is that when μPC616 is used for temperature measurement, the inverting input terminal of the operational amplifier is connected to the output terminal to become a voltage follower. The output signal corresponds to the measured absolute temperature (K), and the corresponding value of the output voltage and temperature is 100K/V; the second function is that the inverting input terminal is used alone as the input terminal of the set value during temperature control.

2 Application of integrated temperature sensor μPC616

The application circuit of μPC616 is very simple. Figure 4 shows two basic circuits for temperature measurement. Pins 1 and 2 in the circuit are connected, and there is a temperature coefficient of 10mV/K between pin 3 and pins 1 and 2, and the output voltage V0=(10mV/K)×T, where T is the absolute temperature. As can be seen from Figure 2, there is a voltage regulator tube equivalent to 6.85V between pins 3 and 4. In order for the voltage regulator tube to work properly, the external power supply should be greater than 6.85V and a resistor should be connected in series. The value of this resistor is determined by the working current of μPC616 (about 1mA) and the external voltage. For example, if the external voltage is 15V, then:

In addition to measuring temperature, the μPC616 temperature sensor can also be used for temperature control. As shown in Figure 5, the sensor's pin 2 is used as the input terminal for the temperature setting value. By adjusting the potentiometer Rw, its resistance value is set at a voltage value corresponding to a certain temperature. When the external temperature exceeds or falls below this temperature, pin 1 will output a high level or a low level to complete the temperature judgment, thereby achieving temperature control or alarming.

3 Conclusion

The PN junction integrated temperature sensor μPC616 is similar to other integrated temperature sensors and is mainly used for the detection and control of ambient temperature, as well as the temperature detection, control and compensation in household appliances.

References
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