DC power supply, also known as DC regulator. It's mostly an alternating voltage supply voltage when the output voltage or load resistance AC power supply voltage, direct output voltage regulator can maintain stability. The voltage regulator parameters stability, ripple coefficient and response speed. The former indicates input voltage variation on the output voltage. Ripple factor expressed in nominal operating conditions, the size of the output voltage of the AC component; the latter represents the input voltage or load changes abruptly, the voltage returns to normal time required. DC power supply continuous conductivity type and sub-type switch categories. The former by the frequency transformer single-phase or three-phase AC voltage is changed to the appropriate value, and then rectified, filtered to obtain unstable DC power supply, and then the voltage regulator circuit to obtain a stable voltage (or current). This power line is simple, small ripple, mutual interference, but the volume is large, supplies and more inefficient (often less than 40% to 60%). The latter change adjustment element (or switch) off time than to regulate the output voltage to reach regulation. Such small power consumption, efficiency up to 85%, but the drawback is the large ripple, large mutual interference. Therefore, the rapid development since the 1980s. From the work can be divided into: ① controlled rectifier. By changing the thyristor conduction time to adjust the output voltage. ② Chopper. Input DC voltage is unstable, to change the switch circuit off than getting a one-way pulsating DC, and then filtered to obtain a stable DC voltage. ③ transformer type. First by the unstable DC voltage inverter converts high-frequency alternating current, and then by the transformer, rectifier, filter, resulting from new DC output voltage sampling, feedback control of the inverter frequency, to stabilize the output DC voltage.
5.5 temperature sensing circuit
5.5.1 Analysis of temperature detection program
Because ultrasound is also part of the speed of sound, so in the transmission path will be affected by external factors such as temperature, in order to obtain more precise distance between the sensor and the surface, the temperature sensor detects ambient temperature conditions at the time, and converted to the corresponding the ultrasonic velocity using this rate to calculate the distance you can get more accurate distance. So adding a temperature sensor in the whole system to detect the temperature of the prevailing circumstances.
5.5.2 Introduction to digital temperature sensor DS18B20
DS18B20 American DALLAS company launched a single-bus digital temperature chip [8]. He has a unique single bus interface mode, only use one port will be able to achieve two-way communication with the MCU. Digital signal outputs the signal to improve noise immunity and temperature measurement accuracy. His wide operating voltage range (3.0 ~ 5.5 V), you can use an external power supply, can also be used parasitic power mode, that is, when the bus DQ is high, the signal energy to steal DS18B20 supply. He also negative features, power polarity reverse, DS18B20 will not pick the wrong line and burned, but does not work. It can be programmed to achieve the 9 to 12-bit conversion accuracy temperature setting. Setting higher the resolution, the required temperature data conversion time longer, in practical applications to the resolution and conversion time tradeoff.
5.5.3 DS18B20 structure and circuit
DS18B20 with 3 feet T0-92 package, shaped like a transistor, but also 8-pin SOIC package, as well as 6 feet TSOC package. Temperature range of -55 ~ + 125 ℃, in the range of -10 ~ 85 ℃, an accuracy of ± 0.5 ℃. Each DS18B20 chip ROM is stored in a 64-bit ID number: 8 before the product type number, followed by 48 of the device itself is serial number of the last eight in front 56 cyclic redundancy check code. Because of its parasitic power mode power supply can be used. Thus, it can also mount on a bus with multiple DS18B20, multi-point temperature measurement system.