Design of mine intrinsically safe power supply circuit diagram based on STM32

MOS power IC full range

One-piece inductor

Overview:
0 Introduction The intrinsically safe power supply is an important part of intrinsically safe electrical equipment. Due to the mechanization of coal mines, power supply for underground sensors, corner alarms, etc., communication and alarms require power supply equipment. However, based on the complicated underground environment, the requirements for power supply equipment are also very strict. It requires that the internal and outgoing lines of the power supply circuit are safe whether they are in normal operation or in the fault state, and the generated electric spark will not ignite the surrounding environment. An explosive mixture in the middle. The intrinsically safe power supply has two levels of "ia" and "ib". The intrinsically safe power supply described in this article is the commonly used "ia" rating in the well, which means that it can continue to work in the event of a fault and a protective circuit damage.

1 The composition and working principle of the intrinsically safe power supply
1.1 Power supply In the intrinsically safe power supply, the input +Vin and -Vin are 48 V DC power supply. The DC/DC power conversion module (U1) outputs 12 V DC power. U2 is the 7805 voltage regulator module, and the 12 V DC voltage regulator output. The 5 V voltage supplies power to the comparator. In Figure 1, R1 is the first-stage overcurrent protection sampling resistor, R2 is the second-stage overcurrent protection sampling resistor, and the sampling resistor converts the current value into voltage values ​​GND1 and GND2 for overcurrent monitoring using STM32.

Figure 1 Working principle

1.2 Main circuit Since the system is based on the monitoring of the STM32 intrinsically safe power supply, Figure 2 is the main circuit. In the figure, UrU1, UrU2 and UrUrout are the sampling voltages. By monitoring these three voltage values, the STM32 can determine whether the intrinsically safe power supply is overvoltage. . When BH1 is low level, Q4 is not turned on, Q3 is turned off, then the intrinsically safe power supply has no output; when BH1 is high level, Q4 and Q3 are turned on, and Q1 and Q2 are also turned on. Since Q1 and Q2 turn on UrU2, there is a sampling voltage. The level of BH2 determines whether the voltage on R24 is zero. Therefore, only when BH1 and BH2 are at the same time high level, the intrinsically safe power supply has an output, and any one of them is a low level intrinsically safe power supply to enter the protection state, which is the double protection of the main circuit.

Figure 2 main circuit

1.3 Protection circuit The protection circuit in this system has overcurrent protection and overvoltage protection and recovery circuit. This system is an "ia" rated intrinsically safe power supply. All protection circuits have 2 levels. This article only introduces 1 level. The circuits of level 2 and level 1 are identical.
(1) Overcurrent protection The sampling resistor in Figure 1 converts the current value into voltage values ​​GND1 and GND2. In Figure 3, the regulation rheostat R32 sets the overcurrent protection value to 800 mA, and the sampling voltage GND1 is amplified by U3 and then passed through the comparator. U4 compares with the set voltage value to control BH1. When GND1 is greater than the set value, the comparator output is low and the intrinsically safe power supply has no output. At the same time, the amplified GND1 is connected to the AD converter pin of the STM32 via the voltage follower U5 for software monitoring. The second level of overcurrent protection is the same.

Figure 3 Overcurrent protection

(2) Overvoltage protection and its recovery circuit adjustment The varistor R5 in Figure 4 sets the overvoltage protection value to 12.5 V. The output Urout of the intrinsically safe power supply is compared with the set value by the voltage division of R44 and R47 through U7. When the partial pressure value is greater than the set value, the BH1 output is low, and the intrinsically safe power output is zero. When R37 is adjusted so that the output of the intrinsically safe power supply is zero, the voltage at the inverting input of U6 is greater than the voltage at the same input. When Urout=0, D7 and D8 are turned on, and the output of the comparator BH1 is high. Then the intrinsically safe power supply has output. If Urout is still greater than the protection value, U7
Output BH1 is zero, D7, D8 turn on U6 output BH1 is high, and so on until the intrinsically safe power output is within the normal range. The second stage overvoltage protection and its recovery circuit are the same.

Figure 4 Overvoltage protection (please read the PDF for details)