The distributed battery management system of electric vehicles mostly uses a master control unit and several slave control units. Unlike most electric vehicle battery management systems that use a 12V battery for power supply, the BMS discussed in this article is directly powered by the power battery pack (total voltage of 72V). This not only saves the purchase cost of a 12V battery but also reduces the battery charging work during the vehicle’s operation. However, to use such a high battery pack voltage to power the BMS master control unit, which only requires a 5V power supply, a matching voltage conversion circuit must be designed.

This article selects the LM5017 produced by Texas Instruments as the primary power conversion chip. This chip is a highly integrated and versatile DC/DC power chip with a wide input voltage range of 7.5V to 100V, output current up to 0.6A, and an output voltage range of 1.25V to 90V (flexibly adjustable based on the peripheral circuit). This article is configured for a standard 10V output. However, considering that the terminal voltage of the power battery pack may fluctuate during the operation of high-speed electric vehicles, causing the output voltage of the LM5017 to fluctuate as well, a LM7805 three-terminal voltage regulator is configured after the LM5017. This regulator can reduce the DC voltage from 7.5V to 20V to a stable +5V output. The circuit diagram of the designed master control unit power module is shown in Figure 1.

Figure 1: Circuit of the Master Control Unit Power Module

After completing the circuit design, a PCB was printed and the corresponding components were soldered. During the experimental process, the AC-DC power converter was adjusted multiple times to output a DC voltage of 72V to 90V to power this module, while a multimeter was used to separately detect the +12V and +5V output terminals. The detection process and results are shown in Figure 2. The results prove that this power conversion module can stably output the +12V and +5V voltages required by the electronic devices on high-speed electric vehicles, meeting the requirements for electric vehicle use.

Figure 2: Testing and Debugging of the Master Control Unit Circuit

In the design approach and process of this circuit, in order to prevent the entire circuit board from experiencing overcurrent, short circuit, and other dangerous situations, a plug-in self-resetting fuse was placed at the power input end, with a maximum DC voltage of 90V, holding current of 500mA, and action current of 1A. At the same time, a double-pole double-throw switch S1 and a double-hole connector CON2 were added after the voltage output end of the LM5017, allowing for easy and convenient completion of system software and hardware debugging in the laboratory after the hardware circuit board is made. Additionally, in the 5V circuit output from the LM7805 voltage regulator, a light-emitting diode D1 was added to visually indicate whether the power module is supplying power normally, and an additional double-hole connector CON3 was placed to provide a 5V working voltage for the peripheral circuit being built for future system upgrades.

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