Application of MSP430 microcontroller in power supply control

MSP430 series MCU is a new generation of 16-bit MCU produced by TI in the United States. It is an ultra-low power mixed signal processor (MixedSignal Processor ). It has the advantages of low voltage, ultra-low power consumption, powerful processing capability, stable system operation, rich on-chip peripherals, convenient development, etc. It has a high cost performance and has an extremely wide range of applications in engineering control and other fields. The switching Boost voltage-stabilized power supply uses the energy storage characteristics of switching device control, passive magnetic components and capacitor components to obtain separated energy from the input voltage source, temporarily store the energy in the form of a magnetic field in the inductor, or in the form of an electric field in the capacitor, and then convert the energy to the load. The Boost boost chopper circuit is used for the DC-DC main circuit.

2 System structure and overall design

This switching voltage regulator is based on MSP430F449 as the main control device. It is a powerful 16-bit ultra-low power microcontroller produced by TI. Its low power consumption is conducive to the high efficiency of the system, and its ADC l2 is a high-precision 12-bit A/D conversion module with high speed and universal characteristics. Here, MSP430 is used to complete the PI adjustment of voltage feedback; PWM wave generation, reference voltage setting; voltage and current display; over-current protection, etc.

The system block diagram is shown in Figure 1.

3 Hardware Circuit Design

3.1 DC/DC conversion circuit design

The main hardware circuit of the system consists of power supply, rectifier and filter circuit, DC/DC conversion circuit, drive circuit, MSP430 microcontroller, etc. After the AC input voltage passes through the rectifier and filter circuit, it passes through the DC/DC converter and adopts the Boost boost chopper circuit for DC/DC conversion, as shown in Figure 2:

According to the working principle of the boost chopper circuit, the energy stored in the inductor L is equal to the energy released in one cycle, that is:

In formula (1), I1 is the output current. The current through which the inductor stores energy is related to the inductance value. In the actual circuit, the parameters of the inductor are related to the selected switching frequency and input/output voltage requirements. According to the requirements of the actual circuit, the appropriate inductance value should be selected, and it should be noted that its internal resistance should not be too large, so as to avoid excessive loss and reduce the efficiency of the sampling circuit. For the calculation of the capacitor, under the specified ripple voltage limit, its size is mainly selected based on formula (2):

In formula (2), C is the value of the capacitor; D1 is the duty cycle; TS is the switching period of the MOSFET; I0 is the load current; V' is the output voltage ripple.

3.2 Sampling Circuit

The sampling circuit is a voltage acquisition and current acquisition circuit, and the sampling circuit is shown in Figure 3. Among them, P6.0 and P6.1 are sampling channels of the MSP430 chip, P6.0 is for voltage acquisition, and P6.1 is for current acquisition.

For voltage acquisition, because the sampling signal needs to be input into the MSP430 microcontroller, its internal sampling reference voltage is selected as 2.5 V. Therefore, the input sampling voltage must be limited to below 2.5 V. Considering the safety margin, the input voltage is limited to below 2 V. When the input voltage is 36 V, the sampling voltage is: 12/(12+200)×36=2.04 V, which meets the requirements.

The current is collected using constantan wire. First of all, considering the efficiency, the constantan wire cannot be too large. At the same time, the reference voltage of MSP430 is 2.5 V, and the required constantan wire must be homemade. Considering the above aspects, the resistance value of the constantan wire is about 0.1Ω.

3.3 Design of PWM drive circuit

The driving power of the power MOSFET is small, and the requirement can be met by using a transistor drive. The driving circuit is shown in Figure 4.

Since the single-chip microcomputer is a weak current system, it needs to be isolated from the strong current side to ensure safety, to prevent the voltage on the strong current side from flowing back and burning the MSP430. First, use a switch optocoupler for photoelectric isolation, and then pass through the transistor to the MOSFET drive circuit IR2101. The PWM wave generated by the MSP430 passes through the optocoupler and the IR2101 chip behind it. The PWM wave output at the 5-pin of the chip is connected to the gate G end of the MOS-FET to make it work. IR2101 is specially used to drive N-channel MOSFET and IGBT with high voltage and high frequency resistance. It is an 8-pin chip with high and low side output reference levels. The voltage range provided by the gate is 10-20 V.

3.4 Design of protection circuit

Overcurrent protection is a power supply load protection function to prevent damage to the power supply and load caused by overload output current, including short circuit on the output terminal. When the current is greater than the limit value, the normally closed contact of the relay is disconnected for protection. The normally open and normally closed contact of the relay is controlled by the MSP430 microcontroller to realize the function of automatically restoring the circuit operation. As shown in Figure 5: