Design Scheme of Switching Stabilized Power Supply Using MSP430 Single Chip Computer

“This switching power supply is based on MSP430F449 as the main control device. It is a powerful single-chip microcomputer with 16-bit ultra-low power consumption characteristics produced by TI. Its low power consumption is conducive to the requirements of high system efficiency, and its ADC12 is The high-precision 12-bit A/D conversion module has 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.

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

System structure and overall design plan

This switching power supply is based on MSP430F449 as the main control device. It is a powerful single-chip microcomputer with 16-bit ultra-low power consumption characteristics produced by TI. Its low power consumption is conducive to the requirements of high system efficiency, and its ADC12 is The high-precision 12-bit A/D conversion module has 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 as in Fig. 1.

Hardware circuit design

1 DC/ DC conversion circuit design

The main hardware circuit of the system is composed of power supply part, rectifier filter circuit, DC/DC conversion circuit, drive circuit, MSP430 single-chip microcomputer and other parts. The AC input voltage passes through the DC/DC converter after the rectifier filter circuit, 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 accumulated by the Inductor L in one cycle is equal to the energy released, namely:

In formula (1), I1 is the output current, and the current through the inductance energy storage is related to the inductance value. In the actual circuit, the parameters of the inductance and the selection of the switching frequency and input/output voltage requirements, select the appropriate inductance value according to the requirements of the actual circuit, and pay attention to its internal resistance should not be too large, so as to avoid excessive loss and reduce efficiency sampling Circuit. For the calculation of capacitance, under the specified ripple voltage limit, the selection of its size is mainly 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.

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 the sampling channels of the MSP430 chip, P6.0 is the voltage acquisition, and P6.1 is the current acquisition.

Voltage acquisition Because the sampling signal needs to be input into the MCU MSP430, its internal sampling reference voltage is selected as 2.5 V, so the input sampling voltage should be limited to 2.5 V, and the input voltage should be limited to 2 V in consideration of the safety margin. When the input voltage is 36 V, the sampling voltage is: 12/(12+200)×36=2.04 V, which meets the requirements.

Constantan wire is used for current collection. First consider the efficiency issue. Constantan wire cannot be selected too large. At the same time, the reference voltage of MSP430 is 2.5 V, and the required constantan wire needs to be self-made. Considering the above aspects, the resistance value of the constantan wire is about 0.1 Ω.

3 Design of PWM drive circuit

The power MOSFET drive power is small, and the triode drive can meet the requirements. The drive circuit is shown in Figure 4.

Because the single chip microcomputer is a weak current system, it needs to be isolated from the strong current side in order to ensure safety to prevent voltage backflow on the strong current side and burn out the MSP430. First, use the switch optocoupler for photoelectric isolation, and then pass the Transistor to the MOSFET drive circuit IR2101. The PWM wave generated by MSP430 passes through the optocoupler and the IR2101 chip behind, and the PWM wave output on the 5-pin of the chip is connected to the gate G of the MOSFET to make it work. IR2101 is specially used to drive N-channel mosfets and IGBTs that can withstand high voltage and high frequency. It is an 8-pin chip with high and low side output reference levels. The voltage range provided by the gate is 10 to 20 V.

4 Design of protection circuit

Overcurrent protection is a power supply load protection function to avoid damage to the power supply and load caused by overload output current including a 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 MSP430 single-chip microcomputer is used to control the normally open and normally closed pull-in of the relay to realize the function of automatically recovering the circuit work. As shown in Figure 5:

software design

The MSP430 microcontroller has multiple clock sources with high, medium and low speeds, which can be flexibly configured for each module and work in a variety of low-power modes, greatly reducing the power consumption of the control circuit and improving the overall efficiency; 430F449 has ADC12 module that can achieve 12 Bit-precision analog-to-digital conversion, hardware multiplier, and TIMERA and TIMRB timers with PWM output function enable the entire circuit to complete real-time acquisition of power supply output voltage and current, PI control, and PWM output without any expansion; at the same time MSP430F449 has an internal LCD drive module, which can directly connect the LCD display to the drive port of the chip, and the circuit structure is extremely simple. The software of this design is written in C language. The whole program includes sub-modules: keyboard control module, A/D voltage and current acquisition module, PI control module and PWM wave generation module. The software flow chart is shown in Figure 6. Show.

Keyboard control and display module: The voltage reference value can be set through the keyboard, and the voltage and current can be switched and displayed. The setting and display of reference voltage are realized through LED, and the collected values ​​of voltage and current are displayed through LCD.

AD voltage and current acquisition module: Through the 12-bit A/D conversion module of MSP430 single-chip microcomputer, the voltage value and load current output by the system are collected.

PI control module: This module is used to control the output voltage of the system to stabilize the output voltage. Its control principle is shown as in Fig. 7.

PWM wave generation module: Use the comparison function of the TimerB timer of the MSP430 microcontroller to generate a signal to drive the MOSFET.

Analysis of results

Through the single-chip MSP430 software design, reasonable parameters and switching frequency are selected for PI adjustment, which can achieve the effect of voltage stabilization, so that the first three indicators above can achieve good results. Whether the ripple voltage can be limited is mainly due to the Capacitors in the rectifier filter circuit. Therefore, the selection of high withstand voltage supporting electrolytic capacitors is important.

After selecting the switching element, the efficiency is mainly affected by the switching frequency, the internal resistance of the energy storage inductor, and the loss of other devices in the line. Therefore, the level of loss should be paid attention to in the selection of the device. Carry on the comprehensive test to this system, the result is shown in Table 1.

This switching power supply design adopts the smallest system board of TI’s 16-bit single-chip MSP430F449 chip machine with low power consumption as the control core, and is based on PWM control technology, closed-loop PI adjustment, and high-precision 12-bit A/D conversion. The function and parameter index of sampling value display and setting voltage value. The experimental results show that: through the single-chip MSP430 software design, reasonable parameters and switching frequency are selected for PI adjustment, and the effect of voltage stabilization can be achieved.