Bus technology commonly used in the hottest power

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Bus technology commonly used in power supply

1 preface

with the penetration of IT technology into power supply technology, digital power supply technology came into being. Due to a series of advantages of digital power supply, such as flexible control, flexible structural changes, convenient adjustment, maintenance and low cost, it represents the development direction of power supply technology. In digital power supply, bus technology plays a very important role. This paper introduces the common bus technology in digital power supply

2 I2C bus

i2c bus is the abbreviation of English inter integrated circuit bus, which is often translated as inter integrated circuit bus or internal integrated circuit bus. I2C bus is recognized by manufacturers for its powerful control ability and exquisite circuit structure. At present, I2C bus has been widely used in many electronic products

The relevant technical indexes of I2C bus interface were first determined in 1982. Philips first introduced the I2C bus in the form of a simple two-wire interface, which is used to realize the value of 2 between the relevant electronic components in the same circuit board or cabinet (an electronic extensometer needs to be equipped additionally) and can also display the force elongation curve (an encoder needs to be equipped additionally) communication. In 1987, Philips owned the patent of I2C bus. There are two signal lines in I2C, one for clock signal transmission and one for data signal transmission. Through I2C bus, relevant commands, control and working information can be completed between master control components and slave control components, and transmitted through two serial signal lines. The most typical application of I2C bus is to complete the communication control between related components through a master control component. Due to the simplicity of using I2C bus, I2C bus has been widely used at present. The relevant performance of I2C bus has been continuously improved, and the communication rate and addressing range have also been continuously improved

as an industrial standard, I2C bus is an attractive physical communication mode. In the acces bus, SM bus, psmi and IPMI industrial standard buses, the relevant technical indicators of I2C bus are also cited. I2C bus can be applied to many microcontrollers, and in many applications, I2C bus can also be driven by software using general i/o pins. For example, in 1991, some companies took the lead in the development of access bus (access bus, referred to as A.B). Here, I2C bus is used as its physical communication layer, so that access bus has the ability to enable the controlled devices. Access bus is used as an improved, simplified, standardized and flexible multi-purpose method to connect the internal and external devices of the computer to the CPU. It supports the work of devices such as clock and battery power monitoring, It also supports keyboard, mouse, monitor and modem. In 1995, the access bus working group (abig) released the version of V3.0 technical documents, and some companies (such as USAR and Fujitsu of Japan participated in abig activities. In 2011, they actively participated in the smart battery system interface Forum: sbs-if)

2.1 about I2C bus

i2c bus is a serial bus system. I2C bus is composed of two lines, one is a serial data line, which is commonly represented by SDA; The other is a serial clock line, which is usually represented by SCL. CPU uses serial clock line to send clock signal and serial data line to send or receive data to realize the adjustment and control of the controlled circuit. Since I2C bus has only two signal lines, the data transmission mode is serial mode, and its data transmission speed is lower than that of parallel data transmission mode. However, I2C bus occupies only two pins of CPU, which is conducive to simplifying the peripheral circuit of CPU

in I2C bus system, CPU is the core, I2C bus is led out by CPU circuit, and other controlled objects are connected to I2C bus. The circuit structure diagram of I2C bus system is shown in Figure 1

Figure 1 Schematic diagram of I2C bus system circuit structure

2.2 I2C bus interface circuit

i2c bus transmits digital signals. If the controlled integrated circuit connected to the I2C bus is an analog circuit, in order to facilitate communication with the controlled analog circuit, I2C bus interface circuit needs to be added to the controlled object. The working principle diagram of I2C bus interface circuit in the controlled IC is shown in Figure 2. The interface circuit is generally composed of I2C controller, control switch and other circuits. Only after the data information sent by the CPU is decoded by the decoder can the control signal perform the control operation on the controlled IC. The controlled object receives the control instructions and data sent by the CPU through the I2C bus interface circuit to realize the control of the controlled object by the CPU

i2c bus is a bidirectional bus system. Through I2C bus, CPU can send data to the controlled IC, and the controlled IC can also transmit data to CPU through I2C bus, but whether the controlled IC receives data or sends data is controlled by CPU. Since I2C bus is a bidirectional bus system, CPU can check the fault of relevant circuits connected to I2C bus

for the electrical appliances with automatic production adjustment function, the computer on the production line can be connected to the I2C bus of the electrical appliances. According to the preset functions and requirements of different adjustment items of the electrical appliances, the best adjustment data can be transferred to the E2PROM memory of the electrical appliances, and the standard data can also be solidified in the read-only memory of the CPU. The appliance adopting I2C bus saves a lot of adjustable potentiometers, simplifies the adjustment process, has good product consistency and high working reliability

Figure 2 Schematic diagram of circuit structure of I2C bus system

2.3 functions of I2C bus system

I2C bus system with CPU as the core is mainly used to complete the following functions

⑴ user operation function

when users use electrical appliances, they usually need to adjust and control relevant control parameters. During operation, they only need to press the corresponding keys on the local keyboard or remote control keyboard, and the CPU will send relevant control instructions to the controlled circuit through I2C bus

⑵ maintenance and adjustment function

complete the control function of setting and adjusting the working mode of each unit circuit of the controlled appliance. In ordinary electrical appliances, adjustable potentiometers are used to adjust various working parameters of relevant unit circuits. In the controlled appliance of I2C bus, these parameters can be specially adjusted by the operator, and then the relevant working parameters can be adjusted through the remote control or local operation keys. ⑶ fault self-test function

since the information on the I2C bus is transmitted Bi directionally by the SDA and SCL serial data signal lines, the CPU can monitor the communication of the I2C bus and the working state of the controlled integrated circuit, and display the detection results on the screen to provide maintenance personnel with relevant fault self-test information. When the low-level response signal is sent by the controlled device, the CPU will judge that the controlled device is faulty and terminate the data transmission. Because each controlled integrated circuit and device has its own address, so many control signals are transmitted on the bus at different times, but as long as each controlled device takes the control signal with the same address from the bus, identifies and processes it, and obtains the corresponding control signal, it can realize the corresponding control

2.4 control process of I2C bus system

⑴ data exchange between CPU and memory

the memory in I2C bus system stores two kinds of information: one is user information, which is the control information written by the user. This information can be changed by the user, such as various analog control quantities (such as OVP, OCP, OTP of power supply and the required output voltage value); The other is the control information, which is the control data written by the manufacturer and cannot be changed by the user. When the appliance works normally, the CPU takes out the relevant user information and control information from the memory and sends them to the controlled circuit to make it work normally; When adjusting the electrical appliance, the CPU also takes out the control information from the memory, and the maintenance personnel use the correct debugging steps to change these control information to ensure that the electrical appliance using I2C bus is in the best working state

⑵ the control process of CPU on the controlled electrical appliances

cpu on the controlled electrical appliances using I2C bus needs to go through the following process

① CPU addressing process. When the CPU wants to control a controlled device, the CPU will send the address instruction of the controlled device to the bus. After receiving the instruction, the controlled device will send response information. After receiving the response information, the CPU bus will take the controlled device as the control object

② CPU calls data process. After finding the controlled device, the CPU calls out the corresponding user information and control information from the memory and sends them to the controlled device through I2C bus, so that the controlled device is in the required working state

③ the process of the controlled device executing instructions. After receiving the instruction, the controlled device decodes the instruction, and compares the decoding result with its own control content coding to determine what operation to carry out. This work is completed by the decoder in the bus interface circuit. After determining what kind of operation to carry out, the corresponding control switch in the bus interface circuit will be automatically turned on, and the control data will be sent to the d/a converter through the control switch and converted into analog control voltage to control the corresponding analog circuit and complete the relevant operations. The busiest time of I2C bus data transmission is the moment when I2C bus circuit is used. Because the controlled circuit has no function of storing data, the CPU should take out the control data from the memory and send it to each controlled device every time it is powered on, so that the controlled device can enter the corresponding working state. Therefore, when the CPU is just started, the control task is the heaviest, the control process is the most complex, and the possibility of damage is the greatest. Therefore, electrical appliances using I2C bus should try to avoid frequent startup/shutdown

according to the strength of electrical functions and the different controlled circuits connected to the I2C bus, one or more groups of I2C buses can be led out on the CPU used by the I2C bus

integrated circuits or devices controlled by I2C bus must have special bus terminals, namely SDA terminal and SCL terminal. All integrated circuits or devices with SDA and SCL terminals (pins) can be controlled by the bus

2.5 transmission mode of I2C bus signal

the two signal lines (SDA, SCL) in I2C bus have strict division of labor in the process of transmitting various control signals. Among them, SDA data line is used to transmit the data of each control signal and the address occupied by these data; SCL clock line is used to measure the working beat between the controller and the controlled device. In order to ensure the power supply of the bus output circuit, SDA line and SCL line are connected with the power supply through the pull-up resistor. When the bus is idle, SDA and SCL lines maintain high level. The transmission waveform of I2C bus control signal is shown in Figure 3

Figure 3. I2C bus control signal transmission waveform

(1) during the period when the clock line control signal

scl line is at high level, the data transmitted on SDA line must remain stable. During this period, data can be exchanged between the controller and the controlled device; When the SCL line is at low level, the data transmitted on the SDA line can change, that is, it is allowed to jump between high and low levels on the data line

(2) data line control signal

the control signals transmitted on the data line are transmitted successively according to the content and sequence shown in Figure 3: starting state signal, controlled circuit address, reading and writing mode (data transmission direction bit), response signal, data signal, response signal, data signal, response signal, termination state signal

when the clock line is at high level, a level jump on the data line from high to low is specified as the starting state, and the level jump from low to high is specified as the ending state. Both the starting state signal and the ending state signal are sent by the CPU. When CPU sends

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