Circuit Design of Buck-Voltage Converter with Digital Control System

The objects of research are processes in electrical scheme and enormous digital control systems in converter. One of the most problematic things is transfer and energy change in converter for current and voltage in order to reach certain value of digital range with a minimal percentage of error.<br><br>This work explores buck-voltage converter with digital control system. An enormous considered procedure of projecting electrical scheme. There was described electrical scheme with a control system, which, thanks to the digital system, provides dates with more accuracy in the output of converter, among them: assignment of certain digital range of output voltage and system’s impact on working scheme.<br><br>During the research there was used selection of hardware features and software tools, accepting peripheral devices, which let quickly and simply set up microcontroller for certain operating mode and to realize controlling system for buck converter in a programmatic manner.<br><br>There was analyzed procedure of solving and choosing of the certain parts of electrical scheme, where was used to construct:<br><br>– microcontroller for receiving, processing and issuance of information in electrical scheme;<br><br>– driver operating and analog-to-digital conversion;<br><br>– driver for control of the switches – basically transistors;<br><br>– components of the buck-converter circuit.<br><br>There is description and schematic choice of the certain parts of the scheme. There was included switch, capacitor and diode for buck converter; certain range of the frequency and voltage for microcontroller; control of the power keys of the circuit with the corresponding operating parameters for driver.<br><br>There was received a system, which in prospect will become a basis to step down voltage value to the certain level. This is because defined method has a set of features, particularly digital regulation system with a discrete step and analog-to-digital converter in the capacity of feedback. Therewith provides possibility for receiving more accuracy value. In comparison with analogic buck converters, this converter has voltage parameter with fractional error.


Introduction
There is often happens situation, in which voltage value of the internal source can be low or big for reliable working process. For example, in order wireless charging systems could transfer voltage in range of 5-7 volts for certain devices or 70-80 volts for certain autos. Actually, voltage value could be not enough or more level, than it is necessary. In order to solve this problem it is possible to use electrical filters and additional resistors with other components. The problems of it are great volume and big weight, exploitation conditions for connection system comes wrong. Therefore, it is efficiently to use buck-converter in order to receive certain value. Analogic researches were made in [1] for boost-voltage converter with digital system control and in [2] for buck-boost converter with voltage feedback control. Therefore, the objects of research are processes in electrical scheme and enormous digital control systems in converter. The aim of the article is projecting, researching and practical realization of semiconducting voltage buck converter with digital system control.

Methods of research
2.1. Calculation of parameters in buck converter scheme. There is in Fig. 1 an electrical principle scheme of the buck voltage converter. Power circuit of converter has transistor VT 1 . If the key switched on, output current, which flows through the inductance coil ( ), L rises. Inductance coil is coupling magnetic field energy. If the key switched off, coupled electrical energy in the inductance coil will be send to the capacitor ( ) C and load ( ). R L Bypass diode ( ) VD 1 lets the pass for the current to flow. In order to realize the scheme it is important to calculate nominals of the elements in the buck converter [3,4].

ISSN 2664-9969
Calculation would be finished with a certain parameters: maximal output current I out .max . , = 0 46 A frequency switching f sw = 10 kHz, inductive current ripple factor LIR = 0 3 . , range of input voltage U in = − 7 24 V and output voltage U out = 5 V. Inductance calculation is an important moment during converter projecting, insofar as there is dependence on values of maximal input U in.max and output U out voltage: where f sw -frequency switching transistor; LIR -inductive current ripple factor; I out .max -maximal value of output current. Peak current of the inductance coil I peak solves as: Output capacitor with a maximum available amplitude swing of ripples of the output voltage ΔU (accept ΔU =100 mV): . .
Capacitance of the input capacitor, including of the load current I L and swing of ripples of the output voltage U out ripple . : .14 10 Hz 40 mV 183 uF. 4 Duty cycle of the open state power key relative period of the pulse width modulation: 2.2. Choice of microcontroller in electrical scheme. It was selected integral scheme PIC16F877A as microcontroller in Fig. 2 [5,6]. This scheme is very convenient for a work, coding of this controller is not so difficult. One of the main advantages is that it can be write-erase as many times as possible because it uses FLASH memory technology. It has a total number of 40 pins and there are 33 pins for input and output. PIC16F877A finds its applications in a huge number of devices. It is used in security, remote sensors and safety devices, home automation and many industrial instruments. An enormous EEPROM is also featured in it which makes it possible to store some of the information permanently like transmitter codes and receiver frequencies and some other related data. The cost of this controller is not expensive and its handling is also easy. It is flexible and can be used in areas where microcontrollers have never been used before as in microprocessor applications and timer functions etc. It works in a range until 20 MHz and in a range of voltage 4.2-5.5 V.
2.3. Choice of the driver in electrical scheme. It was selected IR2184S as driver in Fig. 3, as it is driver MOSFET of the high voltage in the integrated scheme [7][8][9]. It can control by the keys in the half-bridge and bridge schemes of the low resistance both with high and low level. Schemes of the drivers are using MOSFET with high and low level.
Gate drive supply range from 10 to 20 V, output source capability is equal to 1 4 . A and sink current capability is equal to 1. As a basis, there was taken [10]. With this set of bundled hardware and software, it is quite quick and easy to set up the microcontroller to the certain operating mode and to implement the buck converter control programmatically.
In order to provide galvanic isolation of the power circuit and controlling system, transmission impulse of controlling was made with the using of the half-bridge driver IR2184S.
3.2. The results of the experiment. Electric principle scheme in Fig. 4 was projected and modulated in the programmed application Proteus, which model represented.
In Fig. 5 there is a general form of buck converter realization in program. In Fig. 6 there is represented realization of the model of buck converter with a digital controlling system in programmed application Proteus that relates to the electrical principle scheme in Fig. 4. Fig. 7 is represented researching of the graphics of projected buck converter with a defined voltage of input voltage 12 V and output voltage -5 V. In order to support constant output voltage, regulator changes porosity of the controlling signal. An enormous, in Fig. 7, a demonstrated signal of the pulse width modulation (PWM) that flows to MOSFET transistor IRF540 and output voltage in Fig. 7, b. All over the elements are playing a main role in the converter. To be sure, there was considered capability of the scheme to work without capacitor C out . It is obviously, that output capacitor rectify voltage and the voltage is rippling in output of converter.

Conclusions
There was developed principle of the technical realization of the semiconducting buck voltage converter. It can be used in a lot of devices. There was analyzed capability to create power supply equipment based on PWM for the input voltage of the discrete current. There also was researched that for practical realization of the buck voltage converter, which was based on inductive-capacitive converter, it is conveniently using of the digital system controlling. According to the certain graphics in Fig. 7, a and Fig. 7, b, scheme was successfully tested.