RESEARCH OF A MICROCONTROLLER CHARGER FOR LITHIUM BATTERIES

Abstract

Lithium battery chargers work on the principle of limiting the charge voltage. Among the features of such a charge, the following parameters are distinguished, such as a 3—4 times increase in the voltage of the lithium battery cell, smaller allowable deviations of the charge voltage (linearity of the current-voltage characteristic) and the absence of the need for a compensatory charge (jet recharging) after the battery reaches a state of full charge . Let's consider the specifics of the charge on the example of portable lithium batteries with an output voltage of 4.2 V, the specifics of the charge of which (and with a higher output voltage) consists in the use of the CC-CV method.
 To simulate the operation of the charger and debug the MK program, an electrical schematic diagram was compiled in the ISIS Proteus environment. To test this circuit, the model includes an STM32F103 MC, which is used to generate a PWM signal whose frequency is 62 kHz. Next, the output current is measured, with a setting of the PWM signal strength within 50 %. According to the indicators at the output of the operational amplifier in the current measurement mode, it is possible to determine the current in the ammeter battery circuit.
 Based on the simulation results of the developed scheme and algorithm, it can be concluded that this scheme ensures the fulfillment of the necessary modes of operation of the investigated charging device and is suitable for further implementation. A 32-bit MC of the STM32F103C8 series, located on the BluePill platform — a development board for the ARM Cortex M3 microcontroller, was selected as the control element of the control unit. The stable operating mode of the MK is ensured by two crystal oscillators of 8 MHz and 32768 Hz, and using the built-in frequency multiplier, the MK provides support for the operating frequency equal to 72 MHz.
 As a result, the functionality of the charger circuit and the SS-СV algorithm for fast charging of lithium batteries was developed and confirmed. The use of the CC-CV charge method made it possible to increase the output current of the charge, as well as reduce the time required to restore the energy properties of the battery, while current fluctuations are reduced by 96 %, compared to schemes that use only constant voltage methods.