In this page we learn specifically about the battery charging operations using PWM technique as configured for the proposed sinewave UPS circuit using PIC16F72.
Data provided by: Mr. hisham bahaa-aldeen (firstname.lastname@example.org)
In the course of MAINs ON Battery charging may be seen initiated. As we may understand while in battery charging mode the system may be functioning using the SMPS technique, let us now understand the working principle behind it.
To charge the battery the output circuit (MOSFET and Inverter transformer) becomes effective in the form of a boost converter.
In this case all the low side MOSFETs of the two the mosfet arrays work in sync as a switching stage while the primary of the inverter transformer behave as an inductor.
As soon as all of the low side MOSFETs are switched-ON the electric power gets accumulated in the primary section of transformer, and as soon as the MOSFETs are OFF this accumulated electric power is rectified by the in-build diode inside the MOSFETs and the DC is kicked back to battery pack, the measure of this boosted voltage would depend on the ON-time of the low side MOSFETs or simply mark/space ratio of the duty cycle used for the charging process.
While the equipment may be conducting in the mains-on mode, the charging PWM (from pin13 of micro) is progressively augmented from 1% to highest specification, in case the PWM raises the DC voltage to the battery, the battery voltage too increases which results in a surge in the battery charging current.
The battery charging current is monitored across the DC fuse and negative rail of the PCB and the voltage is additionally intensified by the amplifier U5 (pin8, ppin9 and pin10 of the comparator) this amplified voltage or detected current are applied to the pin5 of microcontroller.
This pin voltage is scheduled in software in the form of 1V, as soon as the voltage in this pin is rises above 1V the controller may be seen restricting the PWM duty cycle until finally it's pulled down to below 1V, assuming the voltage on this pin is decreased to below 1V the controller would instantly begin improving the full PWM output, and the process may be expected to go on in this manner with the controller upholding the voltage on this pin at 1V and consequently the charging current limit.