In this submission we try to investigate the low battery and the overload protection stages as designed for the proposed sinewave UPS circuit using PIC16F72.
Data provided by: Mr. hisham bahaa-aldeen (firstname.lastname@example.org)
LOW BATTERY PROTECTION:
While the controller operates in the inverter-mode it repeatedly monitors the voltage at its pin4 (BATT SENSE), pin7 (OVER LOAD sense) and pin2 (AC MAIN sense).
Should the voltage at pin4 rise above 2.6V the controller would take no notice of it and may be seen escaping to supplementary sensing-mode, but as soon as the voltage here drops to around 2.5V the controller stage would prohibit its functioning at this point, switching OFF the inverter-mode such that the low battery LED turns ON and prompting the buzzer to beep.
Over load protection is a mandatory functionality implemented in most inverter systems. Up here, in order to cut-of the inverter in the event the load goes beyond the safe load specifications, the battery current is first detected across the negative line (i.e the voltage drop across the fuse and negative path of the low side MOSFET bank) and this greatly reduced voltage (in mV) is proportionately intensified by the comparator U5 (composing of pins12,13 1nd 14) (make reference to circuit diagram).
This amplified voltage output from pin14 of comparator (U5) is rigged as inverting amplifier and applied to pin7 of the microcontroller.
The software compares the voltage with the reference, which is for this particular pin is 2V. Quite as talked over previously the controller senses the voltages in this pin besides operating the system in the inverter-mode, every time the load current augments the voltage at this pin builds up, whenever the voltage on pin7 of the controller IC is above 2V the process shuts off the inverter and switches to overload mode, shutting off the inverter, turning ON the overload LED and causing the buzzer to beep, which after 9-beeps prompts the inverter to switched-ON again, inspecting the voltage at pin7 for a second time, suppose in case the controller identifies pin7 voltage to be below 2V, it then operates the inverter on normal mode, other wise it disconnects the inverter yet again, and this process is known as the auto-reset-mode.
Like in this article we articulated beforehand that when in inverter-mode, the controller reads the voltage at its pin4 (for Low-batt), pin7 (for overload) and pin2 for AC main voltage status. We comprehend that the system may be functioning in twin mode (a) UPS mode,(b) inverter mode.
So before inspecting the pin2 voltage of PIC the routine before anything else confirms at what mode the unit may be working by sensing the high/lo logic at pin16 of the PIC.
Inverter to mains changeover (INV-MODE):
In this particular mode as soon as the AC main voltage is detected to be in the vicinity of 140V AC, the changeover action can be seen implemented, this voltage threshold is pre-settable by the user, implies that in cases where the pin2 voltage is above 0.9V, the controller IC may shut off the inverter and switch to mains-on mode, where the system examines the pin2 voltage to test the AC mains failure and maintain the charging process, which in this article we will be explaining later on.
Inverter to Battery changeover (UPS-MODE):
Within this setting each time the AC main voltage is in the vicinity of 190V AC the changeover may be seen enforcing to battery mode, this voltage threshold is also software pre-setteble, meaning when ever the pin2 volage is above 1.22V the controller may be expected to switch ON the inverter and switched to battery routine wherein the system inspects the pin2 voltage to verifies the AC mains absence and operates the charging schedule which we would be discussing further down in the article.