ups circuit function

hello friends
i disassemble a ups(uninterruptible power supply) which is powered by a 12 v battery, now as you all know.there is many circuits inside a ups like the inverter(h-bridge),the charger, the rectifier and other control and power circuits.
i traced the tracks and found this circuit(ups schematic) which is used to power a microcontroller and other ics and i don't know how it work exactly so i need your help, a brief explanation and a link to a web article will be much appreciated.
i didn't put the values because i thought it is not important since i only want to know how it work.
notes:
1):in the schematic you will find a component labled TR2 which i am suspicious if its is really a transformer so i uploaded its picture
2):i am trying to troublshoot the charger of the ups and after i done some voltage test across some chips i found there is no power and trace the tracks backwards to this circuit where i found that one of the "NPN transistors" is shorted. what else could be the issue since i didn't replace the transistor yet because i don't have it(j13009)