Inverter of 500W with EGS002 module

I have followed the same EGS002 module and EG8010 datasheet schematic of low power frequency transformer for making 500W inverter. Currently I am facing an issue with voltage loss under load condition that is initially when I turn on the Inverter, it starts smooth with 230V 0.5A AC but as I connect the load of 100W its voltage drops to the 110V and starts decreasing gradually. Same issue happening with the drill machine, when I trigger the drill machine voltage starts decreasing. Please help me to resolve this issue, ands feel free to reply if someone faced the same issue previously. Thanks