bbkv_tom
Newbie level 4
I have a stepdown transformer that converts 230VAC to 9VAC..9VAC is given to a bridge rectifier(1V drop across) and then to an LDO(0.5V drop across) that converts to 5VDC..i need to draw a maximum current of 100mA(worst case) from the 5VDC for my board operation..Few clarification i need is
1) I'm using a 1.5VA transformer ie 9VAC, 166mA secondary rating..IF i need to draw a max of 100mA out of the regulator output after rectifying using a bridge rectifier of 1V drop..Even if the drop across bridge and LDO is added there is enough voltage at regulator input..Is this calculation right..Am i missing something
2) What should be the value of bulk cap i need to provide after the bridge rectifier.what is the formula for calculating that?
3)At the 230VAc input to transformer i have provided an MOV of 700V clamping volatage and 2500A surge current protection..do i need to provide a series resistor and a fuse also in the Mains input? Is resettable fuse OK to be used at the input..i cannot use a blow type fuse since the components on the board is not so easy to access when it is assembled inside the enclosure
Please provide your suggestions..
Thanks
1) I'm using a 1.5VA transformer ie 9VAC, 166mA secondary rating..IF i need to draw a max of 100mA out of the regulator output after rectifying using a bridge rectifier of 1V drop..Even if the drop across bridge and LDO is added there is enough voltage at regulator input..Is this calculation right..Am i missing something
2) What should be the value of bulk cap i need to provide after the bridge rectifier.what is the formula for calculating that?
3)At the 230VAc input to transformer i have provided an MOV of 700V clamping volatage and 2500A surge current protection..do i need to provide a series resistor and a fuse also in the Mains input? Is resettable fuse OK to be used at the input..i cannot use a blow type fuse since the components on the board is not so easy to access when it is assembled inside the enclosure
Please provide your suggestions..
Thanks