I want to use the step down transformer to step down the 220V ac to 15V ac. Then, pass it into the bridge rectifier. Then, use 7812 to stablize the 15V ac to 12V dc, connect the 7809 to stablized 12V dc to stablize the output to 9V dc, again, connect the 7805 to stablized 9V dc to stablize the output to 5V dc. Is it right to do it? In addition, can anyone tell me what values of filter capacitors should I use in this circuit? Actually, can anyone tell me how to calculate these values? I know that it is related the time constant (R x C), right? Please help me!