I got a circuit board from an emergency light when i saw it's circuit it's not common there is a ceramic capacitor and a 330 ohms resistor in its and it give 5.0 volts at the end i don''t know how it's designed but it's giving 5.0 volts at the other end with no transformers ! then i configured the circuit myself as shown in the given diagram but it's giving 180 volts dc instead of 5 volts so my question is : is there anybody who can tell me whats missing in this circuit so its can also give 5volts output?

active| newest | oldestThe other way is to just use OHMS LAW. We know R1 has 215 volts across it... and we know the value of R1 is 550,000 ohms. So what is the AMPS used by R1? I=E/R .... so 215 divided by 550000 equals 0.0003909 Amps. Now we know the AMPS will be the same through R1 and R2 because they are in "series" (on the other side of the bridge rectifier). So Resistance equals Volts divided by amps. R=E/I..... 5volts divided by 0.0003909 equals 127900 ohms or... 12.79 K ohms. We get SLIGHTLY different answers because of the long decimal answers that I shorten a little when entering them into the calculator. ALSO.... my answer will not be totally accurate because of the bridge rectifier in the middle that I did not compensate for. 12.7 K will get you close.

Remember that if you attach any LOAD to the rectifier in PARALLEL with the R2 resistor.... then the voltage will go lower because you are adding resistance (load) in parallel with R2. The LOAD ITSELF (without adding any R2 resistor)... should measure 12.7K for this to have 5 volts (thereabouts) across it.

Can you give me a circuit which gives 5 volts as output with these components actually i need a schematic of that circuit ?

Please!!

Super Good Warning !

There is no galvanic isolation between the 5V DC and main 220V AC! This means, the circuit and any load connected has to be treated as a high voltage device - double isolation, non conductive housing, protection against contact, grounding of any touchable metal parts...

And framistan is right, the resistors have to have the right wattage, but they (and the capacitor and diodes as well) have to be rated for the voltage too! This means, you can't use a SMD resistor or a 1N4148.