I am working on a transformerless PSU for maiking a 3nos.x3 watt led, each having forward voltage around 3.6v and current around 650-700ma.
I have worked on this kind of circuit:
I guess a 1uf 400vac cap at C1 will offer current around 70-80ma, but here I need a current output at around 8-9 time above this. Means around 600-700ma. I am assuming a Vout at 12v dc (where input is 220vac), where 3 of 3 watt led's are connected in series.
Can anyone explain how can I get such an output from this circuit, means what value of C1 and R1 should be used here. Is there any theoretical formula to calculate the output of such a capacitive circuit, or I should say how do I know what value of C1 can give me an output (Iout) of a specified value. Though I have used This, for calculating the same but I can't derive the relation with the led circuit. Any help is appreciated.
Best Answer
If C1 was directly connected across L and N and takes a current of 80mA when the input voltage is 220V AC, then that is the limit of this circuit. Using a "transformer" is the only way you can increase this current.
By "transformer" I mean a conventional magnetic coupled transformer or a switching regulator that may or may not use a transformer.
If you are intent on pursuing this approach you'd need to have a capacitor value of at least 10uF - at 50Hz it's impedance is 318 ohms and with 220V across it there will be a current of about 0.7A.