# can i convert 230v ac to 12v dc by a resistor & diode ?if can what is the amount of them ?

iceng1 year ago

makes me forget the ultimate solution circuit........................oh oh goonnnnn
GovindG1 year ago
the real quest by Tvibakar is that he dont want use transformer for step down the voltage .. so he will have to use the same method as suggested but can u suggest some other alternative because the power dissipation and losses using the diodes and resistors will be more .
tvibakar1 year ago
Kindly suggest me a circuit which is given 230V AC supply and producing 18-20V DC output without the application of transformer in the input side.
1 year ago
That is a silly question without specifying the current or power :-)
1 year ago
Sorry sir. I failed to specify the current rating as you said. Actually I need a 20V 1 A power supply which is given input 230V AC supply. I need a circuit without the application of transformer to convert 230V AC supply to 20V dc supply. I got some circuits but the current rating is under 50mA. Is it possible to use a bridge rectifier instead of transformer for an current rating 1 A.
1 year ago
No Transformer ( XFMR ) to lower the 300V takes a lot of Resistor Power.

The output will be DANGEROUS enough to Kill you ! ! !

First the peak volts are Line x 1.414 = 325V
Subtract the 20V output gives a rough 300V you must dissipate.
For many reasons we will use two resistors...
R1+R2 = VR / I = 300 / 1 = 300 ohms or 150 + 150 ohms
Now power = V x I = 300 x 1 = 300 Watts or 150 HUGE Watts each
The Zener is 20V x 1 Amp = 20 Watts means a STUD Zener

The rest is clear in the pic.
Hope you realize this is why you don't want to try.

A
iceng3 years ago
Thanks for your kindness. I am / was a true comment answer to this horrididle.
My comments still stand to our silent author about his desired current.
Except to add, the circuit is the equivalent what rickharris suggestion of
acquiring a wall wart...............A
orksecurity3 years ago
As others have said: Not safely, not easily, and even if you had the right resistor, a full-wave rectifier, and capacitors you're going to get a lot of 60Hz noise on the line. Plus, voltage will vary as the amount of current the thing you're powering draws varies. Bad solution all around.

If you need a 12V power supply, use an isolated, regulated 12V power supply circuit.

(Iceng: If you care about such things, you might want to repost your reponse as a top-level answer so it can be marked as Best Answer. Instructables still doesn't permit giving that accolade to a sub-response, only to an entire thread. Or maybe you don't care -- I don't, overmuch, but since I'd sorta like to see my percentage come up one notch I've been keeping it in mind.)
steveastrouk3 years ago
Unless you really, really know what you are doing, I'll say "Never", and in many years of practice, I've also never needed to provide supply to a device with a non-isolated power supply.

Non-isolated supplies are very dangerous.

Avoid.
rickharris3 years ago
iceng3 years ago
NO  you cannot do it without a Capacitor and even then it will be Horrible.

Say you want 0.9 Amp at 12VDC and you have a 400 VDC  50 uF capacitoryou will need a 337 ohm Huge 300 watt resistor.

Use a 230 VAC to 24 VAC transformer first to lower the voltage
then use a DC bridge to rectify the low volt AC to DC add a capacitor
and a 12VDC regulator and a final filter capacitor.

You need to decide how much current EXACTLY  if  you want to use the
single resistor in place of the regulator.