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

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the answer is yes. but more probably it may not be that useful for high rated loads it cannot drive high power loads.The circuit is as simple as converting 12-0-12v of transformer to 12v by means of bridge rectifier here also you can use high power diodes to convert.later on you may get a voltage of around 230v pulsating dc which can be converted to 12 v by potential divider method.connect R1 an R2 in series and output across R2 and its voltage id R2/(R1+R2).

iceng3 years ago
ameerali does not know about best answer by now,

makes me forget the ultimate solution circuit........................oh oh goonnnnn
GovindG3 years 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 .
tvibakar3 years 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.
iceng tvibakar3 years ago
That is a silly question without specifying the current or power :-)
tvibakar iceng3 years 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.
iceng tvibakar3 years 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.

iceng4 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
orksecurity4 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.)
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.

rickharris4 years ago
Not successfully, best answer - buy a wall wart converter.
iceng4 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.

adam 1014 years ago

If you do that you will get very inconsistent power. Instead use a transformer and rectifier. A ratio of about 20 turns to 1 would work for a transformer. Then use a 4 diode rectifier  like this:


If consistent Voltage is important then add a Voltage Regulator


You can go down to Wal-Mart Radio Shack (that's not just a US thing right?) Or Whatever and pick up a 12 volt wall wart if you can't do the above.