12V 2A power supply with 1M ohm resistor, 1uF 250V capacitor and 1N5408 diode

Thread Starter

taharat

Joined Mar 31, 2021
2
Hello everyone.

I have seen many videos on YouTube where they built a capacitor based 220V AC to 12V DC power supply. But those were not sufficient for my project. I am eager to build a 12V 2A power supply where the input will be 220V 50 Hz using the following components:

105K 250V ceramic capacitor
1M ohm resistor
1N5408 diode
12V zener diode
1000uF 25V electrolytic capacitor

You can add additional components to the circuit but the above mentioned ones must stay.

Thanks in advance!
 

AlbertHall

Joined Jun 4, 2014
11,095
You cannot make a capacitor input supply for 2A output.

A 220V to 9V transformer (for an unregulated supply) or a 220V to 12V transformer for a regulated supply), both rated for at least 3A.
For the regulated version you will also need a regulator, for instance an L78S12CV, and a decent heatsink for the regulator.
It would be better if you had 4 of the 1N5408 to make a bridge rectifier.
 

Tonyr1084

Joined Sep 24, 2015
5,802
If you need a 12 volt 2 amp supply you can generally get them for free at any Xfinity store or Satellite store. When people return their old units with power supplies they don't reuse the supplies. I get them often for free from Xfinity. I'm confident DirecTV will likely also give them away. Their other option with returned supplies is to recycle them (toss them in the trash).

Depending on where you are, this IS a World Wide Web forum. Outside the United States - I don't know if you can get such items for free. Certainly, if I worked at one of those stores I'd be bringing those supplies home and selling them cheap on eBay as "USED" power supplies.

Your profile doesn't tell us where you're from, so I can only guess.

Finally, welcome to AAC.
 

schmitt trigger

Joined Jul 12, 2010
412
You can simply throw random components and expect a particular circuit outcome.

Design works the other way around:
one decides upon a particular circuit configuration; afterwards you calculate, simulate and then and only then, select the required components to perform the task.
 

DickCappels

Joined Aug 21, 2008
7,147
25 watts out of a capacitive voltage dropping power supply? Why is it that you would go with a capacitive voltage dropping supply when there are other more reliable, safer approaches?
 

dendad

Joined Feb 20, 2016
3,781
I would always recommend an isolated power supply, and the capacitive one is not so it is potentially VERY dangerous.
Those Youtube videos are bordering on criminal in my opinion. Although this sort of power supply is used in special cased, and in well insulated cases too, they are not suitable for general use.
Folks with little electrical knowledge build them and then get killed, or worse yet, damage someone else. Please stay away from them, and follow the advice given above.
Go with a transformer or an old power supply.
A very good source of power supplies is laptop 19V power supplies. Then add a buck regulator to give you the required voltage.
 

DickCappels

Joined Aug 21, 2008
7,147
Interesting to think about this, but a 24 watt power supply using a transformer is likely to weigh much less than one using a voltage dropping capacitor, and it would not only be safer but last a lot longer.

(If you have not noticed, the idea of a 24 watt power supply based on a capacitive voltage dropper is getting a lot of support.)
 

Yaakov

Joined Jan 27, 2019
2,341
Interesting to think about this, but a 24 watt power supply using a transformer is likely to weigh much less than one using a voltage dropping capacitor, and it would not only be safer but last a lot longer.

(If you have not noticed, the idea of a 24 watt power supply based on a capacitive voltage dropper is getting a lot of support.)
Yes! This document (https://ww1.microchip.com/downloads/en/appnotes/00954a.pdf) thoroughly covers calculating component values and ratings for capacitive and resistive supplies and 2A is a rather big ask for this circuit.
 

Ian0

Joined Aug 7, 2020
1,540
Don't forget that a capacitive dropper circuit draws the same current from the mains as its output current. So for 12V 2A output, you will need 2A of mains input (whether your mains is 230V or 110V)

If I were to add anything to your list of components to make a 2A 12V power supply, the component I would add is a transformer.
 

Thread Starter

taharat

Joined Mar 31, 2021
2
Thank you everyone for your valuable opinion. Actually I saw those and became interested but because of lack of experience I thought of taking expert opinion before approaching. Thank you again for your time.
 

dendad

Joined Feb 20, 2016
3,781
I'm pleased you will take notice of the advice.
Some new posters get upset when told what they want to do is unwise or unsafe.
We want folk to keep safe and enjoy the electronics hobby.
 

crutschow

Joined Mar 14, 2008
26,721
Don't forget that a capacitive dropper circuit draws the same current from the mains as its output current. So for 12V 2A output, you will need 2A of mains input (whether your mains is 230V or 110V)
True.
But much of that is reactive current, so does not draw that much real power from the mains.
 

Ian0

Joined Aug 7, 2020
1,540
True.
But much of that is reactive current, so does not draw that much real power from the mains.
Quite a few people have been caught out by that as a lot of cheap LED lamps are capacitive-dropper, and when there are a dozen on a circuit, the current soon adds up!
Obviously the same applies to inductive-ballast fluorescent and other discharge lamps, be we generally correct that with a power-factor correction capacitor.
 
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