230V AC Mains to 5V DC Converter

Thread Starter

vaibh_p

Joined Jan 11, 2020
20
Hello AAC members,

I am designing low cost circuit for controlling AC-powered appliances with a very small micrcontroller.
For that I have designed the power-supply circuit which converts 230V AC to 5V DC.

The circuit works fine in Proteus Simulation.
But when I tried on actual circuit , the output before connecting the 7805-IC is 8.5V DC, however when I connect 7805 to the circuit , the voltage at input of 7805 suddenly drops to 2-3V and thus output at 7805 will be 0.2-0.3V.

So I need help what is the issue that causes voltage drop at input of 7805 when it is connected ?

Also at the output of 7805, I want to drive the small controller , so is there any other possibilities that it will go wrong ?
 

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ronsimpson

Joined Oct 7, 2019
1,753
What could be wrong?
C2; is it a 700 to 1000V part?
7805 is it backwards? Check the pinout.
The 0.47uF cap can only produce 10mA. (math done in my head) What is the load on the output of the 7805? The Quiescent current of the 7805 is 1/2 of that. So you can hardly get any current from the regulator.

What micro are you using? Can it run from a not well regulated supply. Many parts can run from 3 to 5 volts.
----------------
I just built one and the current is very low.
 
Last edited:

ronsimpson

Joined Oct 7, 2019
1,753
I have made many of these. Here is one in SPICE.
1N4001 or 1N914 will work. You do not need a 1000V diode.
By using 4 diodes I get twice the current. 20mA in this case. 50hz.... you will get more current at 60hz.
D2, D3 are 4.7 or 5.1 V Zeners to do the regulation. With a small load the voltage will be the Zeners voltage - 0.7 volts.
1638236105139.png
 

MaxHeadRoom

Joined Jul 18, 2013
24,252
Have you considered galvanic isolation for the 5V?
If not and the circuit is not isolated you will need to consider implementing a earth safety GND for the end devices.
 

ronsimpson

Joined Oct 7, 2019
1,753
All the devices I made like this are in a double layer box. You can not bring out any wires. Even the buttons must have two pieces of plastic to the finger. No vents. ....... That only maters if you will put it on the marked or don't want to kill someone.
[B]vaibh_p[/B], You know this is dangerous! It is sitting on the powerline not ground.
 

panic mode

Joined Oct 10, 2011
1,997
this is meant for low power (low current) applications. so anything that also consumes "significant" current is to be avoided. and your 7805 may be just that. so what is the exact brand/version of your 7805? some have low bias current, some not so. if you are expecting 10-15mA of output current, some 7805 will be a problem, their bias current (quiescent current) may be a major factor. if you need more current, then impedance of the circuit need to be reduced. this means going for larger value of capacitor C2 and lower value of resistor R1 in your circuit. in one posted by Ron, R1 and R2 are opposite from your circuit so if you follow his diagram, C1 would need to be larger and R2 lower. his circuit is clever as it completely removes regulator and it does full wave rectification (more current and less ripple with same size filter capacitor). output voltage is a bit lower than 5V but acceptable for many applications.

so start by stating your requirements (voltage AND current).
you need 5V and 200mA? that is a lot more than values listed are good for.

consider this example:

1638250684878.png
as you can see load resistor gets only 2V or so.
guess what happens if you change capacitor value:
1638250709409.png
 

Thread Starter

vaibh_p

Joined Jan 11, 2020
20
I don't see step down transformer in your circuit.

I think you should read more about what topics given below

  • Step down transformer
  • Rectifier
  • Filter capacitor
  • Voltage Regulator
  • Load
Hello Pushkar1 ,
Actually I want to make very compact and cheap circuit , and then I have found such circuit on web.
My aim is to achieve 5V_DC_100-150mA current from 230V_AC.
 

Thread Starter

vaibh_p

Joined Jan 11, 2020
20
I have made many of these. Here is one in SPICE.
1N4001 or 1N914 will work. You do not need a 1000V diode.
By using 4 diodes I get twice the current. 20mA in this case. 50hz.... you will get more current at 60hz.
D2, D3 are 4.7 or 5.1 V Zeners to do the regulation. With a small load the voltage will be the Zeners voltage - 0.7 volts.
View attachment 253859
Hello ronsimpson,
So is there any component that to be replaced to achieve higher current say around 150mA.

Or if can you suggest any other circuit that outputs 5V_DC_100-150mA Current.
Thank you.
 

Pushkar1

Joined Apr 5, 2021
416
Hello Pushkar1 ,
Actually I want to make very compact and cheap circuit , and then I have found such circuit on web.
My aim is to achieve 5V_DC_100-150mA current from 230V_AC.
Can you explain what is your main objective?

Do you want to learn how to design a power supply circuit that converts 230V AC to 5V DC ?

If you need a power supply of this specification for the project you can use a USB charger adapter. As already suggested by @MrChips
 

Thread Starter

vaibh_p

Joined Jan 11, 2020
20
Can you explain what is your main objective?

Do you want to learn how to design a power supply circuit that converts 230V AC to 5V DC ?

If you need a power supply of this specification for the project you can use a USB charger adapter. As already suggested by @MrChips
Yes USB charger circuit will serve the purpose , but I need Small-Cheap circuit for my project and there I found the circuit with just combination of capacitors, resistor and Diodes. I guess the output current is the main concern know , so any suggestions to increase the output current ?
 

Pushkar1

Joined Apr 5, 2021
416
Yes USB charger circuit will serve the purpose , but I need Small-Cheap circuit for my project and there I found the circuit with just combination of capacitors, resistor and Diodes. I guess the output current is the main concern know , so any suggestions to increase the output current ?
you have not answered my question. Still you haven't clarified what you will do with this power supply.

What equipment do you want to power with this power supply?

Do you want to develop it for commercial purpose?
 

Thread Starter

vaibh_p

Joined Jan 11, 2020
20
you have not answered my question. Still you haven't clarified what you will do with this power supply.

What equipment do you want to power with this power supply?

Do you want to develop it for commercial purpose?
I want to drive small microcontroller based circuits for dedicated operations.
No , I am not going commercial , I just want it to control several appliances of my room , that's why looking around the web for any similar circuit.
 

MaxHeadRoom

Joined Jul 18, 2013
24,252
Surely you have access to a small power supply from most portable devices you may already have where you can make safe a isolated version?
The common 'Wall-Warts' are also very cheap.
 

AnalogKid

Joined Aug 1, 2013
9,639
I need help what is the issue that causes voltage drop at input of 7805 when it is connected ?
The impedance of C2 at 50 Hz is 6.77 K ohms. The static current of a 7805 is 5 mA. In your simulation, replace C2 with a 6.8 K resistor, add a 10 mA load on the 7805 output, and recalculate.

ak
 

DickCappels

Joined Aug 21, 2008
8,169
These power supplies that use voltage dropping capacitors are, in my experience, used for inexpensive products that are isolated from the user. The first one I saw was in a rechargeable flashlight. That's a good application for it.

I have made a few of these, but like ronsimpson, they have all be enclosed in sealed plastic boxes that are completely isolated from people's fingers. I've used them to drive fans, light bulbs, and soldering irons. That's about it.

Recently I picked up a bunch of those little USB cubes -some have substantial output capabilities and I plan to use those expensively in future projects. They are cheap and once they pass a ground leakage test, I consider them safe. Buying and protecting a simple voltage dropping circuit and regulator would probably cost quite a bit more. At least the USB chargers are (supposed to be) isolated from their outputs, and that's easy to test. Other than the little isolated devices, I have not built an AC power power supply for more than 10 years, its just not worth having to worry about personal safety and fires...and waht about qualified components?
 

Thread Starter

vaibh_p

Joined Jan 11, 2020
20
These power supplies that use voltage dropping capacitors are, in my experience, used for inexpensive products that are isolated from the user. The first one I saw was in a rechargeable flashlight. That's a good application for it.

I have made a few of these, but like ronsimpson, they have all be enclosed in sealed plastic boxes that are completely isolated from people's fingers. I've used them to drive fans, light bulbs, and soldering irons. That's about it.

Recently I picked up a bunch of those little USB cubes -some have substantial output capabilities and I plan to use those expensively in future projects. They are cheap and once they pass a ground leakage test, I consider them safe. Buying and protecting a simple voltage dropping circuit and regulator would probably cost quite a bit more. At least the USB chargers are (supposed to be) isolated from their outputs, and that's easy to test. Other than the little isolated devices, I have not built an AC power power supply for more than 10 years, its just not worth having to worry about personal safety and fires...and waht about qualified components?
Thaknk you DickCappels,

so could you suggest any point what's gone wrong ? or any circuit for required output of 5V/100mA.
 
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