The relationship between capacitive reactance (X), capacitance (C) and output current (I) is expressed as:
As a safety measure, R2 (470-kilo-ohm) is placed in parallel to C1 as a bleeder resistor. It removes the stored current from C1 when the power supply is disconnected from the mains. This prevents shock hazards, since the capacitor stores more than 400 volts when fully charged. This current may be present in the capacitor for many days even after the circuit is switched off.
Power considerations
Since the circuit is directly connected to high-voltage AC, power rating of the components is important. Capacitor C1 must be X-rated type with a voltage rating of 400 volts or more. The power rating of resistors R1 and R2 must be high enough to handle AC.
Current through R1 is full-wave current, so it is equivalent to the line voltage divided by the impedance of C1. Therefore R1 and R2 must be rated at 1 watt.
Diodes D1 and D2 are rectifiers. Maximum RMS current passes through D1 and D2. So the peak inverse voltage of the diodes must be sufficient to handle this high current. Diode 1N4007 is a good choice as it can handle 1000 volts and 1A current.
Capacitor C2 smooths rectified DC and acts as a buffer to release current to the load. The value of C2 should be double the voltage rating of the zener diode. A 25V electrolytic capacitor will work smoothly.
Zener diode ZD is used to regulate the output to 9.1 volts. It is subjected to most of the current in no-load condition and will get most of the full-wave current once C2 is charged. So the power rating of ZD must be sufficient to handle this high current. Maximum power dissipation that can be allowed in the zener is the zener voltage multiplied by the current flowing through it. If the 9.1V zener passes 35mA current, its power dissipation will be around 318 mV. So a zener rated at 400 milliwatts or more can be safely used.
Resistive power supply
In contrast to the capacitive type, a resistive power supply uses the property of resistance to limit the current. As with the capacitive type, the output voltage will remain stable as long as the output current is less or equal to the input current. Resistive power supply is cost-effective and requires less space for its accommodation. But severe power loss through heat is an important drawback. Like capacitive type, it also has no isolation from mains. The output supply is less energy-efficient compared to a capacitive power supply.
Fig. 3 shows the design of a simple resistive power supply. Before making a resistive power supply, power rating of the components needs critical consideration. All the components should have sufficient current capabilities. Since the resistor is used to drop voltage and current from the mains, power rating of the resistor is important to avoid burnout. Table II shows the current-handling capacity of various types of resistors.
This article is an example of what we get when a professor of zoology tries to write articles on Electronics!
Lot of nonsense has been written in this article to confuse hobbyists and students.
For example, 230V/14.4 = 15.9 mA? It is simple Ohms Law, and the answer is not mA but AMPERES, yes, the answer should be 15.9 AMPERES! Mr Mohan Kumar, just try to connect a 14.4 ohm resistor across the 230V mains and you shall get your answer….It seems that the author has never actually done any practical projects in electricity or electronics himself.
You are right. Teoretical is one thing and practical work is the other. The difference between these two is big.
And mentioning theoretical work earlier, in this article the author doesn’t seem to work a lot on theoretical knowledge either 😀
Chinmoy Mitra what you have told is wrong. Mohan kumar is right since the reactance of capacitor for 0.22uF capacitor is 14.4 K ohm and thus the 230/14.4*10000=15.9mA.
It’s because the capacitor’s value is incorrect. It is supposed to be 225K value (22uF), which will then give you the rest of these values. 0.22uF or 220nF will give you 14.4K Ohm.
Hi 225K is 2.2uf not 22uf…
YES SIR,
2.2uf
you are correct.
He may have missed to write 14.4KOhm, just a typing error. But don’t say this way. He has described very well.
Hello sir, I need help about smps circuit it is ac 175 to 230v input and output 24v 2.5amp. Dc so pls give m circuit design. In my mail id. Thank u.
DON’T EVER TRY OUT ANY CIRCUIT by the so called Dr.Mohan Kumar!
Ref: http://www.talkingelectronics.com/projects/SpotMistakes/SpotMistakesP14.html
QUOTE “Professor D.Mohankumar must be the WORST electronics engineer I have ever come across. Here is another of his untested circuits:” Unquote.
Dr.Kumar, plse stop…. U are a source of EMBARRASSMENT to YOUR COUNTRY.
WHAT IS THE PURPOSE OF 9V DC BATTERY in FIG 3?
It ia not thw battery it is the 9V output in the DC form
I like your resanble theroy or cktdiagrm
Hello sir,
I had tried this circuit. I had got perfect output from this circuit. But I had found some problems in this circuit. When the 230v ac is connected to this circuit both the zener diodes got heated in this case. I need solution for this issue. Plz tell me sir..
Mobile charger with all protection like over voltage/under voltage protection over charge cut with indicator with 2AMP cap.5v
Non isolated power supply has risk always follow Isolated .
Can I touch this DC voltage.
You will never know whether neutral or connection is proper or not is the are interchange and you touch the ground of the circuit and same time touching the earth.. It will definitely give you a 240 rms shock.
The author of this article has clearly mentioned that It is dangerous to touch this power supply in page number 5 safety Overall this is a Non isolated power and harm you any time. please refer completely. If it is mandatory to touch better take a insurance and move. (Kidding )
Does this work or not?
If it does work what is the ampage ?
i made this circuit (Fig.9) and used to operate Arduino mini it’s work properly, but R1 resistor is heated too much even I used 3W rather then 1w. please tell me, sir, what is the problem or how can I sort out it?
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Hi dear Schrödinger
Thank you so much for your very useful and informative essay regarding transformerless Power supplies.
would you please answer my questions 😕
1. Is it possible to increase the power of Zener Diods by simply paralleling them? for instance to get one watt by paralleling two 0.5 watt of them?
2. what about increasing Zener Diods’ voltage? for example: to join two pcs. 9.1 and 3.1 volts in series to get a 12 volts Zener diod?
Thank you again
Bye
Hello sir, I need help about smps circuit it is ac 175 to 230v input and output 12v 3.5amp. Dc so pls give m circuit design. In my mail id
the transformer less power supply is dangerous as precautions given ,why then many circuits with ics today uses this type of power supply ?
Dear Sir,
Thank you so much for your very useful and informative essay regarding transformerless Power supplies espesially design considerations.
would you please advice why series resistors and two zener diodes get heated so much and if it is safe to operate the device with such conditions?