Simple Transformerless Power Supply

A very compact simple transformerless power supply circuit is explained here using the concept of capacitive reactance for stepping down the input AC mains voltage.

The Transformerless Power Supply Concept


A transformerless power supply works by using a high voltage capacitor to drop the mains AC current to the required lower level which may be suitable for the connected electronic circuit or load.

The voltage specification of this capacitor is selected such that it's RMS peak voltage rating is much higher than the peak of the AC mains voltage in order to ensure safe functioning of the capacitor. An example capacitor which is normally used transformerless power supply circuits is shown below:

PPC capacitor image for transformeless operation


This capacitor is applied in series with one of the mains inputs, preferably the phase line of the AC.

When the mains AC enters this capacitor, depending on the value of the capacitor, the reactance of the capacitor comes into action and restricts the mains AC current from exceeding the given level, as specified by the value of the capacitor.

However, although the current is restricted the voltage isn't, therefore if you measure the rectified output of a transformerless power supply you will find the voltage to be equal to the peak value of the mains AC, that's around 310V, and this could be alarming for any new hobbyist.

But since the current may be sufficiently dropped level by the capacitor, this high peak voltage could be easily tackled and stabilized by using a zener diode at the output of the bridge rectifier.

The zener diode wattage must be appropriately selected according to the permissible current level from the capacitor.

CAUTION:Please read the caution warning message at the end of the post

Advantages of using a Transformerless Power Supply Circuit


The idea is cheap yet very effective for applications that require low power for their operations.

Using a transformer in DC power supplies is probably quite common and we have heard a lot regarding it.

However one downside of using a transformer is that you cannot make the unit compact.

Even if the current requirement for your circuit application is low, you have to include a heavy and bulky transformer making things really cumbersome and messy.

The transformerless power supply circuit described here, very efficiently replaces a usual transformer for applications which require current below 100 mA.

Here a high voltage metalized capacitor is used at the input for the required stepping down of the mains power and the preceding circuit is nothing but just simple bridge configurations for converting the stepped down AC voltage to DC.

The circuit of a cheap transformerless power supply shown in the diagram above is a classic design of a transformer less power supply circuit and may be used as a 12 volts DC power supply source for most electronic circuits.

However having discussed the advantages of the above design, it will be worth focusing on a few serious drawback this concept may include.

Disadvantages of a Transformerless Power Supply Circuit


First, the circuit is unable to produce high current outputs, but that won’t make an issue for most of the applications.

Another drawback that certainly needs some consideration is that the concept does not isolate the circuit from dangerous AC mains potentials.

This drawback can have serious impacts for designs which have terminated outputs or metal cabinets, but won’t matter for units which have everything covered up in a non-conducting housing.

Therefore, new hobbyists must work with this circuit very carefully to avoid any electrical casualty. The last but not the least, the above circuit allows voltage surges to enter through it, which may cause serious damage to the powered circuit and to the supply circuitry itself.

However in the proposed simple transformerless power supply circuit design this drawback has been reasonably tackled by introducing a high voltage capacitor after the bridge.

This capacitor grounds instantaneous high voltage surges, thus efficiently safeguarding the associated electronics with it.

How the Transformerless Power Supply Circuit Works


The working of this transformless power supply can be understood with the following points:

  1. When mains AC mains input is switched ON, capacitor C1 blocks the entry of the mains current and restricts it to a lower level as determined by the reactance value of C1. Here it may be roughly assumed to be around 50mA.

  2. However, the voltage is not restricted, and therefore the full 220V or whatever may be at the input is allowed to reach the subsequent bridge rectifier stage.

  3. The bridge rectifier rectifies this 220V C to a higher 310V DC, due to the RMS to peak conversion of the AC waveform.

  4. This 310V DC is instantly reduced to a low level DC by the next zener diode stage, which shunts it to the zener value. If a 12V zener is used, this will become 12V and so on.

  5. C2 finally filters the 12V DC with ripples, into a relatively clean 12V DC.





PCB Layout for the above explained simple transformerless power supply is shown in the following image. Please note that I have included a space for an MOV also in the PCB, at the mains input side.


PCB track layout design for transformerless power supply

Example Circuit for LED Driver Application


The following transformerless or capacitive power supply circuit could be used as an LED driver circuit for illuminating minor LED circuits safely, such as small LED bulbs or LED string lights.

The idea was requested by Mr. Jayesh:

Requirement Specifications

The string is made up of about 65 to 68  LED of 3 Volt  in series approximately at a distance of let us say 2 feet ,,, such 6 strings are roped together to make one string so the bulb placement comes out to be at  4 inches in final rope . so over all  390 - 408    LED bulbs in final rope.
So please suggest  me best possible driver circuit to operate
1) one string of 65-68 string.
or
2) complete rope of 6 strings together.
we have another rope of  3 strings.The string is made up of about 65 to 68  LED of 3 Volt  in series approximately at a distance of let us say 2 feet , such 3 strings are roped together to make one string so the bulb placement comes out to be at  4 inches in final rope . so over all  195 - 204    LED bulbs in final rope.
So please suggest  me best possible driver circuit to operate
1) one string of 65-68 string.
or
2) complete rope of 3 strings together.
Please suggest the best robust circuit with surge protector and advice any additional things to be connected to protect the circuits.
and please see that circuit diagrams are with values required for the same as we are not at all technical person in this field.

Circuit Design

The driver circuit shown below is suitable for driving any LED string having less than 100 LEDs (for 220V input), each LED rated at 20mA, 3.3V 5mm LEDs:



suitable for driving any LED string having less than 100 LEDs


Here the input capacitor 0.33uF/400V decides the amount of current supplied to the LED string. In this example it will be around 17mA which is just about right for the selected LED string.

If a single driver is used for more number of similar 60/70 LED strings in parallel, then simply the mentioned capacitor value could be proportionately increased for maintaining optimal illumination on the LEDs.

Therefore for 2 strings in parallel, the required value would be 0.68uF/400V, for 3 strings you could replace it with a 1uF/400V. Similarly for 4 strings this would need to be upgraded to 1.33uF/400V, and so on.

Important: Although I have not shown a limiting resistor in the design, it would be a good idea to include a 33 Ohm 2 watt resistor in series with each LED string for added safety. This could be inserted anywhere in series with the individual strings.

WARNING: ALL THE CIRCUITS MENTIONED IN THIS ARTICLE ARE NOT ISOLATED FROM MAINS AC, THEREFORE ALL THE SECTIONS IN THE CIRCUIT ARE EXTREMELY DANGEROUS TO TOUCH WHEN CONNECTED TO MAINS AC........

Need Help? Please send your queries through Comments for quick replies! And please Bookmark my site :)




Comments

Swagatam said…
you can use a 5.1V zener in place of the shown zener, 0.22uF will not work because it won't be able to support the relay.
Abu-Hafss said…
Hi Swagatam

Is it possible to have current in between 100mA and 200mA?
Swagatam said…
Hi Abu-Hafss,

It is possible, provided the load voltage is rated at the input mains level, otherwise most of the current would drop producing no significant enhancement in current.
Justin Adie said…
Hello

is input polarity important in this design? e.g. in many european countries there is no wiring standard to dictate which wire/pole is the phase and which is the neutral. and even if there were, the plugs can just be reversed.

and if input polarity is not important could you give a brief explanation why?

many thanks
Justin Adie
Swagatam said…
For mains AC inputs the polarity is never critical because of its alernating nature which oscillates from positive to negative at the specified frequency, in your area and India it's 50Hz (50 cycles per second), therefore the polarity is undefined and becomes immaterial.
Justin Adie said…
so it doesn't matter that the filtering circuit is on the neutral (tied to ground) rather than the phase?

is that true even for electrical systems that do not tie neutral to ground?

and does that also mean that it makes sense to put fuses at both terminals of this kind of AC circuit?
Swagatam said…
It doesn't matter to the circuit operation, but certainly matters to living beings in terms of getting or avoiding a lethal shock.

Therefore when it comes to adding a fuse, it must be always added to the phase line, never to the neutral.

Justin Adie said…
and therein lies the problem! In my country (France) there is _no_ way to determine visually which line is the phase and which the neutral. the plugs and sockets are not physically polarised.

so what is the recommendation? to fuse both lines?

Swagatam said…
You can simply identify them by using a line tester device, the touching the tester to the relevant lines will provide an illuminated neon indication for the phase line and no illumination for the neutral.
Justin Adie said…
yes. however that is not practical when the power supply and device are in their container and freely movable by the consumer from socket to socket.

it is not, of course, reasonable to require a user to have a phase tester and insert it into a socket to test (and in fact for security reasons it is not quite that simple either).

i guess by not answering the question about fusing you are indicating either that it is not safe to use this circuit when there is no visual way to determine phase or you do not have an opinion on whether it is good practice (and effective) to fuse both poles.

as always, thanks for your time.
josef said…
Hii...

what will be the voltage across the output terminals for this circuit, given that the Zener diode is not used for regulation?

Also, does the AC capacitor(PPC) act as the series reactance as opposed to the Series resistance(Rs) in a standard Zener Voltage regulator circuit?
Swagatam said…
The voltage will be always equal to the input mains peak, for 220V AC it would be 330V DC.

In presence of load, whether a zener or any other load, the reactance behaves like a resistance and restricts current as per the load.
Shriram S said…
Sir i want to replace a 12-0-12 transformer in one of my projects with this transformerless power supply you have mentioned here. I want your help in implementing it, would you please guide me on how to do it, whether i can use the same circuit mentioned above or any changes are required.
Thanks in advance
Swagatam said…
Hi Shriram, what is the current requirement of your circuit? If it's above 100mA then capacitive power supplies as described above should not be used
How much AMPERE is this 12V transformerless,?
Do you have a 12V 1A transformerless? Or 2A
Swagatam said…
presently i don't have it.
Fazal Ellahi said…
hi dear SWAGATAM
if i need only 5v from this circuit then can i use 5v zener diode in it
help me to produce 5v
Swagatam said…
Hi Fazal, yes you can use a 5V zener to get a 5V output from this circuit.
jason bobis said…
Hello Swagatam Majumdar.. How can I make the output of this power supply be 12V 1A?
Swagatam said…
hello Jason, getting current above 100mA is not recommended for capacitive power supplies...because it could dangerous for the connected load under those specs.
Jagdeep Singh said…
Sir
I made this circuit but sum time after r2 is burn
Help me
Swagatam said…
Jagdish, use 474/400V in place of 105/400V
Pete Skinner said…
have two TM-619-2 timers that work on 220v.Would like to run a 120v. Uses transformerless cap power supply. Components are .33uf cap with 1M ohm resister in parallel as well as 180 ohm resistors in series on both sides of 220v input. Bridge rectifier follows. Can you help?
Swagatam said…
you can use the same circuit with 120V also, the output result from transformerless supply would be the same as for 220V.
Pete Skinner said…
They also have model TM-619-1(120vac) and TM-6331(120/220vac). When I plug in the 619-2(220vac) to 120vac the timer portion will work but the power supply is suppose to convert to 24vdc to run a relay which it is not doing. I have 2 brand new and neither will switch relay running at 120vac.
Swagatam said…
you ca try increasing the value of the 0.33uF cap by putting another 0.33uF parallel to it or by replacing it with a 0.68uF/250V cap.
Pete Skinner said…
I did try a .47uf with no luck but will try with a .68.uf. Thx for quick response! Great name by the way Swag.
Swagatam said…
sure Pete! thanks, my pleasure:)
Fazal Ellahi said…
oh thanks a lot dear
ravindra metri said…
Above circuit can i use in your Li-ion Emergency Light Circuit with Over charge and Low Battery Cut off Features circut. Instead off cellphone charger circuit
Swagatam said…
No, it won't charge Li-ion batt
ravindra metri said…
Sir. Plz give ac oprated mobile battery li - ion batt circuit
BlogSerba said…
Have u made it?
my friend said we can't put resistor facing 220 volt AC
Swagatam said…
a resistor can be inserted anywhere in a circuit for suppressing surge, the position is never critical.
Deepam Paul said…
Hello Sir;
I want to try this circuit for Making LED series for Diwali. I try to test this circuit using Circuit design PCB software but in this software there is no 250v electrolytic capacitor so i use 200v electrolytic capacitor so it give me a voltage of approximately 13V but i am satisfy with output current . My Doubt is if i use 250v electrolytic capacitor then it will give the 12v output voltage or less than 12 . And how much watt is R1.
Please tell me some PCB design software which use AC power supply component and can run stimulation test.
Swagatam said…
Hello Deepam,

200V capacitor will also do, this voltage is not relevant to the the output voltage of the circuit, the zener diode is responsible for it.

Don't use simulators, they are very unreliable and mostly give misleading results.
Swagatam said…
R1 will be always 1/4 watt
Raja Banerjee said…
Surprisingly in cheap led bulbs available in the market, they use 474K /250V main cap and no filter cap.and they are doing good... Now how these bulbs servibe in the 240 V mains?? thanks
Swagatam said…
Yes it's possible, I'll try to address it soon in my blog

Abu-Hafss said…
Hi Swagtam

Can this supply be used to power up the following project:

https://homemade-circuits.com/2014/06/energy-saver-solder-iron-station-circuit.html

I am bit concerned about the voltage surges.
Swagatam said…
Hi Abu-Hafss,
although I too don't recommend capacitive power supplies for operating sophisticated electronic circuits, the above circuit could become relatively safer if C1 is reduced to 0.47uF/400V....the zener diode is crucial here and should not be removed from the circuit.
there isn`t 50 ohm/1w resisiton to find then what can i use to that?
Swagatam said…
the value is not critical, you can try other values such 33, 47 68, ohm etc.
Nirvikal Lal said…
I want to convert 230 or 220 vac to 5 or 6v dc without transformer so pls help me it's urgent i need for a project
Swagatam said…
you can try the circuit discussed in the above article....use a 5V zener at Z1, and 0.33uF/400V for C1
Ritwik Ghosh said…
can you please explain the function of R1 and C1 ?
i mean why they are in parallel ?
Swagatam said…
R1 makes sure that C1 gets discharged immediately while someone unplugs the unit from the mains socket, thus cancelling any chance of an electric shock to the user from C1 discharge
basit momin said…
For wat purpose the circuit can be used for..........
Swagatam said…
for powering any DC circuit below 50ma
can i use regulator ics instead of zenar dode?
what is the dc output after the rectifier, without using the zenar ( capacitor is not removed)
Swagatam said…
yes regulator ICs can be used, without a zener it would be restricted to the capacitor's breakdown voltage rating.....but that would create a lot of stress of the capacitor
Saqib Mehmood said…
Plz just tell me how capacitor contribute in step down ac voltages and what value of capacitor we will choose for 220-6v and how???plzzzz
Swagatam said…
capacitor steps down the current not the voltage...voltage is controlled by the zener diode
pakol27 said…
Can I use this circuit to power 12v computer Fan?
Swagatam said…
yes, but at a slower speed...
pakol27 said…
What should i do to maximize the speed of the fan?
Swagatam said…
add anther capacitor parallel with C1
pakol27 said…
Thank you Swagatam.. Can you give the modified circuit? Just to make sure that I make this right.
Swagatam said…
My pleasure pakol, make C1 = 2uF/400V that's all, and preferably use a 12V 2 watt zener.
khant hnin said…
Please help me.Can I use 2uF/400V for C1?
1uF/400V is not available near my area.
Swagatam said…
2uF will cause more surge current to flow into the circuit....you may use it, but make sure to employ two zener diodes in parallel each rated at 1 watt
Arun Das said…
sir can u help me to convert 230v ac to 110v ac ...step down circuit
Swagatam said…
Arun, you'll need an auto-transformer for that

you can wind 300 turns of magnet wire (25SWG) over an iron laminated core (transformer E core) and connect the ends to the 220V, the 110V may be collected from anywhere at the middle of the winding
binu said…
Sir good work. But what is the use of r2 50ohm 1w resistor. Can I use 100ohm resistor instead of this. Plz replay me.
Swagatam said…
Binu, it's for limiting current, you can use lower values than 50 ohms, higher values can cause increased heat for the resistor and lower current outputs
Unknown said…
hello sir
i am tring to make supply from 220v ac to 72 v dc with 2ampere
could u please help me in it
Swagatam said…
sorry I do not have this circuit at the moment...
Abu-Hafss said…
Hi

You can try to find a center-tapped transformer having 220V input and output 36-0-36V rated 2A or 3A. Leave the center-tap and use the remaining two terminals of the transformer with suitable diodes (bridge rectifier) and 1000ยต (or more)/100V capacitor to get 72VDC.
MALAY WANE said…
Hello sir,
I had made this circuit and trying to get output
But whenever i connect zener diode as shown,i gain the output of 1.5v while removing the zener i get 28v so can u plzz tell me where i am getting wrong?
How could i get 12v 1a finally..?
Swagatam said…
Hello Malay, It could be due to a faulty zener diode or may be you are connecting it with a wrong polarity...try replacing it with a new one.

12a/1A from this power supply could be impractical and not recommended.
MALAY WANE said…
Sir i replaced 3 diodes but the problem remains same...every time the diode blows off.
Can i attach any resistor or capacitor in series to diode,and hece collect 12v power.?
Swagatam said…
the zener should be rated at 1 watt...connect a 1N4007 also in parallel to the zener to reduce the stress on the zener...the 1N4007 anode should be connected to the positive line
MALAY WANE said…
I tried this too but it still not working sir.
I am not getting the output.
Instead of zener,can i use any other component?
Swagatam said…
It means your capacitor is faulty...you can try 7812 IC
Harvest Palm said…
Sir, I have made egg incubator timer that you have written on another article, and I want to ask that, can I use this transformerless to be power supply the egg incubator timer circuit that use two 4060 ics?
Swagatam said…
Harvest, no it's not recommended and might not work....use a 12V ad to dc SMPS adapter or a transformer power supply
M- Furqan said…
please sir tell me , i want 220v ac to 60v dc transformerless circuit without transistor
Swagatam said…
you can use the above shown circuit and replace the zener with a 60V zener
Vicky Gowtham said…
hai friend...how can i do my project of mobile charge sharging transfromerless+
Swagatam said…
Hi Vicky, have you previously built an SMPS circuit? if yes then you can try the following design for your requirement:

https://homemade-circuits.com/2014/02/220v-smps-cell-phone-charger-circuit.html
Tiago NET said…
i need a transformerless in this conditions: 6V at 120VAC and 12V at 220VAC! have you circuit for this ?
Tiago NET said…
R2 is NTC for inrush current or power resistor?
Swagatam said…
just change the zener value accordingly in the above shown design...that's all is neeeded
Swagatam said…
R2 is an ordinary resistor but you can definitely replace it with a suitable NTC
beni said…
Thank you Swagatam.
i can not speak english fluently.
i need a transformerless in this conditions:12V,180mA
i use C1 = 2uF/400V , Z1=12V 5 watt zener
output voltage =12.3v
but,while the no-load power, Warm up zener diode.(why the zener diode Heated ! ?)
and too: make two zener diodes in parallel each rated at 1 watt. but zener diode Heated !!!why ?
plz help.thanks.
Swagatam said…
beni, a 5 watt zener is not supposed to get warm, but if it is then you can try adding a 1N4007 diode parallel with the zener in the same polarity, and check the difference.
beni said…
thanks,
i adding a 1N4007 diode parallel with the zener, i use 12V 1 watt zener ,then i use 12V 5 watt zener
the power is OK.OK.
But while the no-load power(If any consumer is not connected to the circuit) Warm up zener diode.
Swagatam said…
you can keep the circuit switched OFF when there's no load connected because anyway without a load it may not be a good idea to keep the circuit switched oN
Arun Kumar said…
I want 12v/300ma transformer less power supply circuit diagram please send link sir
Swagatam said…
https://homemade-circuits.com/2014/02/simple-1-watt-to-12-watt-smps-led.html
kamlesh_sexy said…
Hi friend,
I see that in the above pic, you used 12v zener, so the output of this circuit is 12v.
I did not get 12v 1w zener so I made little changes,
Here is my alteration:
I removed zener and placed with 7812 and replaced c2 with 10uf 16v..
this is correct????
Swagatam said…
Hi friend, yes that will do, but if due to surge current 7812 blows-of then it will be a bigger lose than a 12V zener....put an NTC at the input to solve this issue
can i change the polarity of input(Line and N)?
Sonal Kumari said…
Sir can I use this circuit to power your egg incubator thermostat circuit.
Swagatam said…
no you can't, either an SMPS adapter or a transformer based power supply can be used and is recommended.
Sonal Kumari said…
Sir ,thanks for your previous reply. Can you please recommend me any of your circuits without transformer suit able for the incubator circuit.
Swagatam said…
Sonal, Would you be able to build an SMPS circuit? I don't think so.

So it's better to buy a ready made 12V 1 amp SMPS adapter and use it for the purpose
Waqasafridi said…
Sir I want to make an rechargeable 12v emergency light with battery level indicator without transformer plz help me
Swagatam said…
waqas, similar circuits are already present in this website please search it through the given search boxes...
Davis Kakumba said…
hi swagatam , i made the circuit and its working i used it to power my 12vdc 3w led bulb, now how can i modify it to be used on 240V AC instead of 220v AC
Swagatam said…
Hi Davis, you can use the same circuit for 220V as well as 240V.

3 watt LED will not work with this circuit.
SUDIP BEPARY said…
i have a query about out put from this circuit that if there is variation on input voltage like 220 volt to 180 volt or below, will this circuit change the out put voltage ?
Swagatam said…
NO, unless and until the input AC drops below the zener voltage value
Norman Kelley said…
Hi, Swagatam,
In the above simple transformerless power supply, the circuit shows a reduced DC voltage after the zener diode and a ground connection. What provides the ground. It is not connected to the neutral, so what do I ground the connection to? I'm using this with a 120vac supply and I am using a 6v zener diode. I have connected a 1n4007 across the cap and the resistor as you suggested, but I don't know how to ground the low voltage circuit. I am using the low voltage(6vdc) to power a white LED in a night light circuit. Help! Thanks!
Swagatam said…
Hi Norman, you don't have to connect anything in the indicated area, the ground symbol emphasizes the negative line in all DC circuits....so here too the symbol just signifies the negative common line in the DC section...you can simply ignore this symbol if you wished to.
Norman Kelley said…
Thanks for the quick response! I will build the circuit as soon as the parts arrive. Have a nice day!
lima toshi said…
OK what i have learned so far:lol.... if i connect two extra Z2 and Z3 in series and parallel, will i get 24Volt-@2amp. Thank you.
Swagatam said…
you are partially correct, it will give you 24V, but not 2 amp current, because current level is determined by the input capacitor value.....you can read more on this here

https://homemade-circuits.com/2015/01/calculating-capacitor-current-in.html
lima toshi said…
Ok, so I just have to add extra ppc to get the amperage needed, anyways thanks to you sir, I am learning a lot.
Swagatam said…
yes that's right!!
lima toshi said…
Thank you thank you Swagatam you are the greatest, I was like 50% sure about adding extra ppc but I guessed it right lol but its all because of you sir, I am learning a lot only after I found your great site, wish I had found it sooner but its never too late BTW I never thought I will learn so much in less time, and its all because of great and kind man like you who gives hope to new beginners like me, in what we just loves to spend time on whenever we get time. God bless you sir. Looking forward to learn as much as I can. Keep up the great work, appreciated.
Swagatam said…
You are welcome Lima, keep posting your queries, your involvement will help others also to learn more... keep up the good work...
lima toshi said…
OK, surely i will(: thank you so very much sir, i just love this site... keep up..
David Barner said…
Justin, since this circuit utilizes a full wave bridge rectifier (the 4 diodes in a circle) input polarity is not an issue. All Swagatam was saying is that if you wanted to add a fuse for additional protection, then polarity would be important.
Swagatam said…
Thanks for your understanding David, yes a fuse is not essential for the above circuit since it has a DC output, but for other appliances a fuse must be added to the LIVE line so that in case it blows of no Phase current stays floating within the house electrical.
kirams said…
I don't quite agree completely with this comment. There may not be a difference in the operation of the circuit but if Ground is connected to LIVE/PHASE instead of NEUTRAL, inner circuit becomes vulnerable for electric shock and there is no way to prevent this :(
kirams said…
Swagatam, thank you for your kind responses since 2013 and probably earlier!! Hats off to your consistency. I read through all the responses written on this page.

I came here to find if I can charge Li-Ion battery (The one in dead cell phone) using this circuit and you said it is not possible. But didn't get why it should not work. cell phone battery rating is 3.7v-4.2v. if we configure the circuit to give 5 to 6 v, 50mA would be more than sufficient for charging current, only thing is about auto cut-off. You had suggested cell phone charger circuit for Li-Ion batteries but should I directly connect the Li-Ion battery across 5V SMPS output. This is where I've stuck.

Other interesting note I wanted to tell others is your circuit is used in most cheap chinese mosquito zapper bats. Since it is cheap, it does not have zener diode and instead of capacitor, they have connected battery to be charged. So, I was thinking if I could use Li-Ion battery instead of Lead acid battery that they have.

Sorry, I've asked many questions and comments but please direct me to appropriate threads. and thanks for your help
Swagatam said…
Thank you Kirams, I greatly appreciate your involvement with my site!

Li-Ion cells are costly and highly efficient cells and that's why I don't recommend charging them with the above cheap transformerless type design, where even the mains is not isolated.

It is ofcourse possible to use these power supplies for charging a Li-ion cell but is not advisable.

Li-ion normally accept and work with high current, for quick charging, which the above design may be incapable of delivering therefore the overall feeling is that one should avoid using such crude and dangerous versions of power supplies rather use an SMPS or transformer based designs.

Still if you plan to try it make sure you include the zener diode, otherwise it can become even more dangerous for the cell.
Swagatam said…
The ground connection is a different issue, we are not considering ground here, we are only discussing how the phase/neutral may be used for a given AC load.


The polarity consideration is not critical when the output is DC, just as in the above explained transformerless power supply, but is definitely crucial if an AC appliance is used such as fridge, geyser etc, and also in plug sockets, where the phase must always come through the switch in the socket...

Rajib said…
Dear brother I made this power supply for my LDR light circuit. I made a PCB for that circuit including this power supply and found around 12.5 VDC across the capacitor diode. But the problem is the 12V relay is vibrating and the glow of the light is very low. When the circuit is powered from a separate DC source across the zener diode the circuit works perfect; no vibration. Is there any modification is required to use this power supply? Please advise.
Swagatam said…
Dear Rajib,

you will need to connect another capacitor parallel to C2 with a value around 1000uF/50V, this will solve the issue
Indrawan said…
Dear Mr. Swagatam,
i have a mosquito zapper with 4v lead-acid battery in it. the charger circuit is similar as above, with C1=474 (is it 470nF?), no R2,Z1,and C2.
how to limit the charging voltage to say 4.5-4.6v to keep the battery in float charge range?
thank you.
Swagatam said…
Hi Indravan, you can do that by simply using a 4.6V zener diode for Z1, or alternatively replace Z1 with 8nos of 1N4007 diodes in series, with its cathode towards the ground line side.
Indrawan said…
about the 8-series of 1N4007, does they put in paralel with the battery?
so the anode of 1st-diode connected to batt(+) and the cathode of the last-diode connected to batt(-)?

and does the capacitor C2 is needed for this case?
Swagatam said…
yes that's correct, C2 is optional, but including C2 would allow more average current to the battery and therefore faster charging
Indrawan said…
Dear Mr. Swagatam,
i have put 8-series of 1N4007 in paralel with the battery, and my multimeter reads steady 5.29v at the battery terminals.
would you please help me to understand about the calculation here? why it needs 8-series of diodes and why my multimeter reads 5.29v?

please be patient with me sir, as i am completely newbie in electronics and still have my basic learning curve for it.
Swagatam said…
Hi Indravan, due to its internal characteristics a diode would block around 0.6 to 0.7V and short-circuit the rest of the voltage when its conducting or in the forward biased condition... , which implies that 8 diodes would block 0.6 x 8 = 4.8V...therefore the output would show 4.8V.

In your case it's showing 5.29V which looks quite high, to correct this you can try reducing a couple of diodes in the series and adjust the output to the preferred lower level.
Indrawan said…
it got quite steady as i need with 6-series of diodes.
thank you very much for your kind explanation Sir. :)
Swagatam said…
you are welcome!!
Rajib said…
Dear brother, now its working perfectly. Can I remove capacitor C2 as 1000uF/50V has been added?
Swagatam said…
Hi Rajib, C2 will help to safeguard switch ON surges better, if you want to remove it then make sure to connect an NTC thermistor at the input mains side of the power supply to prevent switch on surge into the connected circuit.
Kesava Raj said…
Hai sir...

Small confusion sir...

I try this circuit using 224 capacitor..and i not use zener and R2..
The output coming 39 to 40v...

My doubt is if i use 12v zener o/p will come 12v means.. remaining 28v what happen sir,,if zener will cause damage or nothing happen...

For eg if o/p coming 150v means if we use 6v zener what happen .o/p will 6v or zener will damage sir...
Is there any limitations voltage to use zener?...pls guide me sir..
Without using R2 we can connect zener or not...R2 is used for voltage drop sir..

Pls tell 224 capacitor current value..

Swagatam said…
Hi Kesava,

the excess volts will get shunted through the zener diode to ground.

the zener voltage has no restrictions, you ca use any.

you can use it without R2.... but R2 is recommended, and it can be lower than 50 ohms...

however if the input capacitor value is above 1uF then higher than 1 watt zener might be required...
Kesava Raj said…
For example if i use more then 3uf to 5uf capacitor. Need to increase zener watts or 1 watts enough.

Thank u sir...
Kesava Raj said…
Instead of using zener we can use voltage regulator like LM7805 & 7812...
Swagatam said…
yes, then you will have to calculate and upgrade the zener power accordingly...yo can calculate the input current from the capacitor through the formulas as explained in the following article

https://homemade-circuits.com/2015/01/calculating-capacitor-current-in.html

Swagatam said…
ICs can be prone to surge currents, and can get damaged, zener diode is more appropriate
Swagatam said…
Charging a cellphone through a capacitive power supply is dangerous and is never recommended...I accidentally failed to notice that you are intending to use it for charging a cellphone...

get an SMPS charger instead..
Swagatam said…
7812 will work!! since it's rated at 1 amp while the input current from the 105/400V is just 50mA...so even if it's 120V or 220V it will be forced to drop down to 12V ultimately....

but again this may be applicable only for ordinary circuits never for charging cellphones.....
Godson said…
Hello sir Swagatam,
I needed a transformerless power supply that can conveniently be used to power an IC and you referred me to this article. Thank you very much sir.
In my application, the circuit will be permanently connected to mains supply, so I need it to be very free from power surge so that the connected components will not damage during operation. What modifications do I need to make in order to achieve this?
Swag said…
Hello Godson, you can use the recommended design as given in the above article, just make sure C1 is selected as per the circuit's current rating, for example if the current consumption of the circuit is 20mA, you can use a 0.33uF for C1 and so on...
amor said…
Hi Sir,
can i use a 10k NTC in place of R2?

and a 474 630vac mylar in place of 105 400vac capacitor?

im using it as a power supply for a 12v relay driver circuit to power a 12v dc motor, can i just also use the same power source for the 12v dc motor?

thanks,
amor
Swag said…
Hi Amor, yes you can try the mentioned components, it should work. If it is a relay that you want to connect at the output, you can eliminate the 12V zener, or use a 24V zener instead. Because a relay is a relatively heavy load and will never burn from a 474 capacitor's surge, therefore the zener diode can be eliminated or a some higher value can be used.
amor said…
Thank you Sir,

how about the 12vdc motor can i just tap it with the same power source? i mean one source to power both relay driver stage and a 12vdc motor load
Swag said…
Amor, If the motor current is within 100mA or 200mA then it might be possible otherwise I won't recommend using a capacitive power supply
amor said…
good day Sir,

Without the 12v zener the output after the rectification will be 310vdc (as mentioned above) if i eliminate the 12v zener i think it is not safe for the relay driver stage to connect in the output Sir.

another thing Sir a dc motor will be connected to the relay output which is also a 12vdc my question is can i just tap the common terminal of the relay in the above power supply?
Swag said…
Amor, a transistor driver stage won't be required here. You can connect the relay coil directly at the output of the transformerless power supply, that's the zener diode would be necessary. If your motor is a low current motor then you can tap the power from the same source otherwise not.
youngking said…
good day sir, thanks for the good work u're doing for man kind. pls can u sugest the kind of transformerless variable power supply circuit i can use to set your circuit i just came across which is twin/split change over circuit because i can't afford transformer type. thanks i will be walting for ur response.
Swag said…
Hi Young king, what is the current requirement of the power supply? if it's over 200mA I won't recommend a capacitive power supply

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