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How to Make a Simple Transformerless Power Supply Circuit

How to Make a Simple Transformerless Power Supply Circuit

A very compact simple transformerless power supply circuit is explained here can be built 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:

105/400V capacitor 1uF 400V capacitor for transformerless power supply

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.
Simple Transformerless Power Supply Circuit

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.

transformerless power supply PCB layout

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:

capacitive LED driver circuit for strips

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........

Upgrading to Voltage Stabilized Transformerless Power Supply

Now let's see how an ordinary capacitive power supply may be transformed into a surge free voltage stabilized or variable voltage transformerless power supply applicable for almost all standard electronic loads and circuits. The idea was requested by Mr. Chandan Maity.

Technical Specifications

If you remember, I communicated you sometime before with comments at your blog.

The Transformerless circuits are really good and I tested couple of those and running 20W, 30W LED.Now, I am trying to add some  controller, FAN and LED all together , hence, I need a dual supply.

The rough specification is:

Current rating 300 mAP1= 3.3-5V 300mA ( for controller etc)P2=  12-40V (or higher range), 300mA (for LED)
I thought to use your 2nd circuit as mentionedhttps://homemade-circuits.com/2012/08/high-current-transformerless-power.html

But, I am not able to freeze the way how to get 3.3V without using extra capacitor. 1. Can, a second circuit may be placed from the output of first one? 2. Or, a second TRIAC, bridge to be placed in parallel with first one, after capacitor to get 3.3-5V

I shall be glad if you kindly help.

Thanks,

The Design

The function of  the various components used across the various stages of the above shown voltage controlled transformerless power supply circuit may be understood from the following points:

The mains voltage is rectified by the four 1N4007 diodes and filtered by the 10uF/400V capacitor.

The output across the 10uF/400V now reaches around 330V which is the peak rectified voltage achieved from the mains.

The voltage divider network configured at the base of the TIP122 makes sure that this voltage is reduced to the expected level or as required across the power supply output.

If a 12V is required the 10K pot may be set to achieve this across the emitter/ground of the TIP122.

The 220uF/50V capacitor ensures that during switch ON the base is rendered a momentary zero voltage in order to keep it switched OFF and safe from the initial surge in-rush.

The inductor further ensures that during the switch ON period the coil offers a high resistance and stops any inrush current to get inside the circuit, preventing a possible damage to the circuit.

For achieving a 5V or any other attached stepped down voltage, a voltage regulator such as the shown 7805 IC may be used for achieving the same.

Circuit Diagram

SHARING IS CARING!


About the Author

I am an electronic engineer (dipIETE ), hobbyist, inventor, schematic/PCB designer, manufacturer. I am also the founder of the website: https://www.homemade-circuits.com/, where I love sharing my innovative circuit ideas and tutorials. If you have any circuit related query, you may interact through comments, I'll be most happy to help!



154 thoughts on “How to Make a Simple Transformerless Power Supply Circuit”


  1. Howdy, Friend! Interested to Learn Circuit Designing? Let's Start Discussing below!
  2. 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.

    • 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

  3. 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?

    • 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…

  4. 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…..

  5. 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..

  6. For example if i use more then 3uf to 5uf capacitor. Need to increase zener watts or 1 watts enough.

    Thank u sir…

  7. 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..

    • 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…

  8. 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.

    • 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.

    • 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?

    • yes that's correct, C2 is optional, but including C2 would allow more average current to the battery and therefore faster charging

    • 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.

    • 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.

  9. 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.

    • Dear Rajib,

      you will need to connect another capacitor parallel to C2 with a value around 1000uF/50V, this will solve the issue

    • 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.

  10. 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

    • 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.

  11. 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.

  12. 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.

  13. 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!

    • 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.

  14. 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 ?

  15. 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

  16. Sir ,thanks for your previous reply. Can you please recommend me any of your circuits without transformer suit able for the incubator circuit.

    • 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

  17. 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????

    • 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

  18. 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.

  19. 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.

    • 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.

      • 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

        • 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.

          • 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

            • 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

          • 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?

            • 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.

  20. 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?

  21. 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.?

  22. 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..?

    • 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.

    • 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 1000µ (or more)/100V capacitor to get 72VDC.

    • 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

  23. 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

    • 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

  24. 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

  25. 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)

    • 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

    • 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

    • 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.

  26. 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

  27. 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.

    • 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.

  28. 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

  29. 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.

    • 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.

  30. 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?

    • you can use the same circuit with 120V also, the output result from transformerless supply would be the same as for 220V.

    • hello Jason, getting current above 100mA is not recommended for capacitive power supplies…because it could dangerous for the connected load under those specs.

  31. 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

    • 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

  32. 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?

    • 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.

  33. 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.

    • 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.

    • 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.

  34. 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?

    • 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.

  35. 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?

    • 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.

  36. 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

    • 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.

    • 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 🙁

    • 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…

    • 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.

  37. 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.

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