In this post we discuss 4 easy to build, compact simple transformerless power supply circuits. All the circuits presented here are built using capacitive reactance theory for stepping down the input AC mains voltage. All the designs presented here work independently without any transformer, or no transformer.
The Transformerless Power Supply Concept
As the name defines, a transformerless power supply circuit provides a low DC from the mains high voltage AC, without using any form of transformer or inductor.
It 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:
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 shown in the diagram above is a classic design 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 different types of stabilizing stages after the bridge rectifier.
This capacitor grounds instantaneous high voltage surges, thus efficiently safeguarding the associated electronics with it.
How the Circuit Works
The working of this transformless power supply can be understood with the following points:
- 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.
- 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.
- The bridge rectifier rectifies this 220V C to a higher 310V DC, due to the RMS to peak conversion of the AC waveform.
- 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.
- C2 finally filters the 12V DC with ripples, into a relatively clean 12V DC.
1) Basic Transformerless Design
Let's try to understand the function of each of the parts used in the above circuit, in greater details:
- The Capacitor C1 becomes the most important part of the circuit since it is the one that reduces the high current from the 220 V or 120 V mains to the desired lower level, to suit the output DC load. As a rule of thumb every single single microFarad from this capacitor will provide around 50 mA current to the output load. This means, a 2uF will provide 100 mA and so on. If you wish to learn the calculations more precisely you can refer to this article.
- The resistor R1 is used for providing a discharge path for the high voltage capacitor C1 whenever the circuit is unplugged from the mains input. Because, C1 has the ability to store the 220 V mains potential in it when it is detached from the mains, and could risk a high voltage shock to whoever touches the plug pins. R1 quickly discharges the C1 preventing any such mishap.
- Diodes D1---D4 work like a bridge rectifier for converting the low current AC from the C1 capacitor into a low current DC. The capacitor C1 restricts the current to 50 mA but does not restrict the voltage. This implies that the DC at the the output of the bridge rectifier is the peak value of the 220 V AC. This can be calculated as: 220 x 1.41 = 310 V DC approximately. So we have 310 V, 50 mA at the output of the bridge.
- However, the 310V DC may be too high for any low voltage device except a relay. Therefore, an appropriately rated zener diode is used for shunting the 310V Dc into the desired lower value, such as 12 V, 5 V, 24 V etc, depending on the load specs.
- Resistor R2 is used as a current limiting resistor. You may feel, when C1 is already there for limiting the current why do we need the R2. It is because, during the instantaneous power switch ON periods, meaning when the input AC is first applied to the circuit, the capacitor C1 simply acts like a short circuit for a few milliseconds. These few initial milliseconds of the switch ON period, allows the full AC 220 V high current to enter the circuit, which may be enough to destroy the vulnerable DC load at the output. In order to prevent this we introduce R2. However, the better option could be to use an NTC in place of R2.
- The C2 is the filter capacitor, which smoothens the 100 Hz ripples from the rectified bridge to a cleaner DC. Although a high voltage 10uF 250V capacitor is shown in the diagram, you can simply replace it with a 220uF/50V due to the presence of the zener diode.
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.
Example Circuit for LED Decoration Light Application
The following transformerless or capacitive power supply circuit could be used as an LED lamp 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 bulb string having less than 100 LEDs (for 220V input), each LED rated at 20mA, 3.3V 5mm 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........
2) 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 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 310V 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.
You can also use MJE13005 in place of TIP122 for better safety.
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
Using MOSFET Control
The above circuit using emitter follower can be further enhanced by applying a MOSFET source follower power supply, along with a supplemental current control stage using BC547 transistor.
The complete circuit diagram can be seen below:
Video Proof of Surge Protection
3) Zero Crossing Transformerless Power Supply Circuit
The third interesting explains the importance of a zero crossing detection in capacitive transformerless power supplies in order to make it completely safe from the mains switch ON inrush surge currents. The idea was proposed by Mr. Francis.
Technical Specifications
I have been reading about the transformer less power supply articles on your site with great interest and if I am understanding correctly the main problem is the possible in-rush current in the circuit upon switching-on, and this is caused because switching-on does not always occur when the cycle is at zero volts (zero crossing).
I am a novice in electronics and my knowledge and practical experience are very limited, but if the problem can be solved if zero crossing is implemented why not use a zero crossing component to control it such as an Optotriac with zero crossing.
The input side of the Optotriac is low power therefore a low power resistor can be used to lower the mains voltage for Optotiac operation. Therefore no capacitor is used at the Optotriac’s input. The capacitor is connected on the output side which will be switched on by the TRIAC which turns on at zero crossing.
If this is applicable it will also solve high current requirement problems, since the Optotriac in turn can operate another higher current and/or voltage TRIAC without any difficulty. The DC circuit connected to the capacitor should no longer have the in-rush current problem.
It would be nice to know your practical opinion and thank you for reading my mail.
Regards,
Francis
The Design
As rightly pointed out in the above suggestion, an AC input without a zero crossing control can be a major cause of a surge current inrush in capacitive transformerless power supplies.
Today with the advent of sophisticated triac driver opto-isolators, switching an AC mains with zero crossing control is no longer a complex affair, and can be simply implemented using these units.
About MOCxxxx Opto-couplers
The MOC series triac drivers come in the form of optocouplers and are specialists in this regard and can be used with any triac for controlling AC mains through a zero crossing detection and control.
The MOC series triac drivers include MOC3041, MOC3042, MOC3043 etc all these are almost identical with their performance characteristics with only minor differences with their voltage spces, and any of these can be used for the proposed surge control application in capacitive power supplies.
The zero crossing detection and execution are all internally processed in these opto driver units and one has to only configure the power triac with it for witnessing the intended zero crossing controlled firing of the integrated triac circuit.
Before investigating the surge free triac transformerless power supply circuit using a zero crossing control concept let's first understand briefly regarding what's a zero crossing and its involved features.
What is Zero Crossing in AC Mains
We know that an AC mains potential is composed of voltage cycles which rise and fall with changing polarity from zero to maximum and vice versa across the given scale. For example in our 220V mains AC, the voltage switches from 0 to +310V peak) and back to zero, then forwarding downwards from 0 to -310V, and back to zero, this goes on continuously 50 times per second constituting a 50 Hz AC cycle.
When the mains voltage is near its instantaneous peak of the cycle, that is near 220V (for a 220V) mains input, it's in the strongest zone in terms of voltage and current, and if a capacitive power supply happens to be switched ON during this instant, the entire 220V can be expected to break through the power supply and the associated vulnerable DC load. The result could be what we normally witness in such power supply units.... that is instant burning of the connected load.
The above consequence may be commonly seen only in capacitive transformerless power supplies because, capacitors have the characteristics of behaving like a short for a fraction of a second when subjected to a supply voltage, after which it gets charged and adjusts to its correct specified output level
Coming back to the mains zero crossing issue, in a converse situation while the mains is nearing or crossing the zero line of its phase cycle, it can be considered to be in its weakest zone in terms of current and voltage, and any gadget switched ON at this instant can be expected to be entirely safe and free from a surge inrush.
Therefore if a capacitive power supply is switched ON in situations when the AC input is passing through its phase zero, we can expect the output from the power supply to be safe and void of a surge current.
How it Works
The circuit shown above utilizes a triac optoisolator driver MOC3041, and is configured in such a way that whenever power is switched ON, it fires and initiates the connected triac only during the first zero crossing of the AC phase, and then keeps the AC switched ON normally for rest of the period until power is switched OFF and switched ON again.
Referring to the figure we can see how the tiny 6-pin MOC 3041 IC is connected with a triac for executing the procedures.
The input to the triac is applied through a high voltage, current limiting capacitor 105/400V, the load can be seen attached to the other end of the supply via a bridge rectifier configuration for achieving a pure DC to the intended load which could an LED.
How Surge Current is Controlled
Whenever power is switched ON, initially the triac stays switched OFF (due to an absence of the gate drive) and so does the load connected to the bridge network.
A feed voltage derived from the output of the 105/400V capacitor reaches the internal IR LED through the pin1/2 of the opto IC. This input is monitored and processed internally with reference to the LED IR light response.... and as soon the fed AC cycle is detected reaching the zero crossing point, an internal switch instantly toggles and fires the triac and keeps the system switched ON for the rest of the period until the unit is switched OFF and ON yet again.
With the above set up, whenever power is switched ON, the MOC opto isolator triac makes sure that the triac is initiated only during that period when the AC mains is crossing the zero line of its phase, which in turn keeps the load perfectly safe and free from the dangerous surge in rush.
Improving the above Design
A comprehensive capacitive power supply circuit having a zero crossing detector, a surge suppressor and voltage regulator is discussed here, the idea was was submitted by Mr. Chamy
Designing an Improved Capacitive Power Supply Circuit with Zero Crossing Detection
Hello Swagatam.
This is my zero crossing, surge protected capacitive power supply design with voltage stabilizer,i will try to list all of my doubts.
(I know this will be expensive for the capacitors,but this is only for testing purposes)
1-I'm not sure if the BT136 haves to be changed for a BTA06 for accommodating more current.
2-The Q1 (TIP31C) can handle only 100V Max. Maybe it should be changed for a 200V 2-3A transistor?,like the 2SC4381.
3-R6 (200R 5W),I know this resistor is pretty small and its my
fault,i actually wanted to put a 1k resistor.But with an 200R 5W
resistor it would work?
4-Some resistors have been changed following your recommendations to make it 110V capable.Maybe the 10K one needs to be smaller?
If you know how to make it work correctly,i will be very happy to correct it.If it works i can make a PCB for it and you could publish it in your page (For free of course).
Thank you for taking the time and viewing my full of faults circuit.
Have a nice day.
Chamy
Assessing the The Design
Hello Chamy,
your circuit looks OK to me. Here are the answers to your questions:
1) yes BT136 should be replaced with a higher rated triac.
2)TIP31 should be replaced with a Darlington transistor such as TIP142 etc otherwise it might not work properly.
3) when a Darlington is used the base resistor could be high in value, may be a 1K/2 watt resistor would be quite OK.
However the design by itself looks like an overkill, a much simpler version can be seen below https://homemade-circuits.com/2016/07/scr-shunt-for-protecting-capacitive-led.html
Regards
Swagatam
Reference:
4) Switching Transformerless Power Supply using IC 555
This 4rth simple yet smart solution is implemented here using IC 555 in its monostable mode to control in rush surge in a transfomerless power supply via a zero crossing switching circuit concept, wherein the input power from the mains is allowed to enter the circuit only during the zero crossings of the AC signal, thereby eliminating the possibility of surge inrushes. The idea was suggested by one of the avid readers of this blog.
Technical Specifications
Would a zero cross transformerless circuit work to prevent the initial inrush current by not allowing turn on until the 0 point in the 60/50 hertz cycle?
Many solid state relays which are cheap, less then INR 10.00 and have this ability built in them.
Also I would like to drive 20watt leds with this design but am unsure how much current or how hot capacitors will get I suppose it depends on how the leds are wired series or parallel, but lets say the capacitor is sized for 5 amps or 125uf will the capacitor heat up and blow???
How does one read capacitor specs to determine how much energy they can dissipate.
The above request prompted me to look for a related design incorporating a IC 555 based zero crossing switching concept, and came across the following excellent transformerless power supply circuit which could be used for convincingly eliminating all possible chances of surge inrush.
What's a Zero Crossing Switching:
It's important to learn this concept first before investigating the proposed surge free transformerless circuit.
We all know how a sine wave of an AC mains signal looks like. We know that this sine signal starts from a zero potential mark, and exponentially or gradually rises to the peak voltage (220 or 120) point, and from there exponentially reverts to the zero potential mark.
After this positive cycle, the waveform dips and repeats the above cycle but in the negative direction until it comes back yet again to the zero mark.
The above operation happens about 50 to 60 times per second depending upon the mains utility specs.
Since this waveform is what enters the circuit, any point in the waveform other than the zero, presents a potential danger of a switch ON surge due to the involved high current in the waveform.
However the above situation can be avoided if the load confronts the switch ON during the zero crossing, after which the rise being exponential doesn't pose any threat to the load.
This is exactly what we have tried to implement in the proposed circuit.
Circuit Operation
Referring to the circuit diagram below, the 4 1N4007 diodes form standard bridge rectifiers configuration, the cathode junction produces a 100Hz ripple across the line.
The above 100Hz frequency is dropped using a potential divider (47k/20K) and applied to the positive rail of the IC555. Across this line the potential is appropriately regulated and filtered using D1 and C1.
The above potential is also applied to the base Q1 via the 100k resistor.
The IC 555 is configured as an monostable MV which means its output will go high every time its pin#2 is grounded.
For the periods during which the AC mains is above (+)0.6V, Q1 stays switched OFF, but as soon as the AC waveform touches the zero mark, that is reaches below the (+)0.6 V, Q1 switches ON grounding pin#2 of the IC and rendering a positive output of the IC pin#3.
The output of the IC switches ON the SCR and the load and keeps it switched ON until the MMV timing elapses, to begin a new cycle.
The ON time of the monostable can be set by varying the 1M preset.
Greater ON time ensures more current to the load, making it brighter if it's an LED, and vice versa.
The switch ON conditions of this IC 555 based transformerless power supply circuit is thus restricted only when the AC is near zero, which in turn ensures no surge voltage each time the load or the circuit is switched ON.
Circuit Diagram
For LED Driver Application
If you are looking for a transformerless power supply for LED driver application at commercial level, then probably you can try the concepts explained here.
Hi
In the case of a power supply for a few milliamps and using a limiting resistor of appropriate value in series with the capacitor, in order to limit the peak current to 1 ampere (max surge current of moc), could we eliminate the triac using only the moc? Thank you
Hi, yes that’s possible.
using transformerless power supply my rtc get reset unfortunately. i have used MCP7940 RTC
please use SMPS then.
Hi, Could you please tell me the wattage rating for resistors 360, 39 and 330 ohms which are used in MOC3041?
And How to calculate the Rin for MOC3041 ? Because am not able to understand from the datasheet.
Hi, all resistors are 1/4 watt 5%, the Rin can be calculated using standard LED formula:
Rin = Supply input – LED fwd voltage / LED current
wattage = Supply input – LED fwd voltage x LED current
Hello again,
I have a general question about Mosfets;
can we use couple of mosfets with same voltage rating and different current(mean Vds, Ids, Vgs) paralell together in a circuit?
Yes you can do that!
Thanks
Is it possible to use mosfet type power supply to run a high amp consumer, like 5Amp, 12Vdc motor? If so what changes have to be made?
It is possible but if the input/output difference is large, then the Mosfet will become very hot and waste a lot of power.
Hello Swag,
I made the first circuit and uses 7812 regulator but the zener(15v, 1w) and regulator got broke both. I know that the transformer is the ideal appraoch but i need a 12vdc transformerless power supply. Is there any reliable circuit for 12vdc? Something which does not affect the rest of circuit in the case of failure?
Hello Mah, the MOSFET version is the most reliable and is safe from switch ON surges.
Dear Swagatam, nice ideas and circuits you have given here, ut I want to share my thoughts and want your opinion too… introducing optoisolator or 555 IC will also increase the complexity or atleast the circuit will need more space… then why shouldn’t I use the transformer which eliminates all issues and also provides isolation from mains…
Hello Asif, iron core transformer is the best option if weight and space are not a matter of concern to the user.
Hello again Swagatam,
Is it possible to use the first circuit as 12vdc source to feed 555 ic in PWM controller?
I dont want to use a 12v transformer for the application.
If you have any suggestion, kindly refer it to me.
Thanks
Hi Mah,
yes you can if the deadly floating mains AC around the whole circuit is not a concern to you. For your application you can reduce the 105/400V to 474/400V.
Hi Swagatam! Thanks for your help on these circuits. But then I really need your help on this;
Am building a large power supply to power up a large building based on batteries. The battery bank capacity can go as high as 110V/400AH and 48V/1000AH. Charging up these large battery bank is a bit of a problem, I have already built an automatic charger and battery to load control and am currently customizing an SMPS from one of the circuit you posted (0-100v 0-100A variable power supply) which I believed will work perfectly. But I need a transformerless 230Vac mains to dc supply for the SMPS. How can I calibrate this circuit to be able to obtain an adjustable 120V/100Amps? Suitable for the SMPS. I believe stacking up the capacitor to about 2200uf/400v can obtain up to 100A? If am right, pls I need your prescription. Thanks
Hi Ben, yes that may be possible. You can try the idea with the “MOSFET control” design….but make sure the MOSFET is rated to handle a minimum of 150V at 200 amps
Hi Swagatam,
I would like to use your Simple Transformerless Power Supply to replace a (60HZ hum) switching power supply for a radio.
Can you provide the component value changes that would must be made for optimum performance on 120V AC input and provide 6.0V DC at 0.5A output?
Thanks
Hi Tony, you can try the “MOSFET control” design, and eliminate the T2, R2 from the circuit.
After adjusting 6V at the output through the given pot, glue the pot so that the 6 V does get disturbed in future.
After this, connect a 6800uF/ 25V capacitor across this 6V output DC to ensure there’s no hum involved in the DC.
Hi Swagatam,
Thanks for your timely response. Should I also change D2 to a 6V Zener Diode?
Hi Anthony, no need to change the zener value, it should be a 12 V zener only.
Hi sir. Can I increase c1 to be able to charge 12v battery
Miracle, a capacitive power supply cannot be used for charging a lead acid battery.
But, In Flashlights, they use it, so why not?
for small batts it will work, not for bigger batteries
Please guide me for a transformerless supply 3.3V with zener diodes
Please Use 3.3V 1 watt zener diode for Z1
Hi sir , I want to make an Aquarium Led Light, is this applicable?
Hi Reafe, you can use it if the LEDs are not in contact with the water in any manner, because the entire circuit is attached with the AC mains and is fully prone to electric shock…
How many LED maximum sir?
I want to try the #1 Basic Transformerless
If you remove the zener then dividing the supply output from the diode with the LED forward voltage will give you the total number that can accommodate.
For example if the DC is 310V and the LED forward voltage is 3.3V then 310 / 3.3 = 93 LEDs approximately in series.
Requires brain to understand 🙂 Borrow a little from somewhere then may be you’ll start understanding.
Hello dear swagatam!
Please I am having this issues with transformerless power supply; “Each time I intend to use transformerless power supply to power microcontroller 8051, atmega328P and even a DC FAN of 12V, 1.4A, I notice that they never get powered even though the power supply has been tested to produce the required 12v or 5v dc as the case may be. If I read the output of the power supply after I have connected the load say 12v, 1.4A DC FAN, I noticed that the voltage dropped further to 2.4vdc which of course never powers the FAN.” So Please help me in this case. What might be the reason for the further voltage dropping? and how can I prevent it from happening. In the design, I used 105, 400V capacitor at the input stage to drop the current and 12V zener for output stabilization. just like the first circuit in this page.
Hello Kingsley, the 105 capacitor will produce only 60mA so it cannot be used to handle 1 amp current load.
By the way a capacitive power supply is never recommended for microcontrollers or any sensitive electronic circuit.
OK, Thank You boss.
Please I need your help sir.
Is their any circuit you can recommend me to use in handling high voltage supply apart from stabilizer? The problem I am having is this, I designed an inverter that powers my clients house; but their mains voltage supply sometimes go very high up to 315VAC, and this usually burns the MOSFETs each time the inverter is in charging mode and the small changeover transformer (12V, 500mA) also gets burnt too. But when the voltage supply is normal between 220VAC to 240VAC, the inverter charges and the charger switches off when the batteries are fully charged.
Therefore, I was trying to use the transformerless power supply system to correct the issue in such a way that i have written a program in C language that will read the AC voltage level from the mains supply and which will automatically turn off the inverter charger whenever the voltage supply goes up beyond 240VAC. I thought of using the transformerless counterpart since the changeover transformer also gets affected too. But now that you said that transformerless/capacitive power supply is not recommended for microcontrollers, what can i do to stop this regular damage of my MOSFET and changeover transformer?
Please sir your help is highly recommended and a good circuit will be very, very appreciated.
Thank you in anticipation of your positive response.
Hi Kingsley,
In that case you can apply the following capacitive power supply:
https://www.homemade-circuits.com/wp-content/uploads/2019/05/100-watt-LED-bulb-improved-design-1.png
But remember these are not isolated from mains so everything in the inverter will be at 220V mains potential, even the battery terminals.
Sorry I observed a typographic error in the first statements. Please kindly used this one.
Good morning dear Swagatam. I sincerely appreciate your swift response to my many questions; Thank You for being always available to help resolve my circuit difficulties.
Now, looking at the circuit you suggested for me, the AC (Mains) supply terminated at the bridge rectifier as usual right? and If carefully handled, it will remain within there! The only point where the inverter circuit and battery get connected with the suggested circuit is their common ground (GND) i hope, right? But you also pointed out that “these are not isolated from mains so everything in the inverter will be at 220V mains potential, even the battery terminals” please kindly explain that part more so I can be cleared before trying to implement this circuit with the existing predicament.
i also implore you sir to help me with a surge protector circuit up to 30A that can work as a high voltage monitor just like conventional surge protector in the market that trips off if mains supply voltage is too high; maybe that would be better alternative than the capacitive power supply since the capacitive counterpart may result in huge damage.
Thank you sir as you respond to me, God bless you.
Hello Kingsley, yes due to the common ground the 220V from the capactive power supply can easily reach the battery terminals, there’s no way to prevent this.
Another alternative can be to use two 12V/500mA 220V transformer and tie their 220V wires in series. This will ensure the transformers can withstand 700V peak inputs. The secondary sides could be configured with separate bridge rectifiers and filter capacitor. The output from the bridge can be connected in series to get the required safe DC.
For the high voltage protector concept you an refer to this post:
https://www.homemade-circuits.com/highly-accurate-mains-high-and-low/
Ok, Thank you for your answers. You are too much sir. I will try the double transformer counterpart.
thanks a lot.
No problem!
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
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…
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…..
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..
Instead of using zener we can use voltage regulator like LM7805 & 7812…
ICs can be prone to surge currents, and can get damaged, zener diode is more appropriate
For example if i use more then 3uf to 5uf capacitor. Need to increase zener watts or 1 watts enough.
Thank u sir…
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
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…
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.
it got quite steady as i need with 6-series of diodes.
thank you very much for your kind explanation Sir. 🙂
you are welcome!!
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
Dear brother, now its working perfectly. Can I remove capacitor C2 as 1000uF/50V has been added?
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.
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.
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.
You are welcome Lima, keep posting your queries, your involvement will help others also to learn more… keep up the good work…
OK, surely i will(: thank you so very much sir, i just love this site… keep up..
Ok, so I just have to add extra ppc to get the amperage needed, anyways thanks to you sir, I am learning a lot.
yes that's right!!
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.
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
Thanks for the quick response! I will build the circuit as soon as the parts arrive. Have a nice day!
OK thanks!
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.
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 ?
NO, unless and until the input AC drops below the zener voltage value
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
Hi Davis, you can use the same circuit for 220V as well as 240V.
3 watt LED will not work with this circuit.
Sir I want to make an rechargeable 12v emergency light with battery level indicator without transformer plz help me
waqas, similar circuits are already present in this website please search it through the given search boxes…
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
Sir can I use this circuit to power your egg incubator thermostat circuit.
no you can't, either an SMPS adapter or a transformer based power supply can be used and is recommended.
can i change the polarity of input(Line and N)?
yes you can!
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
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.
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
I want 12v/300ma transformer less power supply circuit diagram please send link sir
https://homemade-circuits.com/2014/02/simple-1-watt-to-12-watt-smps-led.html
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.
R2 is NTC for inrush current or power resistor?
R2 is an ordinary resistor but you can definitely replace it with a suitable NTC
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.
i need a transformerless in this conditions: 6V at 120VAC and 12V at 220VAC! have you circuit for this ?
just change the zener value accordingly in the above shown design…that's all is neeeded
hai friend…how can i do my project of mobile charge sharging transfromerless+
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
please sir tell me , i want 220v ac to 60v dc transformerless circuit without transistor
you can use the above shown circuit and replace the zener with a 60V zener
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?
Harvest, no it's not recommended and might not work….use a 12V ad to dc SMPS adapter or a transformer power supply
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.?
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
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?
It means your capacitor is faulty…you can try 7812 IC
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.
hello sir
i am tring to make supply from 220v ac to 72 v dc with 2ampere
could u please help me in it
sorry I do not have this circuit at the moment…
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.
Sir good work. But what is the use of r2 50ohm 1w resistor. Can I use 100ohm resistor instead of this. Plz replay me.
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
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
sir can u help me to convert 230v ac to 110v ac …step down circuit
Please help me.Can I use 2uF/400V for C1?
1uF/400V is not available near my area.
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
Can I use this circuit to power 12v computer Fan?
yes, but at a slower speed…
What should i do to maximize the speed of the fan?
add anther capacitor parallel with C1
Thank you Swagatam.. Can you give the modified circuit? Just to make sure that I make this right.
My pleasure pakol, make C1 = 2uF/400V that's all, and preferably use a 12V 2 watt zener.
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
capacitor steps down the current not the voltage…voltage is controlled by the zener diode
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
For wat purpose the circuit can be used for……….
for powering any DC circuit below 50ma
can you please explain the function of R1 and C1 ?
i mean why they are in parallel ?
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
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
you can try the circuit discussed in the above article….use a 5V zener at Z1, and 0.33uF/400V for C1
there isn`t 50 ohm/1w resisiton to find then what can i use to that?
the value is not critical, you can try other values such 33, 47 68, ohm etc.
why the 50ohm 1watt resistor is very hot?
It is not a calculated value, it’s only to prevent surge current to the load. You can reduce it to 20 ohms and check the difference.
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.
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.
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
Yes it's possible, I'll try to address it soon in my blog
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.
R1 will be always 1/4 watt
Have u made it?
my friend said we can't put resistor facing 220 volt AC
a resistor can be inserted anywhere in a circuit for suppressing surge, the position is never critical.
Sir. Plz give ac oprated mobile battery li – ion batt circuit
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
No, it won't charge Li-ion batt
oh thanks a lot dear
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.
sure Pete! thanks, my pleasure:)
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.
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.
Sir
I made this circuit but sum time after r2 is burn
Help me
Jagdish, use 474/400V in place of 105/400V
Hello Swagatam Majumdar.. How can I make the output of this power supply be 12V 1A?
hello Jason, getting current above 100mA is not recommended for capacitive power supplies…because it could dangerous for the connected load under those specs.
Hi Fazal, yes you can use a 5V zener to get a 5V output from this circuit.
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
Do you have a 12V 1A transformerless? Or 2A
presently i don't have it.
50mA
How much AMPERE is this 12V transformerless,?
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
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.
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.
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.
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.
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…
No, it isn't.
Hi Swagatam
Is it possible to have current in between 100mA and 200mA?
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.
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.