The simple configuration of a transformerless power supply circuit presented below is able to provide high current at any assigned fixed voltage level. The idea seems to have solved the problem of deriving high current from capacitive power supplies which earlier seemed a difficult proposition. I assume I am the first person to have invented this.
Introduction
I have discussed a few transformerless power supply circuits in this blog which are good only with low power applications, and tend to become less effective or useless with high current loads.
The above concept utilizes high voltage PP capacitors for dropping the mains voltage to the required level, however it is unable to raise current levels as per any desired particular application.
Although, since the current is directly proportional to the reactance of the capacitors, means the current can be lifted just by incorporating more capacitors in parallel. But this puts a risk of high initial surge currents which might destroy the involved electronic circuit instantly.
Adding Capacitors to Increase Current
Therefore adding capacitors might help to increase the current specs of such power supplies but the surge factor must be first taken care of for making the circuit feasible for practical usage.
The circuit of a high current transformerless power supply explained here hopefully, effectively handles the surge developing from power transients such that the output becomes free from the dangers, and provides the required current supply at the rated voltage levels.
Everything in the circuit is kept just as its old counterpart, barring the inclusion of the triac and zener network which actually is a crowbar network, used for grounding anything that goes above the rated voltage.
In this circuit the output would hopefully provide a stable voltage of around 12+ volts at around 500 mA of current without the dangers of any accidental voltage or current influx.
CAUTION: THE CIRCUIT IS NOT ISOLATED FROM MAINS AND THEREFORE INVOLVES HIGH RISK OF ELECTROCUTION, APPROPRIATE PRECAUTION NEEDS TO BE EXERCISED.
UPDATE: A better and a more advanced design can be learned in this zero crossing controlled surge free transformerless power supply circuit
Parts List
- R1 = 1M, 1/4W
- R2,R3 = 1K, 1/4 WATT
- C1----C5 = 2uF/400V PPC, EACH
- C6 = 100uF/25V
- All DIODES = 1N4007
- Z1 = 15V, 1 watt
- TRIAC = BT136
A neatly drawn PCB for the above high current transformerless power supply may be seen below, it was designed by Mr. Patrick Bruyn, one of the avid followers of this blog.
Update
A deeper analysis of the circuit showed that the triac was dumping a significant amount of current while restricting the surge and controlling the current.
The approach taken in the above circuit for controlling voltage and the surge is negative in terms of efficiency.
In order to obtain the intended results as proposed in the above design and without shunting precious amps, a circuit with exactly opposite response needs to be implemented, as shown above
Interestingly, here the triac is not configured to dump power rather it's wired in a such a way that it switches OFF power as soon as the output reaches the specified safe voltage limit, which is detected by the BJT stage.
New Update:
In the above modified design the triac may not conduct properly due to its rather awkward positioning. The following diagram suggests a correctly configured version of the above, which can be expected to operate as per the expectations. In this design we have incorporated an SCR instead of a triac since the positioning of the device is after the bridge rectifier and therefore the input is in the form of a DC ripples and not AC.
Improving the above design:
In the above SCR based transformerless power supply circuit, the output is surge protected through the SCR, but the BC546 is not protected. In order to ensure a complete protection for the entire circuit along with the BC546 driver stage, a separate low power triggering stage needs to be added to the B546 stage. The amended design can be seen below:
The above design can be further improved by modifying the position of the SCR as shown below:
So far we studied a few transformerless power supply designs with high current specs, and also have learned regarding their different modes of configurations.
Below we would go a little farther and learn how to make a variable version circuit using an SCR. The explained design not only provides the option of getting a continuously variable output but is also surge protected, and therefore become much reliable with its intended functions.
The circuit can be understood from the following description:
Circuit Operation
The left side section of the circuit is quite familiar to us, the input capacitor along with the four diodes and the filter capacitor forms the parts of a common, unreliable fixed voltage transformerless power supply circuit.
The output from this section will be unstable, prone to surge currents, and relatively dangerous to operate sensitive electronic circuits.
The portion of the circuit on the right side of the fuse transforms it into a completely new, sophisticated design.
The Crowbar Network
It's in fact a crowbar network, introduced for some interesting functions.
The zener diode along with R1 and P1 forms a kind of voltage clamp which decides at what voltage level the SCR should fire.
P1 effectively varies the zener voltage from zero to its maximum rating, so here it an be assumed to be zero to 24V.
Depending upon this adjustment, the firing voltage of the SCR gets set.
Supposing P1 sets a 12V range for the SCR gate, as soon as mains power is switched ON, the rectified DC voltage starts developing across D1 and P1.
The moment it reaches the 12V mark, the SCR gets sufficient triggering voltage and instantly conducts, short circuiting the output terminals.
The short circuiting of the output tends to drop the voltage toward zero, however the moment the voltage drop goes below the set 12V mark, the SCR is inhibited from the required gate voltage and it reverts to it non conducting state.... the situation yet again allows the voltage to rise, and the SCR repeats the process making sure the voltage never goes above the set threshold.
The inclusion of the crowbar design also ensures a surge free output since the SCR never allows any surge to pass through to the output under all circumstances, and also allows relatively higher current operations.
Circuit Diagram
Another SCR based Circuit
This SCR based high current Transformerless Power Supply consists of rather a few, easily accessible electronic parts. The output voltage level (and also the level of feasible current as provided in the Table I) is adjustable by rotating the rotary switch S1.
Table#1
Zero Crossing Controlled High Current Transformerless Power Supply Circuit
The following circuit shows how a zero crossing concept can be implemented to create an effective transformerless high current power supply circuit, which is highly customizable.
Advantages of this Circuit are as follows:
100% surge free ensures that the load, zener diode and the capacitor are completely safe all the time regardless of the input switching conditions of the power supply.
No heat dissipation ensures that the circuit's efficiency is maximum.
How the Circuit Works
We know that the main issue with transformerless power supply circuit is the switch ON surge current, which happens due to the sudden peak AC entering the electronic circuit connected with the power supply.
This sudden in-rush voltage and current leads to the burning of the vulnerable electronic components attached with the power supply.
This means that, if the load is allowed to be switched ON whenever the AC waveform nears the zero crossing then such mishaps can be avoided.
The above circuit does exactly this.
The PNP TIP127 conducts only when the AC waveform is below the zener value.
When the TIP127 conducts the AC waveform is already within the safe range of the load and this safe voltage gets stored in the 1000uF capacitor for powering the load.
The process continues for each cycle and only when the AC peak has dropped down safely to the zener value, which keeps the load powered consistently, with an optimized voltage and current inputs.
Hi Swagatam!
I must say these articles are very helpful.
I needed your opinion on the following idea for building a high current transformer less power supply.
We design it in two stages. The first stage, is a low current stage which just generates enough power for a small, low-cost, microcontroller with an ADC.
In the second stage, this microcontroller using the ADC and a MOSFET … samples the input AC and disconnects the AC as soon as the voltage goes above say Xvolts and below 0V. So the AC waveform gets clipped and rectified at Xvolts positive to 0V. Then we use a smoothing capacitor to generate the DC we want by changing the value of X in the firmware.
Since the MOSFET is controlled by the microcontroller… it is never switched on above Xvolts … so the surge etc. are all handled adequately.
The point is .. one MOSFET that can handle, say, 200mA of current at 300V, and a small microcontroller are still much cheaper (and easily available) compared to components needed in a high-performance SMPS power supply.
I built and tested this circuit and it works … I am just wondering why it is not used so widely.
Thank you Vineet,
May I know what is the current and voltage outputs of the concept that you built? Can you build a 12 V, 5 amp design using your concept. So that is the actual challenge, building a high current low voltage power supply without involving a transformer.
Let me know your thoughts on this.
I earlier designed two power supplies using flyback switched mode transformer based power supplies for two different projects …
48V 2A for a telecom product4V 600mA for a metering productAt that time I did not focus too much on making them tranformer-less … but while I was validating these designs, I played around with the concept I discussed and it worked. However, I did not invest too much serious time on it then.
Now I need to mass-produce another product and I am seriously looking at using the concept I proposed. But needed your opinion on this before I start allocating resources to it. Can you think of any reason it would not work … so I can think of some way to design better before I ask my team to start prototyping.
The mosfet would turn on when the AC voltage is just zero crossing towards positive, so there would be no stress. There could be some risk that the mosfet would disconnect at X voltage …(say 12V) … but I think since we are using a 300V mosfet … it should not have a problem handling that.
Your proposed concept is supposed to work using a microcontroller and without a transformer. However without a transformer high current generation may not be possible? If you think generating high current is possible, I would be interested to know. According to me SMPS is the only way to transform high AC voltage to a low DC voltage with the desired high current, efficiently.
friend swagatam, I need a transformerless with a stable voltage output of 36 volts dc and amperes 1.5 amperes (in actual implementation it is only 495 milli amperes), is there a diagram above that I can apply?, and what components should I replace in the diagram above so that it can work I can use it, thanks for your attention.
Hi Sudarsono, you can perhaps try the following design:
https://www.homemade-circuits.com/wp-content/uploads/2013/05/surge-free-transformerless-power-supply-circuit-1.png
You can replace the 24V zener with a 36 V 1 watt zener diode and the 220 ohm resistor with a 1K 5 watt resistor. The SCR can be any 5 amp 400 V SCR. The capacitor on the mains AC side can be a 30uF/400V non-polar capacitor. However remember the SCR will get quite hot, that is the drawback of this kind of design.
how to overcome so that the scr is not too hot or becomes hot, thank you for the help, friend swagatam
The heat will depend on the input voltage and the output voltage difference. Since there’s a big difference between 36 V and 220 V, the heat will be also very high, there’s no way to reduce it.
Oky sir,
would you please help me with SMPS circuit which can output 12v at 20amps?
i, have freezing fridge which its power supply was burnt.
Godwin, I do not have a 12V 20 amp SMPS circuit. However, a 20 amp SMPS can be hugely complicated to build at home, so i would recommend you to buy it online which can be quite cheap and extremely efficient.
oky sir,
i, should explain it properly in this way;
as i keep it in mind, a transformerless produces a very low current in (milliamperes) not amperes. What i want is to modefy the circuit to drive 12v 20 amps loads purposes. If you can help this circuit, please present it to me immediately.
thanks,
Godwin.
Sure I understand, however 20 amp is actually too high. I wouldn’t recommend even 1 amp, because even at 1 amp the triac or the SCR can heat up a lot. SMPS is the best way to get a high amp output with max efficiency.
Oky sir,
by ignoring the relay at the ouput of the transformerless, should it be modefied by replacing the STTH600CW rectifier diode along with an inductor?
Godwin.
Hi Godwin,
sorry I could not understand how would you replace the relay with a STTH600CW diode and a coil, and for what for purpose?
Hi swagatam,
i thank you very much, for the work done day and night providing helpfull different circuits. I, Godwin, have benefit from these learning articles keep it on. Now coming to the topic; transformerless with high output current.
sir, my question is, is it possible to include a relay inorder to have high current?(2) and how? If yes, what are the cautions to this? Best regards
Godwin Shonga.
malawi.
Thank you Godwin,
I wouldn’t recommend more than 500 mA in a transformerless power supply circuit. Yes you can use a relay to switch a capacitive power supply as shown in the following example circuit:
https://www.homemade-circuits.com/wp-content/uploads/2022/02/capacitive-LED-driver-with-relay-for-preventing-switch-ON-surge.jpg
hello, i just want to know what the circuit would be for a 230vac to 60dc 10A power inverter in the same way as shown in the design pictures?
Hello, A capacitive concept cannot be used for currents over 200 mA. So for a 10 amp current you might need an SMPS circuit.
Hello Swagatam,
What do you mean by a SMPS circuit please?
The power supply has to be like and function as a transformer and need to be continious.
Like an IGBT welding machine but less complicated.
Hello Willem,
An SMPS is a switched mode power supply, as shown in the following images:
https://www.homemade-circuits.com/wp-content/uploads/2018/06/smps-flyback-design.jpg
Hi there
My Black & Decker heat gun just stop working and uses a seemingly simple 220V AC board to power a 12V DC (0.284A) motor for blowing the air and activate the heater. So far I have tested the triac and some other parts seems in working order. Could I email the picture of the circuit board so you might advise what component could be faulty.
Thanks
Hi, You can email me, I will try to solve it for you.
Hi Swagatam,
On the Crowbar Network, can I replace TIP106 by BT151, where gate current (Igt) is only 2mA? The zener & potensio which serially installed, are they affected by current through? By meant We can put any components regardless its staying power?
Thanks.
H Awak, yes BT151 can be used in place of TIP106. According to me the zener and the series resistor/pot are not affected by the current because as soon as the zener conducts the SCR fires and grounds the supply, so the affect of current on these parts are minimal.
Thanks for explanation. Here in my city, quite difficult to get 2uF 400V, if I replace with 1.5uF 400V, what resistor to replace 1M ohm?
Thanks.
Sure, 1.5uF will also do but will provide a maximum of 80 mA current output. The parallel resistor can be still 1 M, it is not critical since it is only used for discharging the capacitor whenever the power supply is unplugged from the mains.
Hi Swagatam;
I am having a 220vac / 9vdc unregulated adaptor 2amp output as printed on its body. I need to test the credibility of the output 2amp.
Would you recommend to shunt 4.5 ohm resistance across its output while measuring the output voltage. If it reads almost 9vdc, then it is a 2amp adaptor?
Hi Rezk, the easier option would be to connect a 10 amp ammeter directly across the adapter output for a couple of seconds, and check the reading on the meter. This would give you a quick and a reliable reading regarding the power supply output current.
Thanks…
Hi Swagatam,
I need a simple regulated & protected transformerless power supply 220VAC/1.5VDC-2 amp, will be used for a gas water heater ignition unit instead of 1.5v battery which depletes fast. I tried several 1.5vdc adaptors available in the market, yet they are either below capacity or does not work long & fails due to high amps needed.
I have seen several circuits, but most are below 2amp output.
Thanks…
H Rezk, transformerless power supply using capacitor at 2 amp current can be dangerous and is not recommended, and also it will be very inefficient at 1.5 V, therefore only SMPS is the recommended option
Thanks Swagatam, I will go for a transformer power supply & add an LM338 regulator.
Welcome for any comments.
You are welcome Rezk, that sounds much better!
Sir,
Can we achieve 12v 2Amp Output with that circuit by increasing capacitors?
or any another solution would you suggest which should be transformer less?
Hello Hafiz, 2 amp can be achieved but the triac may get very hot and waste a lot of energy, that is why an SMPS is always a recommended design instead of capacitive power supplies.
Hi Swagatam,
I use 24V batt for circuit trial up purpose on SCR BT151 circuit above, but the SCR is not triggered using 10K resistor, what suitable value to trigger the SCR? Any formula to calculate SCR gate resistor?
Thanks.
Hi Awak, In that case you can try reducing the 10K to 4k7 and see if that triggers the SCR. I do not have the formula in this website, however, you can refer to the triac concept, and deduce the formula accordingly:
https://www.homemade-circuits.com/triac-circuits-working-and-application/
I have already put in live the circuit & measure output side – without load – that is 245V max & 215V min. I don’t brave yet to put a load where I’m not sure what voltage the actual output is. Base on your design, what is output voltage for this built up circuit?
Thank you.
The output voltage must be equal to the zener diode value. If it is not as per the zener value, then something maybe wrong. Or you can put a 220V load such as a 220V led bulb and check the response
Hi swagatam long time havent mail
Any how your help if possible you can design a battery charger
Your transformerless is ideal
My input 380 to 400vac 3phase and output to 12vdc 12 to 30 amp .
Your is very good in my project which a 3phase 380 to 400 vac output thanks
Hi Sean, thank you very much for your kind words! However, I don’t think 30 amp may be feasible with the above explained circuits.
Happy and Very well thank you.. in your response…….