In this article we study a simple flyback based converter design which is implemented as an SMPS 12V, 5amp battery charger power supply, without using a iron core transformer.
How it Works
The proposed 12V, 5 amp smps battery charger circuit employs a flyback converter topology which results in the required smps based high current, compact, mains isolated converter design.
Here, the a high power mosfet becomes the main switching component and is used for triggering the ferrite primary winding with the set high frequency mains rectified Dc.
When switched ON, the 470k resistor charges the mosfet gate into conduction and initiates the switching action.
The above action induces a voltage across the auxiliary winding of the transformer which results in a feedback voltage to the mosfet gate via the 2n2/100V capacitor forcing the mosfet to conduct even harder.
As soon as this happens, the primary winding gets connected with the full 310V DC rectified voltage via the mosfet drain/source terminals.
During this process, the voltage across the 0.22 ohm resistor situated at the mosfet source tends to cross the 0.6V level, which instantly triggers the transistor BC546, which shorts the gate of the mosfet to ground, rendering it completely switched OFF.
This also ensures cutting-of the auxillary feedback voltage, restoring the entire primary section to its original switched OFF state.
The cycle now begins afresh and is switched continuously at around 60kHz rate which may be varied by increasing or decreasing the values of the 2n2 feed back capacitor and the 100pF base capacitor of BC546 NPN (it's not recommended though).
During the switched OFF periods of the primary winding, an induced equivalent back emf is transferred to the secondary winding which translates it into the specified stepped down low voltage, high current secondary output.
The above secondary output is appropriately rectified and filtered by the high current diode and a filter capacitor.
A feedback stage across the secondary and the primary stages is implemented via a optocoupler which determines the required fixed, regulated output voltage.
The zener associated with the optocoupler may be tweaked for getting different stabilized outputs for the desired applications.
Here it has been fixed to about 14.4V which becomes the optimal level for charging a 12V lead acid battery.
The current output of this transformerless 12V, 5 amp smps battery charger can also be changed by two methods.
Either by modifying the secondary wire thickness of the transformer or by tweaking the value of the 0.22 ohm resistor positioned across the source/ground terminals of the mosfet.
The input stage typically consists of a bridge rectifier stage, followed by an NTC and filter stage.
The input EMI coil is optional.
Recommended for you: 24watt, 12V, 2 amp SMPS using a single IC Must Read.
Circuit Diagram
How to Wind the ferrite transformer
The ferrite transformer is wound over a 15mm EE ferrite core compatible plastic bobbin.
The one half primary is wound first, using a 0.4mm super enamelled copper wire (15 turns).
Secure the end of this on one of the primary side pins of the bobbin. Cover the winding with a layer of insulation tape.
Next wind the secondary winding (5 turns) using 0.6mm wire over it.
Terminate the ends on the secondary pins of the bobbin.
Apply insulation tape over this winding.
On this wind 3 turns of 0.4mm auxiliary winding, cover it with insulation tape.
Finally continue from the secured end of the first primary winding and wind 15 more turns over the above auxiliary wind to finish of the ferrite transformer coils.
Put a few layers of insulation tape to finalize the winding insulation.
Fix the EE cores and tape it yet again along its periphery.
Make sure the EE core edges are separated with an air gap through a piece of insulation tape or a paper, this will prevent core saturation and stalling of the desired smps induction.
THE CIRCUIT EXPLAINED ABOVE IS NOT ISOLATED FROM MAINS, AND THEREFORE IS EXTREMELY DANGEROUS TO TOUCH WHILE EXPERIMENTING IN POWERED CONDITION, AND ALSO THE DESIGN IS RECOMMENDED SPECIFICALLY FOR USERS HAVING ADVANCED KNOWLEDGE IN THE FIELD, NOT FOR THE NEWBIES..
hello sir, sorry for again. sir
1.
I have a faulty cct of a bty belt. it’s ratting are: I/P =220vAC O/P =14vdc, 10 A. can I use this cct’s o/p transformer in this project?
2. If not then if I use this transformer in this project so what can I change/replace in this cct to make compatible with these o/p ratings (14vdc, 10 A). plz need ur guide.
Hello M.Ahsan,
The transformer must be a ferrite core type and the size and the number of turns must be exactly as per the above given specifications, otherwise it cannot be used.
thank you sir.
can I charge 3 series li-ion btys total (11.1v), wd this cct?
3 series cells will require 12.6V, so you may have to adjust the transformer turns to get this output, and also the max current will need to be limited to 50% of the battery Ah rating..
thank u sir , for 12.6 v what are the transformer specifications?
For 12.6V, you can adjust the 13.5V zener diode until the exact 12.6 or 12.4V is achieved.
Hello sir, Can I buy a readymade ferrite transformer with these specifications from market?
Hello M.Ahsan, If you can get the exact specifications then you can buy it readymade.
Can you explain what the function of the 18k resistor and capacitor coupled with it is, and what the effect is if I change the value of the resistor and capacitor?
The capacitor, resistor and the diode together form a high voltage transient suppressor for protecting the MOSFET.
A slight change in the value will have no impact on the overall working of the circuit.
hi swagatam
thank u so much it was good circuit
to build a switching power suply without i.c
best wishes for u
yasin
Thank you Yasin, glad you found the circuit helpful.
Hello sir,
I would like to have your help to design a Charger circuit for LiFePO4 batter of 12V and 5Ah capacity
need to design from the base circuit
Thank you
Hello Pranav, you can try the LAST circuit from the following article. You must replace the battery with your 12V battery, and the relay with a 12V relay, and make sure that charging input is from a constant current source such as from a LM338 current controller:
https://www.homemade-circuits.com/usb-automatic-li-ion-battery-charger/
Thank you sir
Thanks sir
Because 4N35 has 6 pins and circuit shows 4 points of connection so I am not able to connect.
Please compare the datasheet images of the two opto-couplers to confirm and match their pinouts.
Sir can we use optocupler 817 in place of 4N35.
Yes that will also work…
Inductance or air gap
paper gap is recommended between the E core legs…
Sir kindly suggest paper specification to use right paper, I discussed with transformer manufacturer but he requires inductance or paper gap.
You can insert a layer of insulation tape between the E cores.
Hi Sir for 12v 5a SMPS pls suggest the inductance of primary/ secondary coil.
Hi Mayank, sorry inductance details are not available for this circuit, only the winding details are available.
Thank you sir ,15mm EE ferrite core compatible plastic bobbin means
Transformer type and size please let me sir.
Hello K senthil, It is the plastic bobbin which fits between the central limbs of E-core. E core size code is EE15.
Here’s an example:
https://www.homemade-circuits.com/wp-content/uploads/2019/06/ferrite.png
hello sir I want to know that can I use a ATX SMPS transformer core instead of ee15 can it requires more or less turn if increase or decrease of turns please tell me that turns number please reply
I will be thankful for you help and waiting for your reply teacher ????
Hi Biprendu,
The transformer is the crucial part of the circuit, and it should be built exactly as indicated in the article. So I am not sure whether the ATX transformer can be replaced with the EE15 core transformer or not. Since I do not know the inductance values of the transformer, I cannot suggest the adjusted winding details. However, you can experiment with it and see if it works or not. You can connect a 100 watt bulb in series with the input supply while testing, so that your circuit does not burn in case of a malfunction. If the bulbs glows brightly without any load, then your circuit has problems and will need to corrected accordingly.
i have not any ee15 core can you give me some link to buy this transformer or where I can get the ee15 transformer please help me
You can search the phrase “Buy ferrite E Cores” then while ordering specify them about EE15 size. However, the best place to buy them is from any local electronic spare part retailer shop
can you send me ee15 transformer core image and datasheet
You can see the following image:
https://www.homemade-circuits.com/wp-content/uploads/2022/12/15mm-E-core-image-EE15.jpg
i found the transformer from a cfl circuit i match the size and it’s 15mm
That’s great, remember to put a paper gap between the E cores. Meaning when you close the two cores inside the bobbin make sure the E core edges do not touch each other directly, instead put a piece of paper of insulation tape between the edges that meet each other.
ok sir ☺️ thank you for helping me really appreciate to you sir ????
No problem Biprendu, all the best to you.
i found this transformer from cfl and it’s core size was 15 mm
https://drive.google.com/file/d/1pjI0bO1vkRqS2ftb1Izl8xe7TPQO38bT/view?usp=drivesdk
Make the link “sharing” otherwise I cannot access it.
i found this transformer from cfl and it’s core size was 15 mm
https://ibb.co/ctBCPwQ
The transformer in the image should work. Make sure winding fits inside this core properly.
can I use ee13 transformer core please tell me ???? please wire turns for ee13 transformer
EE13 will not accommodate the winding.
Sir, Do you have any SMPS circuit based on DK1203 ?
Hi Sanjay,
Did you refer to the following datasheet, it has all the required details you want:
https://grupoautcomp.com.br/wp-content/uploads/2016/11/Specification-IC-DK1203.pdf
Dear Swagatam,
this datasheet shows ee25 ferrite core, but it is used for a 110v AC input SMPS (Hence Vs =85*1.3=110V) If my input is 220v AC, can I use ee25 ferrite core for assembling this transformer? Is the calculation on this datasheet will be the same for 220v ac input?
Thank ypu for your help
Hi Kamussuwanto,
A ferrite core size should be such that it accommodates the winding comfortably, neither cramming it nor leaving too much free space. So if your EE25 frrite core is not too large leaving too much internal space, then it can be used for the above SMPS.
Dear Swagatam, thank you very much for your quick reply
You are welcome Kamussuwanto!
Sir, Can we modify the above circuit to get output of 80V-10A ?
Which components needs to be added/replaced for the same?
Thank you very much in advance.
Hello Imsa,
For this upgrade you may have to modify the number turns on the transformer. You may also have to reduce the value of the 0R22 resistor at the source of the mosfet. All these will need to be experimented cautiously.
Can you make this 12v 5a smps for me
If I made it, can it use for supply the 22inches led tv ( changhong 22c2600 ) ? Its smps has damaged and the output write on the pcb board is only 12v out for suppying the tv entire system.
Thankyou n I hope you answer me.
If the LED TV is a 12V unit then you can use the SMPS to power it. However I would recommend buying a ready-made unit instead of building one.
I want -14v 0 +14v 5amp ckt diagram and pcb layout
Plz provide me
You can try 12 turns at the secondary of the above design with a center tap and see if that produces the required dual supplies?
Sir please your phone number
hi good teacher. I’d like to ask? what makes 470k and 18k resistors heat up fast? from the first try i have worked perfectly from this schematic but when i made the second one by trying to convert it to higher amperage i have problem 470k and 18k resistor getting hot, other than that everything is perfect only problem is when i make trimpot to get 30v, the resistor starts to smoke, I also change the 10uf capacitor to 100uf, but if I change it the low voltage is 14.4. safe resistor, why is that? I made primary winding 25+25 auxiliary winding 4 secondary winding 5 +5 ct, I combined this schematic with https://www.homemade-circuits.com/how-to-make-variable-current-smps/ to get the correct voltage true can be customized
Hello Zen, It can be difficult to find the exact reason, but you can rectify the fault in the following manner.
Instead of using a single 470K resistor, use two 240K resistors in series. Similarly instead of using a single 18K, try using two 10K resistors in series. Please do not change the 10uF to 100uF, use 10uF only as indicated in the diagram.
okay, thank you my best teacher, for the advice you gave, I have solved this problem by changing the value of the 470k resistor to 680k and 18k to 63k, and the coil that was 5 + 5 secondary, I made it in series without CT, what do you think about the changes do i do that? , now I can turn the trimpot to 35volt safely without heating the resistor, but I haven’t tested it with a load, later if I have tested it with a load, I will tell you my best teacher, greetings and thank you for the guidance
OK, that sounds great. According to me two resistors in series would have worked better, as suggested by me in the previous comment.
okay, I’ll try, the teacher’s advice, from the formula like my previous comment, I have tested it, and the results are not very satisfactory, at a load of 3 amperes, the voltage drops from 35 volts to 13 volts, unlike my first assembly, my assembly the first one, even though the load is up to 5-6 amperes, the stable voltage is still 35 volts, ok sir, I will apply the teacher’s advice by changing the 630k resistor to 470k in series as you suggested, I’ll let you know the results of the load test later
Sure, no problem, you can try it.
Dear Sir,
I like to have a power source of 16V 12V & 5V @ 1Amp to use in circuits such as the 0-100V Adjustable SMPS Circuit in your blog and also in other circuits which can power cooling Fan OpAmps etc. I am unable to built, nor find one.
I tried to make this circuit
copied from your above and Make this 3.3V, 5V, 9V SMPS circuit without actually understanding the working of the circuit! I am at a loss as how to provide feedback to the 5V,12V & 16V Outputs (or will the circuit work?). Could you please advice necessary corrections? Alternately please suggest a suitable circuit.
Thanks in anticipation.
Hi Imsa, In the above circuit, the feedback is already provided to the 16V output using the opto coupler and via VR2. When 16V is controlled, then the 12V and the 5V will be also automatically controlled.
Thanks a lot for your express reply as always !
Does it mean that the circuit given above is expected to work without any changes ?
Thank you very much indeed for your time and advice.
I am glad to help Imsa. If the SMPS is from a reliable source and is a tested design then yes it can be used without any changes.
hi dear teacher. I continued this circuit and I modified the output section using a MUR1560G diode to produce a 17volt voltage with a 25volt 4700uf filter capacitor and a VARIABLE REGULATOR LM317 WITH DARLINGTON MODE AMPLIFIER using tip41 and tip3055. I used 1.5mm 4x copper wire. my question is why does the MUR1560G diode heat up fast? and the regulator heats up quickly even though the load is only 2.5 amperes. that’s the first thing I said. second, when I replaced the LM7812 with a fixed regulator with a 12 volt dc fan load only, the regulator only lasted a moment and immediately broke down and immediately took care of the main mosfet in the primary. Why that can happen, your answer is very valuable to me. greetings from me my best teacher
Hi Zen, as you will understand for any SMPS the transformer is the main element which needs to be wound very accurately, even a slightest bit of discrepancy in the winding can lead to the burning of the devices. By the way did you put a paper gap between the edges of the e-cores which touch other? Make sure you do it otherwise the core will saturate and burn.
At 2.5 amps the MUR1560 can never burn because it is rated to handle 15 amps. I guess the MUR1560 might not be original and therefore it burned at 2.5 amps. I think you should confirm with an ammeter if the output current is really 2.5 amps or more.
So basically you have to add a paper gap between the ecore edges which meet each other.
And also you can add a few more turns on the primary side winding and check if that helps to make the design more stable.
Yes yes..sorry..Master..Accuracy in electronics. It turned out to be very, very important. And the calculated value must be accurate. Sorry sorry teacher sorry for my analysis error. This is not a winding problem or paper defect in the transformer. Everything is correct. But I didn’t really imitate the circuit the teacher presented. I prefer to modify with my knowledge. My problem this time is that I am not careful in choosing components, the MOSFET I bought is IBGT, it turns out that the 20N60 MOSFET has two different letter codes, it could be that the component I bought is wrong. Ah aha.. Now I can solve this problem by replacing the MOSFET with a 9n60 type. And I installed the LM317 variable regulator and its voltage amplifier. And I also included a 7812 fixed regulator for the fan. And everything works fine without overheating at a load of 5-6 amperes and the voltage is stable. I measured all of that with an avometer and a voltmeter. Because at home I have a lot of tools and electronic components. Thank you for your attention, the best teacher. oh..yes someone forgot. I replaced the MUR1560 diode with an HBR2045 diode because the MUR1560 diode has too high an rms for what I need and that could be a problem because I only need 17volt and 32 volts because I wrapped two secondarys inside the transformer
That’s great Zen, I am glad you could solve the problem so effectively. Thanks very very much for your honest feedback. Have a great time with the project.
yes..yes..I am very happy to be able to make the circuit that you present can run well. and this is a very satisfying result for me. even with my heart pounding while testing this circuit. because I have to deal directly with 220 volts AC voltage that can sting me.
This is my first time making a circuit that is directly related to AC voltage, this can replace my iron transformer power supply, for the transformer battery charger I made this is more effective than my iron transformer, this SMPS makes the battery charger full faster than I use iron transformer. However, the weakness of this SMPS is that it does not last long when a short circuit occurs, unlike iron transformers which last a long time when a short circuit occurs, according to my observations. But I am very happy to be able to make it, thank you for the guidance of the best teacher, I will develop this circuit again, because I see SMPS like this, the output section is equipped with many ICs such as the Tl494 IC, there are also those that use LM339N, sometimes the pins are quite a lot. like SD6109, I still don’t understand what the function of the IC in the SMPS output is, its type is like this
Thanks Zen, yes an iron core transformer based power supply will be always more reliable than an SMPS. The main advantage of SMPS is that they are small, compact and lightweight. The above circuit is a very basic design without any ICs…..but the other SMPS designs that you are mentioning are more sophisticated and have more protection stages using voltage regulators and comparators like LM338 etc.
Oh I see.. Yes, does the teacher have a circuit
more protection stage using a voltage regulator and comparator like LM338 On this blog?
Oh yes I observed when I made two secondarys, indeed the voltage would increase if the first secondary installed in the opto was loaded, when I made only one regulator,
Maybe I can work around this by using the same regulator on both secondary. That’s according to my assumption, hehehe… true or not I don’t know yet, I’ll do it soon. But for now I’m only using one regulator, and I’m not using the second secondary, I’ve tested this for a battery charger for about 12 hours with a 0-6 ampere load, the circuit is safe, and it doesn’t overheat, its a bit just a HBR2045 diode that heats up, but I think it’s natural considering the HBR2045 diode is a SCHOTTKY BARRIER diode that has hot properties. Is my observation correct? Good teacher… greetings from me
Actually the protection must be applied through a feedback link which the above circuit has using an opto coupler but using an opamp is also possible. I do not have the design using op amp. If I find one I will surely update it here. Yes you can try using the same regulator for the your two secondaries, hope it works.
I am very happy you could make this simple design so useful, which is now working like battery charger for you. All diodes will usually heat up even if only 50% current flows through them, but I am not sure if a schotky diode can heat up faster or not? I appreciate your efforts!
Thank you very much, for the guidance, the kind teacher. I will also complete this circuit with an auto cut off based on ne555 which is also available on your blog, later I will tell you the results, thank you for your attention answering all my questions about electronics
You are most welcome Zen, all the best to you!
Please I will be glad sir if you can help me out sir I’m 200 level electrical/electronics engineering and I also learn electronics reparing for 5 years before I gain admission in to polytechnic please I’m begging you sir
Thanks for your quick response sir, please can you help me to create +/-14v 80w flyback smps circuit sir to power my tda2030A amplifier, because have try a lot in constructing this many time using Uc3842 but once it gives output and connect it to my amplifier it will on but if I increase the volume to about 45% to 60% it used to kill the power Mosfet and in totally tired of this sir please if you can enlight me on this I will be very grateful sir because i don’t want any other type of smps I want to successful on flyback smps
Azeez, designing a perfect SMPS is a difficult job, and I do not have full expertise in this field so far. I would recommend you to go for a transformer based power supply instead.
Hello Sir, if i want make a 220V to 20V(400W) SMPS, which component should i change?? thanks sir.
Hello Fernandy, you can try modifying the following concept which looks close to your required specifications. You can reduce the secondary number of turns to get 20 V.
https://www.homemade-circuits.com/smps-2-x-50v-350w-circuit-for-audio/
Good evening Sir,
Sir I am having EE25 core, may I use this core . Also I have 20N60CFD , IRF740 . Is it possible to replace IRF740. Sir please guide me.
Hello Swagatam
I really appreciate your work your are really doing a great job kindly keep it up ????
I want to ask you that can I use 0.10mm or any other diameter of wires due to unavailability of wire type used in your circuit ??
If your answer is yes then can you please tell me if I change the wire diameter will I have to change no of turns in primary and auxiliary or not ??
I wants to make 12V 2.5 Amp SMPS Circuit. I tried it using making through 13005 transistors but maximum time transistor burns or didn’t worked properly for me.
Thankyou
Thank you Saurabh,
If thinner wire is used then the E core bobbin should be also selected proportionately smaller, otherwise it may affect the performance, according to me. The rule of thumb is that the winding should accommodate inside the transformer space optimally, there should not be too much space left and also it should not be too much crammed.
If the e core bobbin is correctly selected then the number of turns can remain unchanged.
However I would recommend to follow the schematic details exactly as given, any changes might trigger a fault.