This article will illustrate a simple procedure to devise an unregulated 50V switching SMPS symmetric power supply of 350W. This unit can be substituted with the standard audio amplifier power supply to reduce expense and also the weight. The proposed power supply works as a half-bridge with no regulation.
Written and Submitted by: Dhrubajyoti Biswas
Mosfets as Power Devices
My power supply relies on two N MOSFET and run by IR2153 integrated circuit. The IR2153 is powered by a power resistor of 27K 6W. The ripple at full load is recorded below 2V.
The use of Zener diode (15V) ensures voltage stabilization and the operating frequency is set to 50 kHz (approx.).
At the point of the input, I have placed a thermistor to force a check on the peak current when the capacitor is getting charged.
This same phenomenon can be found in AT/ATX power supply unit of a computer. Moreover, to ensure low leakage inductance and full voltage output, the first half of the primary is wounded in 20 turns followed by the secondary wound.
Also to assure safety in the system, do be sure to connect the output (center tap 0V) to the earth.
Chokes for Filtering RF
The chokes used in the design will facilitate removal of RF output ripple. The number of turns and the core which is found in PC supply is not a critical factor.
Additionally, the 6k8 resistors at the output section is used to discharge capacitors after it is switched off and this way it helps to prevent the voltage increase during no load.
The proposed Switched power supply 2x 50V 350W operates in single switch forward topology. It has an operating frequency of 80-90 kHz and has IRF2153 control circuit which is very much similar to that of US3842. However, the duty cycle is lesser and is limited to 50%.
Rewinding an ATX Trafo
The Tr1 transformer was devised by rewinding the SMPS ATX transformer and its primary inductance is 6.4 mH (approx.).
The core of the system has no air gap and the primary inductance is further broken in two parts: The first half is the wind and the second is the winding.
Moreover, it is also feasible to deploy the original primary bottom half without rewinding. This type of power supply aptly suits for power amplifier applications.
If required it may be also safeguarded against overload or short circuit and the voltage of the output could be stabilized. The Feedback of the system may be enabled through the help of optocoupler.
It is important to note that in regard to 350W power, care should be taken that in the conductive state the typical resistance should not cross more than 0.8R. MOSFET can also be used to lower the point of resistance.
Interestingly, the smaller the resistance better is with the system.
The voltage tolerance is in the range of 900-1000V. In the worst case scenario 800V can be used. Considering this, the best MOSFET I found was SPP17N80C3 or 900V IGBTs.
Circuit Diagram
Coil Winding Details:
- The main SMPS transformer which can be seen integrated with the MOSFETs may be wound on a standard 90 by 140 square mm ferrite bobbin core assembly.
- The primary side winding consists of 40 turns of 0.6mm super enameled copper wire.
- Remember to stop after 20 turns, put an insulation layer with an insulation tape and wind the secondary winding, once the secondary is wound, insulate it again and continue with the remaining 20 turns over it.
- Meaning the secondary winding gets sandwiched between the primary 20 + 20 turns.
- The center tap of this 20+20 may be connected with the body of the SMPS for an improved stabilization and cleaner outputs in terms of ripples or buzzing interference.
- The secondary consists of a center tapped 14 x 2nos turns made by winding 0.6mm super enameled copper wire.
- The input and output filter coils may be wound on ferrite torroidal cores. The paired winding must be wound on the same individual torroidal cores using 0.6mm super enameled copper wire with 25 turns on each arm of the relevant supply terminals.
Update:
The above design 350 watt SMPS circuit was further improved by one of the dedicated members of this website Mr. Ike Mhlanga. The complete schematic of the same can be witnessed in the following figure:
Questions & Answers
Hi,
Can anyone explain how the second circuit by Mr. Ike Mhlanga does voltage regulation. The optocoupler is put across +50 and -50 output, so it regulates both the rails together, not each rail. In audio, there is load on one rail only at any given time so this regulation is not ideal, am I missing something?
Hi, the opto is only detecting the over voltage situation and regulating the secondary side overvoltage situation.
When a load is operating at the output, the overall voltage will drop, so the opto will remain inactive most of the time…so it has nothing to do with dual nature of the output DC…
Swagatam,
The Transformer calculator is relatively easy to understand than the wire current calculator. To deliver 850Watts@55 volts, the current max capacity should be 15.45A per rail (+ve & -ve). I am thinking of putting two separate SMPS per channel that is expected to deliver 100W into 8 ohms, 200W into 4 ohms and 400W into 2 Ohms. Adding 26W idle power consumption
to it I need the SMPS of 450W per channel. I am aware that the entire value chain should comply with the increased power capacity – right from input mains rectifiers to output rectifiers with the transformer and the IGBTs/MOSFETs in between. What type of ferrite core (dimensions) would you suggest with the Np/Ns ratio with the wire diameters for primary and secondary. Apologies for bothering you.
Hi Prasanna,
The wire current calculator page has another calculator at the bottom section of the page, which directly calculates the approximate thickness of the wire, depending on the current spec flowing through it. However, estimating the bobbin size and E-core could be a matter of experimentation through some trial and error.
Alternatively, as explained in the SMPS calculator page, you can customize the E core/bobbin size simply by adjusting the frequency value such that the number of turns just fit inside the desired E core/bobbin setup. Because, as we know, as the frequency is increased, the number of turn decrease and vice versa. Let me know if you have any further doubts.
Agree. Increase the frequency or the number of turns to get higher voltage. But we have to make apt choice between the two to keep losses and hence the ambient temperature minimal.
My amp mandates peak current of 21.2A/rail for 1V rms input when driven with 2 Ohm load (worst case scenario). When put in the wire diameter calculator on the page suggested by you it gives me 3mm wire diameter. (I assume it’s for secondary). To accommodate such a thick wire, I should go for ETD22 ferrite bobbin which is proposed on some other site for 400W. I really need to obtain the core and give a try.
Yes, you are correct regarding the losses and noise.
It can be for the secondary or primary, it solely depends on which side current (I) is being measured. But yes, since 21 amps looks too big, and cannot be on the 220V side, so it has to be on the secondary side.
You can use Litz wire which can further help to keep the transformer dimensions compact and yet fulfil the high current requirements efficiently.
Thanks Swagatam, I will give a try and revert.
No problem Prasanna, all the best to you!
Swagatam, I need 55V Symmetrical output with max 850W output. I have a couple of questions 1) What should be the dimensions of the Ferrite bobbin. Should it be square only or the ring will also work. 2) What should be the diameters of the coper wires for primary and secondary windings.
Hi Prasanna, You can go through the following articles to get an idea of all the basic parameters required for designing a customized SMPS circuit. For the output voltage you can select 55 + 55 = 110V. Let me know if you have any further doubts or questions.
https://www.homemade-circuits.com/56492-2/
https://www.homemade-circuits.com/smps-transformer-calculator-2/
Thanks Swagatam.
sorry the above comment was a mistake, feedback already provided in the subsequent circuit. thanks.
No problem Imsayuba…glad you found the design you wanted.
Sir, can we add a Feedback circuit for voltage regulation? if yes, could you please show in the schematic?
good 👍
Hi Swagatam can a similar power supply be designed using TL494 as I have a few if these ICs ..
Hi Andrew, I am not sure how a TL494 can be configured like a half bridge inverter using a bootsrapping network, so i think it may not be easy to replicate the same above design using the TL494.
Hello Sir,
I need 2x45v,15 Ampere power supply for audio amplifier.
Also is it possible to rewind a transformer in place of an SMPS bobbin with keeping in mind primary for 25 volt.
Hello Ajay,
I would suggest you to first build and try the above circuit, if you succeed then we can adjust the transformer specifications to suit your requirements.
Sorry i did not understand your second question? Do you mean using an iron core transformer in the above circuit, no that’s not possible.
Thank you so much, Sir. Can you please provide the specifications of the SMPS bobbin?
Or can I rewind it on the computer supply SMPS?
You can use any ferrite bobbin which accommodates the complete winding, as specified in the article.
However, as per the article, 90 by 140 square mm ferrite bobbin is the exact specifications of the bobbin
Hello. I intent to make this SMPS Power Supply. I am doing it for the first time.
How I see there is work with high voltage and it should be dangerous for a beginner.
Is it possible to use this kind of filter as change for the first part of this circuit diagram?
It should be better for me to buy finished ones?
FILTER Type 2470
mgelectronic.rs/filter-za-rso-tip-2470
FILTER Type YB10T1
mgelectronic.rs/filter-za-rso-tip-fyb10t1
yunpen.com.tw/en/product/IEC-Inlet-Filters_YB-T1.html
Hi, yes those filters can be used at the input side of any SMPS circuit.
Thank you.
90by 140 Sq mm BOBBIN means. I don’t understand
It is the dimensions of the ferrite core bobbin, 90 sq mm is the vertical side height x width dimension, and 140 mm is the length and breadth of the top side dimension.
Hello swagatam first of all thank you for this circuit I was looking for something like that suit my project and i have founded on your website I have maded this circuit and got 48.3v at the output but when i connected some load there’s no voltage at all however I think that for the constant voltage i should have to connect an output coupler and after that i should connect the load !
Thank you Salman, The above circuit was not designed by me, and I do not have sufficient information regarding this circuit, therefore it can be difficult for me to help you with this design.
optocoupler is important for the feedback without it SMPS will do switching first and after that it will not switch optocoupler will give the SMPS feedback and after that it will do switching continuously and it will make real voltage am i right sir ? Do you know how to integrate optocoupler in this circuit?
Optocoupler feedback is important only for regulating the output voltage to a fixed level. It has nothing to do with the generation of the output voltage. Even without the optocoupler the output should be able to handle a connected load.
Yes it means your problem is not solved yet.
360mV is too low, that could be a leakage voltage also, it does not indicate your IGBTs are switching the transformer.
Please confirm it with the diagram, if it matches the circuit diagram then it is correct.
Thanks alot. The circuit works very well . But sensitive to short circuit. It would be good if it’s modified to have short circuit protection
Thank you Aluda, Glad you could build it successfully. Yes the circuit is not protected from an output short circuit, which must be corrected.
Hi engineer. How can I get additional 12 0 12 from this circuit ?
For powering preamplifier
Hi Aluda, you can use a 7812 and 7912 IC circuit for getting the +12V and -12v outputs from the 50 V outputs.
Okay thank you
Any PCB for the circuit?
Sorry, PCB is not available for this project.
Kindly share PCB for this circuit. I will appreciate
The first, top diagram.
Please read the point number 7 under “Coil winding details”.
You can use a bridge rectifier but it should be rated to handle at least 3 amp current and have a PIV of 1000 V, just like the diodes 1N5408.
MOSFETs are SPP17N80C3, the diode numbers are given in the diagram, the NTC is 5D-11
Hello sir you were right the beginner can’t to the professionals work.
But still i have a question this circuit diagram can be also used for 24v 10a SMPS
?
Is that Voltage and amps are depends on the winding of the transformer ?
Hello John,
The above circuit can be used to produce 24 V 10 amp by suitably adjusting the secondary winding.
Voltage and current depends on the transformer winding, and the MOSFET rating.
And can we up and down the voltage in this circuit?
No, that’s not possible.
If your 220 V AC is fixed then the SMPS output will be also fixed…
And nothing will change instead of windings and mosfets ? Everything will be same ?
That is correct.
Sir can you give me clear image i can’t see components name both pictures aren’t clear enough!
John, the image is quite clear, I can see all the numbers correctly, please let me know which part number you are not able to understand.
So sir it’s a 24v 15a SMPS design??
Yes it should produce 15 amp current, if the output winding is adjusted to 24V output.
As warned before if you are a newcomer and have no experience with SMPS circuits, you will probably fail to build this design successfully and in fact you might end up up burning something or meet a fatal accident.
I need 2x50v,350w power supply for audio amplifier.how I get this p/s
You can build the above explained circuit….
Thank you sir for ur assistance.I appreciate.
Thank you sir for responding so quickly.on the link you reffered me, what modification can b done to it for dual rail voltage?
For converting into dual voltage you will have to create a center tap across the secondary winding, and then add the rectifier, filter stages as done for the circuit in the above article.
Hi sir pls I wish to build a dual rail power supply just like this one to power an amplifier. Is it possible to build it with 3844 ic.if yes pls can u suggest me a circuit diagram?
I’ve seen in some home theater system
and DVD player that have just one MOSFET switching the primary winding of the transformer and the secondary side has dual supply to power operational amplifiers n I don’t know the kind of topology used.though I’m a learner.so I keep wondering if could build such kinda power supply but I really need guadiance on this.
I tried building this circuit but blew couple of those transistors which are quite expensive where I am.please sir I need ur assistance.
Hi Abubakar,
The above design is a tetsde one and it worked fine for many readers, I am not sure why you could not succeed with it.
You can try searching “Switched power supply 2x 35V 350W using IC 3844” you should be able to find the required design using 3844 IC.
I think I have a single mosfet based SMPS in this blog. You can refer to the following design:
https://www.homemade-circuits.com/12v-5-amp-transformerless-battery/
hi sir..i know you are profesional..i have aquestion::i want a powersuply like you desined but i need(+170volt and -170volt..with 1amper )))in out put what sould i do??please lead me and thanks
Hi Muhammad,
You can try increasing the number turns at the secondary side until you get the 170V output. This is my assumption I am not fully sure about this. But you can try this.
Do you have design of regulated Switch Mode Power Supply of 50V 300W or 50V less watt , but it needs to be regulated to 50V under varying maximum load condition 5A?
The regulated version of the first circuit is shown at the end of the article.
Is it a closed loop microcontroller based power supply?
Does the output voltage 50V remain constant under varying load condition of 0-7A?
Does the output voltage 50V ,changes with changing load current?
It is an SMPS based power supply but it does not have a feedback control, so the output voltage will not be constant 50 V.
But you easily add a opto coupler based feedback loop mto keep the output constant.
The transistor collector of the opto can e configured with pin#3 of the IC IR2153 for the required automatic voltage correction.
Actually this configuration is shown in the last diagram
Can we use transformer core on which number of windings of copper wire are made to form chopper?
Is the chopper used in switch mode power supplies same as the transformer core on which copper winding is done?
How do we determine, how many turns are to be made on primary side and on secondary side for design of 350W power supply?
Sorry, I could not understand your first question regarding chopper winding?
For the number of turns on an SMPS transformer you can use the following article for the calculations:
How to Calculate Ferrite Core Transformers
Do you have Proteus digram for this circuit?
Sorry, I do not have a Proteus diagram for this project
Need help in designing closed loop buck converter of 20A 50V
What turns of Switch Mode Power Supply transformer primary and secondary you keep.What diameter of copper wire you used?
Will our circuit run if we plug in the single phase from the bridge rectifier and no using input filters?
The turns will be the same as explained in the above article, but the thickness of the wire will need to be experimented. I think for a 20 amp transformer, the primary side will need to be built with 1.5 mm thick wires, and the secondary side with 2.5 mm thick wires. The circuit can be used without the filter also.
Hello sir!
if I want to increase the output, for example I want to increase the output of 12, 9 and 5 volts. do i just add a regulator ic to the output?
thanks sir
Hello Fernandy, you can add voltage regulators but they can too hot when a load is added, instead you can measure and extracts taps from the secondary winding appropriately corresponding to the 12, 9 and 5V.
Hi Swagatam, i built your amp design awhile ago and was very successful !!. I’m trying repair/modify a SMPS for an expensive power supply(to replace) ,it seems to be flyback design , i built a circuit based on IR2153 very similar to above design from application notes for IR2153, i’m only getting a pulse on pin 5 to drive mosfet, when i connected circuit to drive primary winding on SMPS the fet on pin 5 exploded, i isolated the transformer from driver circuit of damaged PSU completely, how can i make/modify this design to drive an unknown primary winding, by adjusting frequency until correct saturation is reached , should frequency be adjusted from low value to high value or vise versa, or …………..
Hello Mr Andrew and Mr Swagatham as well. Although your post is quite old and scince your application was a little unusual, I wish to point out something interesting that we service technicians come across from time to time. This is about a Chinese SNPS module that is reasonably powerful, quite reliable, easy to fit n forget as well. This is commonly available at many el spare parts dealers and not to expensive as well and its a straight replacement for the drive/opt stage of Crt Tv,s and more, across almost any voltage and current ranges. These unit comes in 4,5,6 wire versions so select the appropriate one for your req. This versatile unit can be felt used to drive Tv,s,Cd players, battery chargers etc. in short you have to only “mate” it intelligently with any unknown pwr unit disconnecting the C of the previous Opt and connecting the +Ve as mentioned in their leaflet and turn it on. This is of course based on the assumption that the circuit “After” the SMPS Transformer is Ok(No short ckt etc) Hope this works for you. Have a nice day.
Thank you Prashanth!
Hi Andrew, SMPS are usually built with a lot of calculations, however you can try this quick remedy.
You can put a 40 watt AC bulb in series with the input AC, and then gradually adjust the frequency until you find the lamp shutting off completely.
Then with this set up you can add a load at the output of the SMPS and check if that proportionately causes the glow on the lamp to increase.
In this way the right matching frequency could be perhaps confirmed.
I have found this quite an interesting article, will have a little experiment!
One value I am not sure about (on the updated version from Mr Mhlanga) is for the Trim Potentionmeter R8? I am assuming it needs to be fairly large say 20K to keep it off and trim to just the right level at full current but I could have this wrong?
I am assuming that the 2.2uf capacitor needs to be 400V? albeit If I am thinking correctly this and the two 1000uf capacitors run at half rail so maybe 200 ish would be fine? I plan on using 400v throughout but for cost reasons this may be a reasonable approach.
(The 470uf Capacitor seems to be marked as 50v, that is probably better at 63v to give a bit of margin).
once again thanks not just for the article but your patient responses to all the posts.
Glad you liked the article, hope it works for you!
The R8 is actually wrongly placed. It should be placed in a resistive divider manner with reference to ground. In the indicated position it will do nothing except limiting the LED current, which is already limited by R7.
Yes the 2.2uF can be a 400V capacitor.
I would recommend using 400V for all the AC related capacitors, for ensuring extreme safety.
Yes the output 470uF capacitors must be rated at 63V or 100V for better safety.
Great thanks for the feedback, I am not sure this part of the circuit will work as defined even with that tweak, could just be myself not understanding the circuit, the rest looks fine. So I will experiment with the sense circuit before commiting to a board!
I will probably evaluate using a zener like in one of your other designs as that is something I am more used to using.
Sure, no problem, you can also experiment with TL431 instead of the zener diode
Dear Swagatam I am looking for a Schematic for 45-0-45 volts (2Amps) 0-12 volts 1amp and 5volts 1amp to drive a preamp if you could help me Thx. Peter
Swagatam Thx for that, Peter
Hi Peter, I don’t seem to have a transformer based 45-0-45 V power supply design. The SMPS version is shown in the above article. The 12V and 5 V could be probably derived by adding additional windings on the secondary side of the transformer.