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PWM Inverter Using IC TL494 Circuit

PWM Inverter Using IC TL494 Circuit

A very simple yet highly sophisticated modified sine wave inverter circuit is presented in the following post. The use of the PWM IC TL494 not only makes the design extremely economical with its parts count but also highly efficient and accurate.

Using TL494 for the Design

The IC TL494 is a specialized PWM IC and is designed ideally to suit all types of circuits which require precise PWM based outputs.

The chip has all the required features in-built for generating accurate PWMs which become customizable as per the users application specs.



Here we discuss a versatile PWM based modified sine wave inverter circuit which incorporates the IC TL494 for the required advanced PWM processing.

Referring to the figure above, the various pinout functions of the IC for implementing the PWM inverter operations may be understood with the following points:

Pinout Function of the IC TL494

Pin#10 and pin#9 are the two outputs of the IC which are arranged to work in tandem or in a totem pole configuration, meaning both the pinouts will never become positive together rather will oscillate alternately from positive to zero voltage, that is when pin#10 is positive, pin#9 will read zero volts and vice versa.

The IC is enabled to produce the above totem pole output by linking pin#13 with pin#14 which is the reference voltage output pin of the IC set at +5V.

Thus as long as pin#13 is rigged with this +5V reference it allows the IC to produce alternately switching outputs, however if pin#13 is grounded the outputs of the IC is forced to switch in a parallel mode (single ended mode), meaning both the outputs pin10/9 will begin switching together and not alternately.

Pin12 of the IC is the supply pin of the IC which can be seen connected to the battery via a dropping 10 ohm resistors which filters out any possible spike or a switch ON surge for the IC.

Pin#7 is the main ground of the IC while pin#4 and pin#16 are grounded for some specified purposes.

Pin#4 is the DTC or the dead time control pinout of the IC which determines the dead time or the gap between the switch ON periods of the two outputs of the IC.

By default it must be connected to ground so that the IC generates a minimum period for the "dead time", however for achieving higher dead time periods, this pinout can be supplied with an external varying voltage from 0 to 3.3V which allows a linearly controllable dead time from 0 to 100%.

Pin#5 and pin#6 are the frequency pinouts of the IC which must be connected with an external Rt, Ct (resistor, capacitor) network for setting up the required frequency across the output pinouts of the IC.

Either of the two can be altered for adjusting the required frequency, in the proposed PWM modified inverter circuit we employ a variable resistor for enabling the same. It may be adjusted for achieving a 50Hz or 60Hz frequency on pins9/10 of the IC as per the requirements, by the user.

The IC TL 494 features a twin opamp network internally set as error amplifiers, which are positioned to correct and dimension the output switching duty cycles or the PWMs as per the application specs, such that the output produces accurate PWMs and ensures a perfect RMS customization for the output stage.

Error Amplifier Function

The inputs of the error amplifiers are configured across pin15 and pin16 for one of the error amps and pin1 and pin2 for the second error amplifier.

Normally only one error amplifier is used for the featured automatic PWM setting, and the other error amp is kept dormant.

As can be seen in the diagram, the error amp with the inputs at pin15 and pin16 is rendered inactive by grounding the non-inverting pin16 and by connecting the inverting pin15 to +5V with pin14.

So internally the error amp associated with the above pins remain inactive.

However, the error amp having the pin1 and pin2 as the inputs are effectively used here for the PWM correction implementation.

The figure shows that pin1 which is the non-inverting input of the error amp is connected to the 5V reference pin#14, via an adjustable potential divider using a pot.

The inverting input is connected with pin3 (feedback pin) of the IC which is actually the output of the error amps, and enables a feedback loop to form for pin1 of the IC.

The above pin1/2/3 configuration allows the output PWMs to be set accurately by adjusting the pin#1 pot.

This concludes the main pinout implementation n guide for the discussed modified sine wave inverter using the IC TL494.

Output Power Stage of the Inverter

Now for the output power stage we can visualize a couple of mosfets being used, driven by a buffer BJT push pull stage.

The BJT stage ensures ideal switching platform for the mosfets by providing the mosfets with minimum stray inductance issues and quick discharge of the internal capacitance of the fets. The series gate resistors prevent any transients trying to make its way into the fet thus ensuring the operations to be entirely safe and efficient.

The mosfet drains are connected with a power transformer which could be an ordinary iron cored transformer having a primary configuration of 9-0-9V if the inverter battery is rated at 12V, and the secondary could be 220V or 120V as per the user's country specs.

The power of the inverter is basically determined by the transformer wattage and the battery AH capacity, one can alter these parameters as per individual choice.

Using Ferrite Transformer

For making a compact PWM sine wave inverter, the iron core transformer can be replaced with a ferrite core transformer. The winding details for the same  may be seen below:

By using super enamelled copper wire:

Primary: Wind 5 x 5 turns center tap, using 4 mm (two 2 mm strands wound in parallel)

Secondary: Wind 200 to 300 turns of 0.5 mm

Core: any suitable EE core which would be capable of accommodating these winding comfortably.

TL494 Full Bridge Inverter Circuit

The following design can be used for making full bridge or H-bridge inverter circuit with IC TL 494.

 

As can be seen, a combination of p channel and n channel mosfets are used for creating the full bridge network, which makes things rather simple and avoids the complex bootstrap capacitor network, which normally become necessary for full bridge inverters having only n channel mosfet.

However incorporating p channel mosfets on the high side and n channel at the low side makes the design prone to shoot-through issue.

To avoid shoot-through a sufficient dead time must be ensured with the IC TL 494, and thus prevent any possibility of this situation.

The IC 4093 gates are use for guaranteeing perfect isolation of the two sides of the full bridge conduction, and correct switching of the transformer primary.

Simulation Results

SHARING IS CARING!

About the Author

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



151 thoughts on “PWM Inverter Using IC TL494 Circuit”

  2. Hi
    I built your circuit and connected it to a 40 Watt 0-7.5-0 transformer and I have 3 issues with this circuit now :

    issue1) When I connect my laptop adapter, the output frequency is distort, and a hammering sound starts from Transformer. The re is no effect if I try to compensate with frequency Pot; only the tone of the sound changes.

    issue2) The output voltage is changed if I connect different loads, and for every load, ex. lamp or charger, one should proceed to correcting with PWM Pot every time.

    issue3) When I try to parallel Mosfet output stages with the same Mosfet configuration, the no- load current increases and Mosfets get hot, and I cannot increase the wattage of the circuit. How can I increase wattage?

    Thank You.

    • Hi, please check the frequency that you are getting from the output of the transformer, it must not be high.

      secondly I could not understand your transformer rating? what does 0-7.5-0 mean? I could not get it.

      The transformer rating, the frequency and the load current must all be compatible with each for the proper functioning of any inverter, make sure these are all correctly selected.

      • I meant this type of a metal-core transformer : 7.5-0-7.5 in primary and 220 at secondary . Sorry that I made mistake when writing its specifications last time.
        Also, in frequency section of the circuit, The only difference with your posted circuit is that I put 33k resistor between pin 6 of TL494 and ground instead of potentiometer and 4.7k in your posted circuit; all other capacitors and resistors are same as your posted circuit.

        The laptop AC adapter is ASUS model : ADP-65GD B : input AC100-240V 50-60Hz 1.5 A & output : +19v DC 3.42A.

        I do not have frequency meter, but clearly there is a sound difference when I connect this ASUS laptop computer adapter . and I repeat for you my 3 issues here:

        issue1) When I connect my laptop adapter, the output frequency is distort, and a hammering sound starts from Transformer. The re is no effect if I try to compensate with frequency Pot; only the tone of the sound changes.

        issue2) The output voltage is changed if I connect different loads, and for every load, ex. lamp or charger, one should proceed to correcting with PWM Pot every time.

        issue3) When I try to parallel Mosfet output stages with the same Mosfet configuration, the no- load current increases and Mosfets get hot, and I cannot increase the wattage of the circuit. How can I increase wattage?

        • What is your transformers current rating and battery Ah rating?
          You must check the results with a 100 watt bulb first, makes sure it illuminates smoothly.

          Frequency is very important, you will have to check and make sure it is within 50Hz if the transformer is an iron, however a TL494 may not allow you to reduce the frequency below 1kHz…as per the datasheet.

          power can be increased by increasing the transformer, battery and mosfet rating together.

          • I checked with 3 lamps totally around 100 watts and I gained exact 220V AC across them with no drop -down of voltage while my voltmeter shows 336 VAC at no-load.
            The AH of the battery is 65AH ; a new typical car battery, no problem with that.
            The transformer is a 40Watt 7.5-0-7.5 to 220 with a iron core size of 6.5cm-3.5sm.
            Is it good to make an increase in number of Mosfets with a 100 ohm resistor connected to EACH gate of a single 100 ohm resistor for all mosfets is enough? can you put the suitable circuit showing how to increase the number of mosfets?
            or any suitable LC filter at the output to stop the hammering sound when I connect this Laptop adapter to the output?
            Thank you.

            • Power handling capacity can be increased by putting mosfets in parallel but here it won’t be useful, because your transformer is 40 watt, single mosfets would be enough to handle that much power.
              You can think about increasing mosfets numbers only if your transformer is rated at 300 watts or 500 watts.

              I think instead of TL494 you should try some other inverter circuit such as using 4047 or using transistors.

              and if possible use a 12-0-12V transformer if the PWM function is not being used, that will give you around 220V output, the hammering sound could be due to high voltage from the transformer.

  6. Hie Sir.

    Can you please help me with a complete schematic of the driver stage intergrated with bootstrap for high side switching that will drive h-bridge instead of this half bridge. I intend to use it with tl494 modulations ,the h bridge will be connected to 380vdc.

  7. greetings
    I want to wind a transformer using the core area and ferrite core with 12vx2 input and 11v output with the frequency of 1.2khz.
    can you please show me how did you compute for the sizes of magnet wire and the number of turns

    • sorry, I have no idea regarding the calculations of the inductor…this design was taken from the datasheet of the IC ready made. You can perhaps give it a try through some trial and error…

  10. Hi sir, you mentioned an how to use ferrite core, pertaining number of turn but you didn’t say about switching frequency, will it work the same with 50 or 60Hz?

  13. hi swagatam,

    it is possible to add such a protection circuit to detect if any short circuit on the secondary (220V) side , possibly add a relay to protect the mosfet ?

    I am going to build these with 8pairs of mosfet IRFZ44N to drive the iron cored trafo.

    Any advice really appreciate

    thank you

  17. The transformer that you have mentioned is having 400 turns ratio.Considering 230v at secondary,primary will be less than a Volt. Am I making a mistake ? Pls guide.

  18. You have mentioned in the design that for compact design iron core can be replaced with ferrite core.My question is ferrite core is used with high frequency & iron core is used for lower frequency. How without making any changes in the design iron core can be replaced with ferrite core ?

    • obviously you will have to use high frequency for a ferrite trafo, that's an understood fact, I might have not mentioned it because it's not the main subject of the article, I have only given a optional suggestion.

  20. Dear Kaustav, I got the diagram from another site, it's not my design

    The "recommended" minimum oscillator frequency (not PWM) is 1kHz, but you can try reducing it upto 100Hz….if it doesn't work normally then you could probably try a SG3525 based designs which has exactly the same features without restrictions.

  21. hai boss
    when i adjust pwm pot suddnly out put gone and one mosfet burnt
    also i try three times to add two fets but failled.
    now i m going to add two fets again by connecting two gates together and gives one gate signel both
    using one resister
    .what will happen

  22. Hello,

    Really helpful post. Can I use this circuit for high frequency inverter (110V, 800 HZ). Should I use a high frequency transformer for it. Please suggest required changes if any.

    Thank you.

    • yes you can use it for the mentioned frequency, for 800Hz a laminated iron core will work, no need for a ferrite core transformer.

      except the frequency all can be exactly as shown

  23. hello
    we cannot add more mofets in parallea to this mosfet driver part.all bjt get burnt and fets also burnt
    .so this cannot upgrade for higher wattages.
    i connect two mosfets to driver cct using two 4.7 resisters.
    but all bjt burnt /mosfets burnt /ic burnt

    • No that's incorrect!!
      the BJT stage cannot get loaded or affected due to a mosfet because mosfet gates have a very high resistance, and on the other hand the BJTs cannot impact the gates of the mosfets again because of the high resistance of the mosfet gates

      your mosfet could be getting damaged due to some other reason.

      and mosfets in parallel can definitely be added with the shown BC547/BC557 stages.

    • It is not absolutely necessary to add resistor across gate and source but you can try it if you wish…the mosfet must be positioned as close as possible to the BJT buffer stage.

      yes diodes could be crucial and is recommended across the source and drain of the fets.

  27. thank you for reply. i made this cct and it works well two times .but after i put another mosfet in parell.then all transisters damage .after remove mosfet the cct not working now.
    i replace transisters and ic .but now pin 9 output only occilating .pin 10 line not working.
    how to correct this.

  28. Hi Swagatam,
    I am doing a project where I need to generate a pwm signal for a 35 V DC input using TL494. The output should be a wpm signal of same voltage. Can you please tell me how to use it to get a pwm signal? I have been stuck on this problem for quite some time now.

  29. Hi Swagatam,
    I am doing a project where I need to generate a pwm signal for a 35 V DC input using TL494. The output should be a wpm signal of same voltage. Can you please tell me how to use it to get a pwm signal? I know the question is completely off the topic but I have been stuck on this problem for quite some time now.

  32. Ur circuit schematic working well on my bread board – thanks . I used a old 15v-0V-15V transformer removed from a old dead UPS thus i got 150V – 160V from a 12V, 2A battery. Tried and failed to shut TL494 down like her close relatives – SG3524/3525.. Perhaps i concentrated my experiment on Pin 4….. I got one IC damaged already… Please do u have any idea or suggestion how i could shut TL494 oscillation down??….Please u can reply me here or via sammytrench@yahoo.com

  33. Hello Mr.Swagatam,ahmad from Indonesia I'm sorry if my english is very ugly I hope you can understand my situation, I have some questions:
    1. whether the value of the capacitor on pin 5 it can be replaced, because I had trouble getting capacitor with a value 220nf
    2. whether veriabel resistor on pin 6 (100k) and pin 1 (10k) it needs to be played back or regulated, how.
    Thank you very much

    • Hello Ningrat,

      you can try some other closer value for 220nF or use two 100nF (0.1uF) in parallel

      I have explained the control and calibration procedure in the article, please go through it carefully

    • Hi, sorry you cannot use the above circuit without a center tap trafo, it may be possible but could make the circuit much complex
      instead you can try full bridge driver IC for operating a transformer without a center tap.

  36. i made this inverter exactly the way you designed it and it worked. I used it to power 100w bulb. I used a ferrite transformer i found in my damaged Chinese 12v 1000w compact inverter, though it was labelled 1000w but I doubt. Now, I want you to help me increase it to 36v 2000w. I know that the IC will be fed with 12v, I will use 7812 and 7824 regulators ic to regulate 36v to 12v for the circuit. What will be the turns of the ferrite transformer for 2000w? if i want to use a high frequency, i know that i have to select rt/ct network to obtain the high frequency. i want to know the frequency suitable for a 36v 2000w compact inverter using a ferrite transformer? Thanks

  37. Hi,
    Great web site and you must be very busy with all these circuits.
    I have what maybe a dumb question, when you say "primary configuration of
    9-0-9V" for the sine wave PWM inverter, do you mean 9 turns to center tap?
    I see you have 9V there, does that mean 9Volts? Or a transformer which would
    be 9V if you were to connect 220vac to the secondary as if it were the primary
    in a step down application?
    Thanks!
    Marc

    • Hi, thanks

      It means that the primary should be rated at 9V-0-9V with reference to the 220V secondary.

      yes that's right if 220V was supplied at the 220V side that's supposed to generate a 9V-0-9V across the other side.

  39. Hi Swagatam,

    I'm testing this circuit on breadboard. I'm using the same values as you have mentioned. I'm using a 12-0-12 10A transformer. When I check the output voltage, it's in the range of 300v. Adjusting PWM control has no effect in the output voltage. The output frequency is about 35KHz (checked after stepping down). When I adjust the frequency pot, it reduces a little. but not much. Shouldn't the frequency read in the range of 40 – 80Hz? Why it reads 35KHz?

    When I look at the datasheet, I see that this is the formula for Frequency.

    Single-ended applications:

    f = 1/Rt*Ct

    Push-Pull applications

    f = 1/2Rt*Ct

    I believe this is a push pull application and if we use the second formula with the values you have given:

    1/2*15000*.000000001 = 33333Hz.

    This is the frequency I measure after stepping down the output.

    But if I make these changes according to the formula:

    F = 1/2*45000*.00000022 ~ 50Hz. (100K VR set to ~45K and a 220nf). With these changes, I get correct 50Hz. Now my multimeter measures 250v but I'm still not able to adjust the voltage using the PWM pot. Should I add a feedback from the output?

    please let me know if what I'm doing is correct.

    Thanks,
    Vijay

    • Hi Vijay,

      the PWM pot is referenced to ground, please check whether you have connected the ground with the PWM pot or not, otherwise it will not work.

      after connecting make sure the pin#1 voltage changes when this preset is adjusted….this is supposed to change the reference voltage for the error amp which in turn is supposed to narrow or widen the PWMs

      or simply short the pin#1 with ground and see the response.

      I'll the frequency components values in the diagram soon.

  40. very impressive circuit, its working on high freq. 16khz and low freq. 60hz. the only problem here is the pwm control, yes we can adjust the voltages in fix value. but when the source voltage up let say 12v to 15v the output voltages also increases. unlike my current pwm squarewave sg3524 has a perfect voltage control even we use 12v-24v supply the output voltage remain steady. sorry for my bad english, i will appreciate if our master fix or correct the pwm section thank you. God Bless!

    • OK thank you very much, in that case I'll request you to check the two designs and find out the what may be causing the two designs to work in slightly different ways, because I have configured he pinouts as per the datasheet of the IC and exactly as per the pinout functions of the IC.

      By the way the above circuit does not include an output voltage correction circuit stage…that's an external ad-on circuit which may be required for controlling the output voltage, and may be that is why the above circuit is not controlling the output voltage.

    • my bad i though this design got output voltage controller. sorry for my comment earlier, pls help us to attach the voltage controller on pin 1. theres another question i would like you to know, why when we use the push pull transistor the transformer generate to much noise, yeah the gate voltage become high if we use push pull transistor but the waveform on oscilloscope become too small? my testing design none transistor.

  41. sir we design the above circuit but its not work. Actually I can't understand the working of the circuit. I have many troubleshooting problem. Kindly mention the working of the circuit..
    Thank you

    • what frequency are you getting at the pin9 and pin10??

      …I have already explained everything comprehensively in the article, if you have any specific questions, you can put them here.

  42. Hi Mr. swagattam can i use IRF 3205 instead of the mosfet above and a Microwave Oven Transformer with its secondary removed and rewired using 10 gauge wire centre tap?

    • Hi clickbirth, I have not yet researched this parameter so I have not idea about the formula for this, alternatively you can test it by adjusting the 22k pot and then verify the resistance value across the pot for determining the value

  44. Hello Mr. swagatam I want to do this one again I have bought all the requirements now but I want to know how many volt and ahms transformer should I use to get 300watt or 500watt? Thank you sir.

  45. So basically sir what this means is that
    1)the 10k pot can be used to adjust the output voltage.
    2)even the modified sine wave inverters that employs the SG3524/SG3525 chip or even ur own SG3525 modified sine wave circuit you posted on your site earlier can eliminate the feedback transformer from the output inverter itself and all that rectification and all that will be eliminated and we can rig the SG3525 to work without all those diode rectication and the small feedback trafo,exactly in the same way the TL494 works in maintaining constant voltage under varying load conditions.?
    By the way it's Michael not Alex.

    • That's right Michael.

      Because, according to me as long as the 5.1V reference stays constant the PWM would also stay constant which in turn would make sure that the outputs voltage stays constant.

      so yes even for SG3524/3525, the principle of operation looks alike and therefore an external feedback may not be required for the corrections.

      sorry for the confusion, your questions are much identical to what Mr. Alex (another dedicated member) normally asks,,,that's why I mistakenly thought you to be him.

  46. Sir does this mean the inverter does not need feedback from the output of the inverter.?
    Does it mean that if it is a 1500w or 5000w inverter rated at 220v operating at full load it will regulate it self to steady 220v who operating at full load?

    • Mr Alex, that's correct, because the PWM is set by referring to a constant 5V generated at pin14 of the IC, once set, the PWMs will not change regardless of the output load, unless the load spec is too high and the reference 5V is disturbed due to a alarming drop in the battery voltage

  47. hello janak,

    the IC already has an internal oscillator, no external pulse is required here.

    and yes without a frequency the fets will stall and instantly burn, a frequency is the only way to keep the inverter and the fets running….

  48. hello……..mr Swagatam

    had made circuit as above ,it run well when i give pulse but when m remove pulse circuit MOSFET(IRFZ44N) start to heat

    it aslo work well in H bridge conf,

    please solve my query please….

    • Hi Franco, yes it should be 20+20 for the primary with a 12V supply, the secondary can be upto 1000 turns or even more, as per the required high voltage needs.The thickness of the wire can be about 0.2mm to 0.3mm

      Begin with 1000V and check the output level, then you can increase the no of turns proportionately to any degree until the required level is achieved

  52. Hi swataman majumdar,
    can i build the circuit before on breadboard or this is a problem?
    i wanted to swing the IC to high frequency and so i think to replace the resistor 22k + 4,7k with an fixed resistor 3,3k and the capacitor of 1 nf with another of 4700pf.
    in this way the IC have a frequenzy (sawtooth) of 70khz about.
    How can i do for building an toroidal transformer that work with 70 khz about?
    the idea is to have an high voltage in output using a smaller toroidal transformer.
    Thank you so much for your time.
    kyu9971

    • Hi franco, yes you can make the trial version on a breadboard, no issues.

      initially you can try around 40 turns of 1mm wire on your torroidal transformer, you can reduce or increase number the turns proportionately further, in order to achieve the intended high voltage level

  54. Hi sir, thanks for work done but am just requesting you to design for an INVERTER circuit diagram using IC SG3524 where the output voltage will be proportional to the input voltage.
    Meaning if the output will be constant on a certain range of LOAD regardless of the dropdown of the input voltage upto a certain level. Thanks

  56. Hi swagatam majumdar,
    is possibible to use this circuit for get an output high voltage DC (about 310vdc), doing swing the tl494 to high frequency and using an ferrite core transformer?
    thank you

    • Hi franco, yes surely the design can be used for generating high voltages to any desired levels.

      the transformer will have to be designed as per the 310V spec for enabling the production of this voltage.

    • you will need to check the output voltage from the transformer and simultaneously adjust 10k preset until the voltage is adjusted to the nearest normal level.

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