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## Modified Sine Wave Inverter Circuit Using IC 3525, with Regulated Output and Low Battery Protection

The post explains a simple modified sine wave inverter circuit using a single IC SG 3525. The circuit is equipped with a low battery detection and cut off feature, and an automatic output voltage regulation feature.

The circuit was requested by one of the interested readers of this blog. Let's learn more about the request and the circuit functioning.

The request:

"hello sir Swagatam, i will be grateful if you can help me on Pure Sine Wave Inverter circuit using ic sg3525 with mosfet and a center tap transformer."

The Design:

In the previous post I discussed the pin out functioning of the IC 3525, using the data, I designed the following circuit which is though quite standard in its configuration, includes a low battery shut down feature and also an automatic output regulation enhancement.

The following explanation will walk us through the various stages of the circuit, let's learn them:

As can be witnessed in the given diagram, the ICSG3525 is rigged in its standard PWM generator/oscillator mode where the frequency of oscillation is determined by C1, R2 and P1.

P1 can be adjusted for acquiring accurate frequencies as per the required specs of the application.

The range of P1 is from 100Hz to 500 kHz, here we are interested in the 100 Hz value which ultimately provides a 50Hz across the two outputs at pin#11 and Pin#14.

The above two outputs oscillate alternately in a push pull manner (totem pole), driving the connected mosfets into saturation at the fixed frequency - 50 Hz.

The mosfets in response, "push and Pull the battery voltage/current across the two winding of the transformer which in turn generates the required mains AC at the output winding of the transformer.

The peak voltage generated at the output would be anywhere around 300 Volts which must adjusted to around 220V RMS using a good quality RMS meter and by adjusting P2.

P2 actually adjusts the width of the pulses at pin#11/#14, which helps to provide the required RMS at the output.

This feature facilitates a PWM controlled modified sine waveform at the output.

Automatic Output Voltage Regulation Feature

Since the IC facilitates a PWM control pin-out this pin-out can be exploited for enabling an automatic output regulation of the system.

Pin#2 is the sensing input of the internal built in error Opamp, normally the voltage at this pin (non inv.) should not increase above the 5.1V mark by default, because the inv pin#1 is fixed at 5.1V internally.

As long as pin#2 is within the specified voltage limit, the PWM correction feature stays inactive, however the moment the voltage at pin#2 tends to rise above 5.1V the output pulses are subsequently narrowed down in an attempt to correct and balance the output voltage accordingly.

A small sensing transformer TR2 is used here for acquiring a sample voltage of the output, this voltage is appropriately rectified and fed to pin#2 of the IC1.

P3 is set such that the fed voltage stays well below the 5.1V limit when the output voltage RMS is around 220V. This sets up the auto regulation feature of the circuit.

Now if due to any reason the output voltage tends to rise above the set value, the PWM correction feature activates and the voltage gets reduced.

Ideally P3 should be set such that the output voltage RMS is fixed at 250V.

So if the above voltage drops below 250V, the PWM correction will try to pull it upward, and vice versa,  this will help to acquire a two way regulation of the output,

A careful investigation will show that the inclusion of R3, R4, P2 are meaningless, these may be removed from the circuit. P3 may be solely used for getting the intended PWM control at the output.

Low Battery Cut-of Feature

The other handy feature of this circuit is the low battery cut off ability.

Again this introduction becomes possible due to the in built shut down feature of the IC SG3525.

Pin#10 of the IC will respond to a positive signal and will shut down the output until  the signal is inhibited.

A 741 opamp here functions as the low voltage detector.

P5 should be set such that the output of 741 remains at logic low as long as the battery voltage is above the low voltage threshold, this may be 11.5V. 11V or 10.5 as preferred by the user, ideally it shouldn't be less than 11V.

Once this is set, if the battery voltage tends to go below the low voltage mark, the output of the IC instantly becomes high, activating the shut down feature of  IC1, inhibiting any further loss of battery voltage.

The feedback resistor R9 and P4 makes sure the position stays latched even if the battery voltage tends to rise back to some higher levels after the shut down operation is activated.

Parts List
All resistors are 1/4 watt 1% MFR. unless otherwise stated.

R1, R7 = 22 Ohms
R2, R4, R8, R10 = 1K
R3 = 4K7
R5, R6 = 100 Ohms
R9 = 100K
C1 = 0.1uF/50V MKT
C2, C3, C4, C5 = 100nF
C6, C7 = 4.7uF/25V
P1 = 330K preset
P2---P5 = 10K presets
T1, T2 = IRF540N
D1----D6 = 1N4007
IC1 = SG 3525
IC2 = LM741
TR1 = 8-0-8V.....current as per requirement
TR2 = 0-9V/100mA
Battery = 12V/25 to 100 AH

The low battery opamp stage in the above shown schematic could be modified for a better response as given in the following diagram:

Here we can see that pin3 of the opamp now has it's own reference network using D6 and R11, and does not depend on the reference voltage from the IC 3525 pin16.

Pin6 of the opamp employs a zener diode in order to stop any leakages that might disturb pin10 of the SG3525 during its normal operations.

R11 = 10K
D6, D7 = zener diodes, 3.3V, 1/2 watt

•  Stumble

1. hi swagath ,
frequency =1/(rt*ct)

as per this i think c1,r2 and p2 does not satisfies the 50kfz

1. The actual formula is

F= 1/Ct(0.7 Rt + 3 Rd)

You may calculate it using this formula :D

2. hi swagatam what is Rd on your formula

Regards.

3. Hi Roger,

Rd is the discharge resistor value, at pin#7

2. can you please design me a 12v 2amp solar charge controller with cheap parts good and reliable
with lvd and full charge cut off
thanks

1. You can build the following circuit, eliminate the IC555 section:

3. Hi Swagatam,

what is the difference between 3524 and 3525?

for now i have an inverter using 3524.

which is much better to work with all appliances?

Regards,
Mike

1. Hi Mike,
It's the waveform that matters while operating sophisticated equipment on inverters.

Both the ICs are quite similar and provide identical waveform optimization facility, not much difference.

Regards.

2. Hi Swagatam,

what is the waveform of 3524 can produce? is it capable for modified sinewave?

Regards,
Mike

3. Hi Mike,

According to me, a 3525 is capable of producing crude sine wave modification or imitation, because it produces single controllable square wave block from each of its o/ps.

My designs which involve IC 555 of 556 are perhaps more sophisticated than the a 3525 circuit.

Regards.

4. which mosfet should i use for a 40 amp battery (all 3 mosfet or only q4 ?)

1. only Q2,Q4, make them IRF540N

5. If R3, R4 and P2 are removed, will D5 be connected to only C4 and pin 2 of IC1?

1. Yes, that's correct....the PWM optimization then only relies on the adjustment of P3, and the output voltage conditions.

6. Hi Swagatam,

What is the use of P5 and the value of it?

Regards,
Mike

1. Hi Mike,

It's for setting the low voltage cut off threshold of the battery.

P4 is for latching the circuit once the low voltage situation is detected.

7. Hi Swagatam,

What is the use of P5 and the value of it?

Regards,
Mike

1. P5 = 10K preset

2. Hi Swagatam,

Thanks for the quick response.
I still have a question.
P5 is connected to the live positive, before the switch?
what about the pin#7 of 741, is it connected before or after the switch?

Regards,
Mike L

3. Hi Mike,

Thanks for pointing out the issue!

Actually all connections that belong to the positive supply must be connected after the fuse..... P5, pin#7 both has to go after the fuse in the positive line.

Regards.

8. hi swagatam,
i have a question but it is not related to this topic. but i don't what topic it belongs either. sorry for inconvenient. my question is..
can a stepper motor use as a fan? (For hot days)
if so how to power it up?
how to make it powerful? (Winding, current)
Does it takes a lot of electricity for using it, if made one?

Thanks again,
Thila.

1. Hi Thila,

If your question is regarding a DC operated fan then I think the use of an ordinary permanent magnet motor would be more efficient.

I am not very sure about other kinds of motor efficiency levels.

Regards.

9. Can i connect a 40 amp battery to my ups that originally had a 7 amp battery, not gono use to to charge battery just back up
thanks

1. If both the batteries have same voltage specs then there's no problem.

10. The TR1 8-0-8v is not available at my nearest market.can i use 9-0-9v.
Thanks and Regards.
s.m.mohiddin.

11. Hi Swagatam sir!
This is Jithendra, my problem was I just assembled an inverter circuit which is taken from google search and It's components are C1061 & 2N3055 transistor's. In my local market step-up transformer is not available. The rated power for inverter is 500Watts. Can I use a step-down transformer with reversed instead of step-up(i.e., taking secondary as I/P of inverter and primary as O/P of inverter)? If so please give me parameters of the transformer...

1. Hi Jithendra,

Yes you may do that! If the supply is 12V battery...use 9-0-9V/30 amp/220V transformer

12. Hi Swagatam Majumdar,
amer ekta 600va ups ache.
ota on korlei aktana bip diche.
ki kore ami thik korbo plz bolte parbe?

1. Hi Probuddha,

I am sorry without seeing the system practically it will be difficult to troubleshoot the issue....

2. i have a ups transformer.
no.- 080-48124-02 GP 0620
class b viking B-2
E210832

what the input & out put wire.
can i use this transformer for simple ups making....

3. it's difficult to identify through code nos. you will have to identify all the taps and check the respective voltages and wattages by multimeter...only in that way you would be able to know its specifications.

4. Primary
--------------------------
Black 230Vac
Blue
Yellow 230Vac

Red 17.7Vac
Brown 17.7Vac
--------------------------
secondary
--------------------------
Blue 15Vac
Red 7.5Vac
Brown 15Vac

5. sorry, I cannot identify through color codes....no idea

6. ok, that's fine i didn't notice the given voltage ratings.....you will have to find the center tap, that is the 7.5-0-7.5V taps, find these taps, then you can use it with the above circuit design.

13. I want to make a 1000 watt inverter, if you could be a series of 1000 watts?

1. you may modify the above circuit for getting 1000VA, just add three more mosfets in parallel with the existing ones, use IRf540N mosfets.

2. Hi Swagatam,

Can i use irfz44n?

Regards,

3. Hi Mike,

Yes you may use it....

14. Hai Sir,

While Inverter output is connected to LCD monitor its output is increased with out controll.Please give any soloutions

Suresh

1. Hi suresh,

please provide with all the details of the inverter circuit....

15. What modification will l make in the SG3525 IC Inverter circuit to achieve 3kVA. l have about 4kVA transformer of 24-0-24.I planned to used 16 mosfets with heavy heat sink.What other modifications should l make on the circuit to achieve the 3kVA power output. Thanks, Ladipo K.O, Akure,Nigeria

1. That should be enough according to me, but the battery will need to be a 24V also. Use a 7812 IC for supplying the Vdd voltage to the ICs.

16. How many mosfet for 750-1000watt???....sir

1. it depends on the rating of the devices, if it's high then you can use less numbers in parallel, and vice versa.

17. Sir,
I have an inverter transformer 750w can i use it as TR1 ,0-12v/500ma transformer as TR2.

1. Yes if the taps are similar to the diagram, they can be used.

18. Sir,

it is possible to connect a buzzer across pin#6 & ground
of IC 2.

1. Yes you can do it.

19. I was thinking if this modified sine wave inverter could be converted to a pure sine wave version by removing the dead band reistor on pin(7) and connecting a 555 square wave oscillator with reverse diodes to the 2 MOSFET gates as in your previous circuits. Just wondering if it would work.

1. yes, it can be done.

20. Hi Swagatam.
I was just wondering if one could convert this modified sine wave inverter to a pure digital sine wave inverter by removing the resistor on pin "7" and connecting pin "7" directly to pin"5" and secondly using a 555 square wave oscillator with reverse diodes connecting them to the gates of the 2 mosfets driving the power transformer.

1. that 's worth trying.....no issues.

21. Hi Swagatam, please tell me is the C1 a non polarized or electrolytic and If R3, R4 and P2 are removed, will D5 be connected to only C4 and pin 2 of IC1. what about the pin 16 will it be connected too?

1. C1 is non polar.

yes D5 will be connected to pin2 in that case.

pin16 will remain connected to C5 only.

22. Hi Swagatam,

I've built DC SG3525 inverter 22KHZ for my CDI project without dc output voltage regulation. I want to incorporate your voltage feedback circuit and connect to pin2. I will removed R3,P2 and R4.

I want also to eliminate noise of 22 khz noise on +12V supply. Already place 6.5uH between center tap of TR1 and +12V battery. Can you suggest resistor and capacitor value as rc filter circuit connected on Drain of T1 and T2 and center tap of transformer?

1. Hi Rleo,

I don't think 22khz frequency would affect the 12v supply in anyway, because it's too high, and will be virtually inaudible.

the resistor/capacitor values will need some calculations in order to obtain the correct values.

you may refer a woofer passive cross-over network circuit, it would give you an idea how to cancel out the noise.

23. Hi sir, I am very thankful to you and I really like your work. Please sir I have build an inverter circuit and it can not power my computer and amplifier with 1000w. Please sir can you give a circuit which power my computer and the amplifier. I have also seen that most of your circuit using mosfet and it is not very easily to get mosfet in Ghana, please sir can you build a circuit for me with alley transistors please.

1. Hi Etoh,

Thanks! Making a 1000VA plus inverter circuit using transistors would be difficult and hugely bulky, you would require probably 25 to 30 power transistors connected in parallel with huge wirewound resistors connected to their bases and emitters.

Presently i do not have a transistor based 1000 va inverter design, if I get one i'll surely publish it in this blog.

Regards.

24. Hii swagat,

its great one.

i have some doubts.

1) what is the power of this inverter if i make as per given diagram.

2) If i have to make 1000 W, as per ur advice I have to use 4 mosfet at both sides (IRF540N) in parallel Right?.. parallel means the connection will be D to D, S to S, G to G ?..

3) for 1000 W can i use 2 IRF3205 at both sides in parallel.

1. Hi Mahroof,

Thanks

1)power will depend on the current capacity of the transformer
2)that's right.
3) yes it can be used.

25. Hi sir i need a 100 mH inductor, how many number of turns of coil is required over ferrite rod?(any special type of coil to reduce number of turns?)
also my pwm output is 2V but when supplied to mosfet gate the mosfet does not conduct,how to amplify or increase pwm output to 5v...
Thank u
regards

1. Hi Gayatri,

which circuit are you referring to??

the above circuit or some other circuit?

2. sorry not the above circuit, a general question

3. I need to see the circuit diagram, only then i would be able to comment....

26. hi sir i need to know how the battery will be recharged and i have an 12 volt transformer does it work for t1

1. Hi Bharath,

the circuit does not include a charging facility, you will have to incorporate a separate transformer for charging the battery.

27. The output from CD4047 pin 11 and 10 is 2 V,but mosfet does not conducts(http://www.google.co.in/imgres?imgurl=http://project.irone.org/wp-content/uploads/2009/04/simple-inverter-dc-to-ac-using-cd4047.gif&imgrefurl=http://project.irone.org/simple-dc-to-ac-inverter-using-cd4047.html&h=294&w=628&sz=7&tbnid=-qDxwmGEdqcdQM:&tbnh=57&tbnw=122&prev=/search%3Fq%3Dcd4047%26tbm%3Disch%26tbo%3Du&zoom=1&q=cd4047&usg=__9luCIPBRzCzgbhgYr_aj2c8yRZw=&docid=KRCi-scTIHhtgM&hl=en&sa=X&ei=fQ5KUZiaAoXXrQfSp4DIAw&sqi=2&ved=0CC4Q9QEwAA&dur=278)

1. Pin10 and 11 will provide the average voltage of the supply depending on the duty cycle, normally duty cycle will be 50%, so the voltage should be around 6V when the supply input is 12V.

2V indicates a faulty circuit or IC, it should be 6v.....at 2v the mosfets will never conduct.

check the connections properly.

2. Thank you sir!!

28. Hi Swagatam,

Great circuit, thanks a lot!! I need your assistance thou with it,
Which components to eliminate from it, if I want to feed it from signal generator with square wave. The Signal gen will be arduino MCU. I need it
to program variable frequencies on your final schematic.
Should I eliminate components R1, C1, P1 and R2 ? and where to feed signal in ?
Regards,

Thomas

1. Hi Thomas,

Thanks!!

Though I am not absolutely sure, pin#3 can be fed with an external oscillator signal, rest of the components in the circuit will remain as it is.

The signal fed at pin#3 will force the output to synchronize with its rate.

29. Hi Swagatam,

Ok, then which part of the original circuit is responsible for oscillation ?
I believe it is R1 C1 network ? So, if I will connect ext oscillator, let's say to the negative rail and positive between C2 and C3 (is this correct location thou ?), will it not interfere with original oscillating network ??

Regards,

Thomas

1. Hi Thomas,

In the datasheet it's only given that pin#3 receives external clocks for synchronizing the output, and many ICs can be tied with this common external frequency for generating identical outputs.....you may try it out practically.

parts at pin5 and pin6 are responsible and determine the internal frequency of the IC so you may keep initially pin#6 connected to ground via a 0.01 capacitor, might just work.

30. hi, great circuit I'm intended to design it @1kW with 2 irfp150 and 3 batteries (36.V) also i'll will try somehow to use the reverse AC in the transformer to charge the battery while circuit is off , but i see that the 741 power (+ and -) isn't connected directly, so can i connect them to battery? or another power source is needed? also can i use any op-amp or it must be 741? sorry i hate op-amps, specially that 741!

also can i use current sense transformer in parallel with output and send it's output to pin 10 to provide overload protection?

thanks for such great circuit

1. Hi thanks!

the 741 supply points can be connected to the existing battery poles.

any voltage at pin10 will be taken as high, so i think connecting sensing transformer output to pin10 won't work.

Regards

31. Hello sir,
Can 12-0-12 be used instead of 8-0-8 tr.can it gives any extra effect on mosfet. Can 0-12 500ma will be used instead of 0-9 100ma tr.
Thanks...

1. yes both of them can be tried..

2. Thanks for ur kind reply sir,
I m trying to make this circuit.i need some help on this,
1-Can all the 10k preset it replaced with 4.7k preset.
2-i m using two 474k/250v ppc type in parallel instead if 1uf/50v.does it is ok.
3-will u suggest to put gate to source resistance for safty of mosfets
Thanks

3. Hi Avijeet,

1 yes 4.7k can be used in place of 10k
2) 2nos 474 would become bulky but will work
3)you can employ diodes for safety if you feel so, although all modern mosfets have built in diodes

4. Thanks for ur quick and kind reply sir,
I will be back to u after completing this circuit and surly share my experience on making of this circuit.
By the way i had one more query- can a 12-0-12 step down transformer work in reverse instead of 12-0-12 stepup transformer.
Thanks

5. Hello sir,
I had made The above circuit with ur valuable suggestions. I think i had made it correctly and it is also giving me the output.but i think it need some more attention of yours.when i made the circuit it is not giving me any output.after paying lots of attention on ur article i came to realize that pin#10 of ic1 is getiing logic high from pin7 of ic741. My 741ic is giving 1.9v when it is at the logic low condition due to which its make my 3525 ic always shutdown. After disconnecting the connection My ic1 starts to give output.
Thanks for kind help and support.
Tr2:0-12,750ma
Preset 4.7k
Opamp: ua741
In above circuit two r9 are shown i think r9 with LED shuolud be 1k and r9 across #6(741) and preset should be 100k

6. Hello Avijeet,

you can connect a 3v zener in series with the output of the IC and pin#10, this will stop the flow of the parasitic voltage.

yes, the R9 values according to you are correct.

7. hello sir,
i had made the connections as u said with 3v zenner diod
but it still giving me 1v of output.
i had tried with more havy zeener diods and now 5.6v zenner is giving me the desired output.
thanks for ur great support

8. you are welcome!

9. Hello sir,
Hope u r fine there
Thanks "

10. Hello Avijeet,

That's very interesting, congrats on that!

I am actually not sure about that extra tap....may be it was used as a feed back for the voltage control stage in the old inverter.

It would be better to use an external SMPS unit for charging the battery that would keep the wiring simple and compact.

However, I have discussed one such circuit here, you may refer to it:

11. Thanks sir,
So u r suggesting me to leave that extra tap unused.

The article u had suggested for charging battery with same inverter trafo consists a extra circuit for energizing two dtdp relays.which on energizing diverts trafo taps and charge battery via a single diode 5402 and a 47000uf capacitor.
Sir i want to ask u that is it a good idea to charge a battery directly from 0-12 taps via 5402 and a high value capacitor specially when the battery is of good quality tubular type which are specially used for inverter now in this days.

In the charging process we are using only half winding of lower Voltage side of trafo and assuming that my trafo is of approx 700watts then it should be about 30amp trafo. So when we are using half winding is 30Amp also becoms half i.e.15amp. Reason behind asking this question is that i want to use a 150ah battery for charging and according to ur some previous articles related to charging of battery u had suggested to keep minumum trafo 1/10th of batteries ah.
And If it remains 30amp on using half winding should it give any harm to 150ah battery on charging
with it.
And at last,u had suggested me to put an external smps circuit for charging purpose.would u suggest me any smps circuit for charging of a 150ah battery

Thanks for ur great support sir
U had supported me alot by solving my queries with ur tremendous knowledge.
I don't know how to thank u.
Thanks.
God bless u sir.

12. You are welcome Avijeet!

15amp would be OK for 150AH, but the shown method is crude and not appropriate since the voltage would inadequate for charging the battery, so I think you should go for a separate SMPS unit for charging the battery.

designing a 15amp smps would be difficult and complex, it would be better to buy a readymade unit.

13. Thanks for ur reply sir,
Can u give me some idea related to specifications of SMPS. i.e.what type of smps i have to search in my local market for charging 150 ah battery.

Thanks

14. It should 2V higher than the battery voltage and current should be 1/10th of battery AH

15. Thanks sir,
U had discussed two different article related to charging of high ah battery in previous post of ur blog
1-high current transistor tip 36.
and
2-how to make high current 10 to 20 amp automatic lead acid battery Charger.

Can u suggest whether it would be good or not to use one of them For charging 12v 150ah tubular type battery for my inverter.

Thanks

16. The 10/20 amp circuit would be easier to make and use, so you can try that circuit...

17. The circuit suggested by me is better because it incorporates an opamp.

By the way the ink provided by you is not an smps, it's a simple transformer PS.

32. hello sir,
thanks for ur help
sir actually i not able to found such high amp smps for charging my 150ah battery in my local market. so, i have the only way to use my inverter trafo in reverse for charging. sir want to clear some doubt with u:
1>assuming my trafo is of 12v 30amp, so when i use its low voltage tap 0-12 for charging leaving one 12v tap unused i.e we are using half winding. so here i want to know that is its amperage also becomes half i.e 15amp or it remains 30 amp.i am asking this because i have to recharge my 150ah battery so if its give 30 amp will it harm my battery.
2>i had seen some inverter circuit using two tny612 mosfets. is its related with charging of bateery.
3>in searching smps circuit in net i found an ic "uc 3906" specially desigend for charging related porpose of battery. will u give some valuable information on it if u have any.

thanks

1. Hi Avijeet,

1) yes using half winding will also make the current half according to me.
2)It would be difficult to say about tny612 circuit without seeing it practically.
3)UC3906 is a customized chip specially built for lead acid battery charging application, if you can get it in the market, would be worth building the circuit.

you can check the datasheet here:

1. Hello sir,
As i had told u earlier that i had got a old inverter transformer which is about 7 kg in weight and shopkeeper told me that it should be around 700 to 800 watts.when i tested it by putting its higher voltage side in mains 230ac it is giving me output of 9-0-9 on its lower voltage side.so, i want to know that according to u what should be its amp rating approx and how could i use it to charge a 12v 150ah battery

Thanks

2. Hello sir,
I m not able see ur reply

3. Hello Avijeet,

You can divide the assumed wattage with 18v for knowing the approximate current.

4. You can use this circuit for making a simple current controlled battery charger circuit:

Refer the comments for understanding regarding the selection of the current sensing resistor.

5. hello sir,
thanks for ur valuable suggetion, i had some query related to ur sugested cuircuit for charging
-->can i use this circuit as it is for charging purpose by putting battery on load side via diode and capacitior bridge.
-->is i had to draw 15amp from lower side of trafo for 150ah rating battery that means it draw 1.5amp to 2amp(approx)at higher side of trafo.(please correct me if i m wrong)
-->after putting reqired r2 for limiting current will this circuit stops power supply to trafo if trafo draws more current than its set limit or will this circuit allow only the set limit of current to trafo continuosly whithout stopping power supply to trafo

thanks

6. Hello Avijeet,

The simple way to check the primary current is by connecting a series AC ammeter at the primary side and connecting a 15amp load at the secondary side.

You can use automotive lamps for making a dummy 15 amp load.

After this the value of R can be calculated by the formula R = 0.6/prim current on ammeter.

33. swagatham how to measure the frequency of an inverter(using multimeter or how?

1. select the Hz or kHz range and connect the prods directly with the output of the inverter.

34. Hi sir, thanks for your dedication on this, just a humble request, give us a PCB for this project
Thanks
Darlington

1. Thanks Darlington,

I'll surely try to include it when I have time.

35. Hi sir
I it possible to build a 2500watt inverter with the above circuit diagram? If yes
What do i need to add
Thanks best regard.

1. Yes it is possible, you will need a supply of 100V and a transformer rated at 25 amps.

36. hi sir
i have assembled the given circuit but i amnot geting the proper output it is near around 50 volts is showing what may be the problem sir would help me sir waiting for your advice and suggestion

1. Hi Rupesh,

Disconnect Pin#2 of the IC from P2 and D5 and then check.

37. hi sir
i need your help to get the proper output from the given circuit
i am only getting 50 volts

38. Hello Sir,
Can I use a Lead acid 12v 7AH battery in this circuit?? if not,can you suggest me a inverter circuit with output 220V,50Hz
with lead acid battery?? I need very small wattage like 50watt for my project.

You can try the following design:

39. hi Swagatam,can i use this circuit to make a 2kw inverter.if yes; how many mosfets i need to put more.and what will be the change in circuit.
thanks

1. for 2kva you will have to use 50v suppy (battery) otherwise the wiring and the transformer will become too heavy.

with 50v, you can use IRF3205 mosfes over each channel, but make sure the IC gets a regulated 12V

40. Namastay Swagatam; do you have such modified inverter circuit which can bear a load of 1500 watt and can opperate on 24 volt.
thanks

1. Namastay, you can try the above design and refer to the previous comment above for the required modifications.

41. thanks for reply;but i want to use it with my solar array and i have only two 12v batteries.therefore i want to operate it on 24v.no matter if it can bear 1500 watt load only.but want to operate it on 24v.is it possible.and which wiring i need to make heavy for this.please also mention the changes in the circuit.i already tried this circuit on small loads but want to take risk for 1.5 or more.

1. 1500/24 gives 62, means all connections and wiring must be rated for handling above 65 amps, that's huge current.

No changes would be required in the circuit, just make sure to use a 7812 IC for powering the ICs, because the ICs won't tolerate 24V.

42. sir Nmastay,can you check it and provide information how to connect it with your project to get pure sine wave.if it is possible then please also mention how to merge it in this project

1. Hello Ravi,

I'll be posting a related inverter circuit soon in my blog which will be exactly as per your specs.

43. Hi sir lots of thanks for the reply, as you said to disconnect pin#2 I have disconnected and checked but after that also I am getting only 50v output what may be the other problem sir i have check the connection also everything is correct as per the circuit diagram

1. How much voltage are you getting at the mosfet gates? It must be around half that of the supply voltage, meaning if the battery voltage is 12, the gate voltages should be 6V...please check it.

Aso, Connect 1N5402 diodes across drain and source of each mosfet.

44. Hello sir,
Can u give some idea to use homemade optocoupler(ldr and led) for feedback voltage correction section instead of trafo for less spacious circuit and for convenient
Thanks

1. Hello Avijeet,

I'll try to include it in my site soon, may be within next few days, if i forget do remind me please.

2. Hello sir,
Have u got some success for inclusion of optocoupler in voltage feedback section.

sorry to disturb u

3. Hello Avijeet,

see the example in the second circuit given in this link, although the circuit is different from the 3525 IC, but you can get an idea from it:

4. Thanks sir,
Accoding to ur referred link i had came to understand that i had to connect led leads directly to trafo taps via resistor. But i m little confused where i had to connect ldr leads.directly after diode bridge of current sensing trafo or i had to make some major changes in above schematic

Thanks

5. You will have to connect the LDR via a voltage divider network to pin#1 of the IC, please see the link at the beginning of the article, and read how the pin#1 functions for the IC3525

45. can this circuit work for 3000va inverter

1. yes it can work at 3kva

46. Hi sir can i make a turns to provid 9v insite Tr1for feedback, that becomes a single transfomer.
From Salman

1. yes if it's feasible then it would work

47. Hi Swagatam i need to biuld 5kva 24v wich gauge of wire is suppose to use for primary and secondary of TR1. I need your help from salman.

1. Hi Salman, I am not sure about the calculations, so cannot confirm.

48. hi can the circuit run motors thank u

49. can i use de same transformer to charge when i modify it with a relay thank u

1. No....... the trafo voltage is rated lower than battery voltage, so cannot work both ways.

50. can i use a upto coupler instead of de sensing transformer and how thank u

1. you can use a LED/LDR opto

51. hallo say de trans is 220v and 11--o-11v plus 13v can i use de 13v charge de battery

1. 14V is the optimal requirement, 13V will charge 50% only.

52. How many voltage is good for power supply of 5KVA.
Salman

1. If you can manage voltage equal to the output that would be most ideal, use as many batteries you can in series to increase the voltage.
higher the voltage easier the circuit becomes to handle.

53. i want to make an inverter driving 2 flat irons how many watts should i make and de logic about de transformer thanks

1. pls specify watts of iron??

54. Good job Mr Swagatam, but I don't understand how voltage equal to the output. Thank's

1. if it's 220V AC required at the output, using 220V DC at the input would give best results

55. can i use 2 flat irons on a3kva inverter using this circuit thank u

1. i did not understand ur question

56. hi how many watts can drive 2 flat irons thank u

1. what's the wattage of your flat irons?

57. many thanks for this circuit.

can i use TR 12-0-12 center tap? if answer is No can you explan please?

1. thanks! yes you can use it.

2. thank you for quick replay

58. hello Mr swagatam i love your circuit . What would happen if we use a higher value for r1 which controls the dead time. I built a similar circuit but pin 4 and 5 are gone to ground but i see u use them so I figure this would maybe give us a difffirent effect. Thank u for ur support

1. hello joel, yes R1 can be tweaked for fixing the dead time between the outputs of the IC

59. Hi Swagatam, nice circuit and I was wondering how can the circuit be modified to utilise opto-isolator for output feedback instead of transformer?

1. Thanks! you can refer to the last diagram shown in the following article:

See how the opto-couper is configured with the PWM adjust pin of the relevant IC....the same principle could be followed for the SG3525 circuit also since it too has a PWM adj pinout

60. Sir are the ics SG3524 and SG3525 same ??
I need a little modification in the present circuit by introducing an overload protection feature ( by exploiting the shut off feature of the pwm ic ). COULD YOU PLZ HELP ME SIR??????

1. Yes the two ICs are interchangeable, you can use 3524.

The overload feature is already included in the above design using the opamp IC2.

61. You mean, the ac out falls to zero automatically when load connected to the inverter rises above the maximum limit SIR ?????

1. yes, it will go ON/OFF continuously at the rate of microseconds and will result in a constant output

62. Dear sir,
Can i use a 24 V battery with a 15-0-15 power transformer to generate 230 V ac out with this circuit ? Which are the modifications to be carried out ?

1. Yes it can be used but you will have to adjust the PWM setting for getting 220V at the output before connecting any load

63. Sir can you please point out the changes in pinout connections occured in replacing ic SG3525 with SG3524. Some pins are seen different such as the 8th pin in 3525 is for soft start ,but it is absent in the other. Similarly other some too. If you are not thinking i am disturbing you much, please help me. I am not supposed to burn my ics intentionally. That is why....

1. Arun, you may refer to these two datasheets and compare the pinouts. If you find it difficult then you can try finding some other inverter circuit which uses SG3524, i think that will be much safer for you.

http://www.ti.com/lit/ds/slvs077d/slvs077d.pdf

64. Here can i use a 12-0-12 V/ 500 mA transformer as a current sensing one ( T2 ) SIR ?

1. yes you can use it.

65. Hellow sir, this is arun again. I saw your last reply just know. Thanks very much. I am expecting the reply for all other pending comments posted by me as soon as possible. Now i am gonna design the circuit, but i have only a 230/15-0-15 power transformer with me. So in order to satisfy the pwm requirements i may have to use battery voltage of atleast 24 V. So i am connecting two 12 V 20 Ah batteries in series. Can you please point out the necessary modicications needed for this ???

1. Hi Arun, The ICs should be supplied from one 12v battery (center connection of the battery series), while the trafo center tap should be applied with the 24V positive of the battery, all the grounds then become common (battery negative)...pwm pot should be carefully adjusted to produce 220V at the output without load.

66. Hi sir! Pls can you explain to me how the p5 is set, and where should the voltmeter be placed? Is the arrow from pin2(741) to p5 connected to ground(p5)

1. p5 is a preset whose center lead is connected with pin#2 of the IC 741.

for setting p5, apply 11v so that it reaches to both the ICs then adjust p5 until the led at pin6 of 741 just lights up.........keep R9 link disconnected while doing this, and reconnect it back once the setting is completed.

67. Sorry sir, i have only just noticed the instruction about posting links with comments. But i can't sir. Since i am commenting on this blog using ma phone, i willn't be able to make use of image hosting sites since it takes much time due to larger failure rate. So i am requesting you to reply ma comments without posting links in ma comments

1. Sorry Arun, i cannot allow external links in the comments, by the way what was your previous question?

68. Forgot to say you sir. I have used mosfets IRF540N instead of transistors in my schematics. Can you make a judgement now ?

1. you mean in the above shown 3525 circuit?....yes it will do.

69. Sir, can i use any type of optocoupler with higher watt ( of the order of 300 W or more ) pwm inverters like this instead of the sensing transformer ?
I have a one C1010 which is named as a photocoupler in its datasheet. Can i use it for 300 W inverter ? How will be the connections look like ? And if i am not able to use it, could you plz help me in making a one myself. I have and LDR a few of LEDs with me

1. Somasundhar, an photocoupler will not produce proper results, you will have to handmake an LED/LDR opto coupler and couple it with the circuit.
The input to the LDR will need to be dropped through suitable potenial network.

You may refer to the last diagram provided in the following post for knowing more about the connections:

70. Sir, i have tried the basic circuit of inverter using ic CD4047 and IRF540Ns to check the functioning of a simple inverter. Eventhough i got little brightness in the 100 W bulb as before. Since my analog voltmeter and digital version got damaged while measuring the ac voltage, now i am aftraid of connecting a new one there. So how can i measure the ac voltage without damage to the new multimeter or is there any othet means exist ?
I think very little voltage is produced , thereby little brightness in bulb. So what i have to do sir ?
I have checked the battery voltage using a car headlight lamp which showed maximum brightness. So no confusion about battery voltage. Then what may be the real issue ? Transforner is 300 W with 4 secondary taps and 5 primary taps. I have used 1-3 taps also checked 1-2 taps of ac terminal being the 2 and 3 taps of secondary connected in common.

1. Arun, you should have selected the 1000V range in the multimeter for checking the inverter output, it's always good to use a higher range than the expected output.

connect a 10amp DC ammeter in series with the battery to check how much current your circuit is consuming with a 100 wat load.

It should be around 100/12 = 8 amps, if it's not giving this much amps would mean that either your mosfets are faulty or your trafo is not correctly rated.

71. Sir can i use KA3525 in place of SG3525 ?

1. yes can be used....

72. Sir may i remove the P4 and feed back resistance 100K in opamp circuit and connect the reference voltage from pin#16 of ic directly to pin 3 of opamp and tweak the pot P5 to adjust the voltage at pin2 of opamp falls just below the reference voltage fed to its pin3 at the battery dropout voltage of 11.5 V ????
For what purpose actually the P4 and feedback resistance are being used here. I can get the output of opamp high when the battery voltage drops below the set voltage as by the above step. So why they are important??
I am getting 8.05 V from pin#16 of ic KA3525 as reference voltage. Any ptoblem with this sir ?

1. P4 is there to introduce hysteresis to the circuit, means once P4 is set appropriately the output of 741 will not vibrate or oscillate at the threshold level, rather become solid and shut-off completely.

You can connect a 4.7V zener and a 1k resistor for applying a reference to pin#3 instead of depending on the 3525 pin16.

It should be 5.1V at pin16

73. Sir help me. I am not getting 0 Hz frequency at the gate terminals of mosfets. On checking the circuit, i found that pin #10 of KA3525 is always driving with a positive voltage. Even the battery voltage is above its cut off, this pin#10 gets a minimum voltage of 1.6V from pin#6 of opamp, thereby causing the pwm ic to stop operating, but when it is manually connected to ground it gives exact 50 Hz at the gates. So what i have to do Sir in order to make pin10 low when battery level is not near dropout ??????

1. put a zener diode of 4.7V in series with the output of 741 and pin#10, this will rectify the issue.

cathode to 741 output and anode to pin#10

74. THANK YOU FOR REPLYING MA PREVIOUS QUERIES SIR.
This time i need your valuable suggestions in completing ma.project.
Finally i found the voltage produced at the output is exactly near to 230 V ( found using an analog voltmeter of good quality ). But the power requitement is not fullfilled. That is why i am getting low brightness in the 100 W bulb.
I am having a 230/15-0-15 power transformer of 300W rating. I have checked the taps and used the suitable primary taps which provide a 11.5 V- 0 V- 11.5 V at secondary. I am using two 12 V batteries. I got 230 V even using a single battery. ( when using two in series i got more than the normal value, but these results are occuring when the pwm feed back path is kept disconnected ). Each are rated 20 Ah. Now can you make a conclusion about my low wattage output problem ?
How to test a mosfet ?
Should i have to connect several mosfets in parallel to achieve ma 300 W range ?

1. Arun, as mentioned in one of my previous comments you should check the current consumption of your circuit.
Connect a 5 amp or 10 amp DC ammeter in series with your battery positive with a suitable load connected to the inverter output.

If the current does not correspond with the load would mean a faulty mosfet or a faulty transformer. You can use this formula VxI = wattage

Simultaneously also check the battery voltage, it should not drop, if it drops would mean that your battery is not fully charged or is faulty.

75. Sir what about ma problem ?

76. Sir will your 300 W PWM pure sinewave inverter with output voltage correction provide better result than this circuit ? I saw also an improved design on that article put forward by a reader at the end of that article using ics 4066. Will it be more sophisticated ?

77. Dear Sir, I need a modified sine wave inverter using IC tl494 with it's pin configuration & pin names. . I read your wave page regularly. Please give me it.