Help With Pure Sine Wave Inverter Schematic - Page 1
Forum section: electronics / projects

author: dtomazini
author_rank: Contributor
timestamp: December 04, 2015, 09:11:13 pm
content: Hi Guys,I'm from Brazil, friendly to digital electronic and microcontrollers (PIC, ARM, Arduino, etc...), but a completely dummy in analog eletronic, mainly using Op Amps.Recently i bought on Mercado Livre (it's brazilian auction website like Ebay) an schematic to build a pure sine wave inverter. After two build tries, i could check the seller is trickster, unfortunately.There are several diferences between layout and schematic.In the first try, i was used the schematic to build the circuit, and the result was:- Pin 15 from 4020, has 60Hz a square wave. Perhaps at this point everything is ok;- After resistor R8, has a strange signal like a sawtooth wave; I couldn't confirm if was something wrong here;- TL074 the output is satured; Something is not ok;- BC337 Q9 and Q10 are overheating and smoking. I removed the transistor R22 and R23 to keep testing the board;- BC327 Q11 and Q12 are overheating and smoking. I removed the transistor R21 and R24 to continue testing the circuit;At this point, i discover the difference between layout and schematics mainly on the TL074 pins. The non-inverting and inverting input are inverted, and in the schematics didn't exists the 220R resistor on VDD pin.After this, i went to the second try, now using the layout as base to build the circuit, having:- Pin 15 from 4020, has 60Hz a square wave. Again everything is ok;- After resistor R8, has the same signal like first try;- TL074 the output is satured; Again something is not ok;- BC337 Q9 and Q10 still overhating and smoking. I removed the transistor R22 and R23 to keep testing the board;- BC327 Q11 and Q12 still overhating and smoking. I removed the transistor R21 and R24 to keep testing the board; (i will post the oscilloscope wave captures son as possible)Checking TL074 datasheet, i found a formula that determines the gain by the result value of R10 / R8 in the first stage, and R11 / R6 in the second stage. So, that explais wy the output is satured. If the input signal is around 8V (pins 2, 6), gain around 10x, VSS in Ground (pin 11), reference in Ground (pins 3,5) , and VDD is around 12V (pin 4), the output became satured.I try to use the TL074 with the reference (pins 3, 5) in half VDD using a LM7806, however the output still satured.Please, anyone having knowledgement in analog eletronic, could help to understand if exist more things wrong ?. I couldn't understand the filter used for convert the square wave in sine wave, and the usage of TL074.ThanksDaniel

author: oldway
author_rank: Super Contributor
timestamp: December 05, 2015, 12:22:42 am
content: Nope, it will never work.You better begin all from scratch

author: station240
author_rank: Unknown
timestamp: December 05, 2015, 05:08:32 am
content: The problem appears to be in the predrive circuit (Q9,10,11,12 and R21,22,23,24). The resistors should prevent the pair of transistors from both being on. These clearly isn't working hence the smoke etc.I quick search online for H bridge circuits that use a BC337, shows they all use 1K ohm resistors.Replace R21,22,23,24 with 1Kohm 1/4W and try again, carefully.

author: oldway
author_rank: Super Contributor
timestamp: December 05, 2015, 07:45:04 am
content: Don't you understand that this schematic is a fake and that the guy who designed this schematic does not know anything in electronics ?This schematic is a bluff, a scam.And you have paid for this bullshit ?

author: oldway
author_rank: Super Contributor
timestamp: December 05, 2015, 09:17:37 am
content: This guy has copied and has modified parts of different schematics he found on Internet without understanding what he was doing.

author: DanielS
author_rank: Frequent Contributor
timestamp: December 05, 2015, 02:58:38 pm
content: The TL074 part is a common two stages integrator and if it was designed properly, the first one gives you a triangular wave while the second gives you a sort-of-sinusoidal signal that is actually x^2. But then it gets fed into inverting buffers, which makes the signal square again so that part of the circuit is pointless even if it worked properly.The rest is just a square wave driver with no dead time between the two switching banks, which means a momentary dead short across the power supply which can be softened by adding a small high current inductor between the transformer and supply to limit current rise during cross-conduction.

author: onlooker
author_rank: Frequent Contributor
timestamp: December 05, 2015, 03:04:08 pm
content: Yes, there are many things not right with the schematics in which, the least is that it is not going do sine.The tl074 should have pin 2 and 6 set to, say, 3v to have the input see the polarity switching.Worse yet, all q9 to q12 had E, C pins connected backward and in wrong location. The supposed push-poll became shoot-through and this is where the smoke came.

author: wraper
author_rank: Unknown
timestamp: December 05, 2015, 03:21:58 pm
content: Quote from: onlooker on December 05, 2015, 03:04:08 pmCE are not backwards (though made to shoot through). But this is not going to work nonetheless because of the D11 and D14 zeners (3.3V) Q11 and Q12 will remain open all of the time and hence they are frying.

author: oldway
author_rank: Super Contributor
timestamp: December 05, 2015, 03:24:33 pm
content: This schematic has nothing to do with a schematic of a sine wave inverter...Try to find what is right, not what is wrong.. there are too many things that are wrong and so few that are right.

author: onlooker
author_rank: Frequent Contributor
timestamp: December 05, 2015, 03:42:47 pm
content: QuoteThe shoot-though happens on every transition edge regardless if the zeners are there or not. Are you saying this is an acceptable way to do pre-drive? An example will be helpful.

author: oldway
author_rank: Super Contributor
timestamp: December 05, 2015, 03:51:13 pm
content: It looks like he tried to design a totem pole output driver...and he succeeded to make a transistor killer.

author: djQUAN
author_rank: Frequent Contributor
timestamp: December 05, 2015, 03:55:09 pm
content: I have seen inverters advertised as "pure sine wave" but are actually driven with a square wave with sufficient dead time through a LF (big iron) transformer and a capacitor at the output to make the output waveform more "sine-like" basically a square with sloping transitions.I guess this works on the same concept. If the driving circuitry is correct.The circuit is said to be 2500W but with only eight switching devices and 12V supply? 2500W at 12V is ~208amps. Do the math.

author: wraper
author_rank: Unknown
timestamp: December 05, 2015, 03:59:32 pm
content: Quote from: onlooker on December 05, 2015, 03:42:47 pmI'm saying that with shoot-through it at least "could work" somehow. With those zeners high side transistors never close at all. And no, CE are not backwards, if driven properly (with dead time, not bases connected together) this arrangement would work fine.

author: onlooker
author_rank: Frequent Contributor
timestamp: December 05, 2015, 04:14:46 pm
content: QuoteI guess you meant to use a "bjt half h-bridge" as a pre drive for the final half-bridge. Then, add a proper driver (x2 with dead time) to drive the 1st bridge. Would it be simpler to just use a push-poll as many ANs suggested?

author: wraper
author_rank: Unknown
timestamp: December 05, 2015, 04:18:54 pm
content: Quote from: onlooker on December 05, 2015, 04:14:46 pmThis schematic is a non working junk and there is no reason to make it better.

author: oldway
author_rank: Super Contributor
timestamp: December 05, 2015, 04:58:19 pm
content: Quote from: djQUAN on December 05, 2015, 03:55:09 pmDo the math yourself...you forget that efficiency of a low voltage inverter is far from 100%...Something as 250A is more realistic.The "big transformer" is a very expansive CVT transformer.http://www.aelgroup.co.uk/faq/faq001.php

author: donmr
author_rank: Regular Contributor
timestamp: December 05, 2015, 05:53:21 pm
content: Of course I wouldn't try to produce high voltage AC if I didn't understand basic circuits. But this one is fairly simple. It has errors and issues but the overall plan could work.The 4020s are supposed to count down the crystal to get a 60 Hz square wave.The op-amps (U5) are supposed to be a low pass filter to make the signal more of a sine wave.Don't try to probe the inputs of an op-amp, they will have only very small signals. Look at the output.These are configured for a DC gain of 10x, with a 6V input so they probably clamp to the supply rails.That's your first sign of trouble. If you read up on op-amp circuits you can learn how they work and how to compensate for input offsets and bias currents. You could learn a lot making these produce a good 60Hzsine wave.After that the power driver is supposed to step up the power to get your output. At high power levels even small errors can cause big troubles so I would not suggest building that until you can analyse the circuit and be sure you have something that should work.

author: wraper
author_rank: Unknown
timestamp: December 05, 2015, 06:08:35 pm
content: Quote from: donmr on December 05, 2015, 05:53:21 pmAnd then make that sine wave back into the square wave (CD4049).Not mentioning that you won't get any sine out of the MOSFETS without negative feedback. Nonetheless even if you could, power wasted in the MOSFETS would be just HUGE. This schematic is just useless.

author: PChi
author_rank: Frequent Contributor
timestamp: December 05, 2015, 06:16:15 pm
content: If the design is meant to drive the transformer with a square wave then to generate the sine wave it needs a Constant Voltage Transformer with many micro farads of capacitance on the output and part of the transformer core is designed to saturate (a 2.5 kW CVT transformer is going to be big). Then the operational amplifier is not required.If the design is meant to drive the transformer with a sine wave then the power MOSFET circuite needs to be a linear circuit. Not be switching circuit as shown.There are other designs available likehttp://www.ti.com/lit/an/slaa602/slaa602.pdf.

author: oldway
author_rank: Super Contributor
timestamp: December 05, 2015, 06:43:29 pm
content: Unfortunately, we can not help dtomazini with his schematic.Only some advices: put it in the trash, do not waste your time and try to have your money back.

author: onlooker
author_rank: Frequent Contributor
timestamp: December 05, 2015, 07:31:26 pm
content: True, the OP is better off to start from new. A randomly googled schematics is likely to be better. Pure sine will be more complicated. The OP may also want to look into purposely made driver IC's and/or consider the approach of class D amplifier.

author: dtomazini
author_rank: Contributor
timestamp: December 06, 2015, 12:41:58 am
content: Thanks to Everybody!.Here's the oscilloscope capture from:CH1 - 4020 pin 15 - Square wave in 60Hz;CH2 - between R8 and TL074 pin 2 - sawtooth wave;CH3 - between R5 and TL074 pin 1 - strange wave;So, unfortunately it's a bad news. The main problem isn't the money wasted to buy the schematic, but the money and time wasted to buy the components, the transformer, and the circuit board construction.A few months i was looking for a schematic to build this inverter (this inverter is part of my project to use solar power), and found two schematics that could be usefull:This one use mosfet transistor and transformerhttp://www.homemade-circuits.com/2012/05/make-this-1kva-1000-watts-pure-sine.htmlThis is very detailed, but the filter math is difficult to undertoodhttp://www.ece.rutgers.edu/files/capstone/capstone2014/Solar-Inverter/Capstone_Design_Final_Report.pdfPlease, there is a way to use all this IRF1407, and the transform (11 + 11 to 220V) ?. They are the most expensive components.

author: lukaq
author_rank: Regular Contributor
timestamp: December 06, 2015, 05:22:13 am
content: You should really use something like:http://www.ebay.com/itm/Pure-Sine-Wave-Inverter-SPWM-Board-EGS002-EG8010-IR2110-Driver-Module-/331677342803?hash=item4d39829c53:g:O9QAAOSwo0JWF4zH

author: station240
author_rank: Unknown
timestamp: December 06, 2015, 06:00:37 am
content: Quote from: dtomazini on December 06, 2015, 12:41:58 amNot sinewave, or at least not a complete design (where's the filter ?).also 60V DC rail.Quote from: dtomazini on December 06, 2015, 12:41:58 amShould be possible, same sort of components used in 12V to 220V inverters, UPSs etc.Here is a technical explanation of how sinewave generation should work.http://electronics.stackexchange.com/questions/191742/how-is-a-pwm-signal-converted-to-sine-using-a-transformerThe basic modules that make up a sinewave inverter should be:1) sinewave generator2) PWM stage3) drive and power stage (eg your IRF1407)4) transformer5) LC filter (inductors + capacitors)The LC filter is the critical part, if the circuit doesn't have one, it's not a sinewave inverter (or at least not a complete design).The filter could also be on the other side of the transformer, which would work better I think.My advice, get the drive and output stage functioning, without overheating etc. then you just need the sinewave/PWM circuit which should be easier to find.

author: oldway
author_rank: Super Contributor
timestamp: December 06, 2015, 09:25:07 am
content: QuoteNo way, transformer is also wrong, you will get max 90Vac output in pure sine wave with this transfo...As I said, the guy who design this does not know nothing about power electronics.Perhaps you could use it to make a laboratory power supply ?

author: nowlan
author_rank: Frequent Contributor
timestamp: December 06, 2015, 12:47:49 pm
content: I was looking at pure sine wave inverters today.Do they all ramp up 12v via inductor to say 300vdc, then use push pull or pwm through a capacitor to generate a sinewave?

author: bktemp
author_rank: Super Contributor
timestamp: December 06, 2015, 12:55:10 pm
content: Quote from: nowlan on December 06, 2015, 12:47:49 pmYou can also put a pwm signal into a mains transformer and use its stray inductance with a capacitor at the output as low pass filter.

author: dtomazini
author_rank: Contributor
timestamp: December 06, 2015, 04:45:05 pm
content: Quote from: station240 on December 06, 2015, 06:00:37 amThanks station240, perhaps it's possible to do this using the sinewave/PWM board like lukaq advise:http://www.ebay.com/itm/Pure-Sine-Wave-Inverter-SPWM-Board-EGS002-EG8010-IR2110-Driver-Module-/331677342803?hash=item4d39829c53:g:O9QAAOSwo0JWF4zHThe drive and output stage could be something like this (with 12V on rails):

author: wraper
author_rank: Unknown
timestamp: December 08, 2015, 01:52:13 pm
content: Quote from: dtomazini on December 06, 2015, 04:45:05 pmSorry, but that schematic will not do any good. You could get it work but the efficiency will be less than 50% making it a huge heater rather than inverter. Moreover it won't give you stable voltage output. So you will be just wasting the money spent for the solar panels.

author: theoldwizard1
author_rank: Regular Contributor
timestamp: January 01, 2016, 04:43:15 pm
content: You all need to keep up with the technology !First a little background. To make a low voltage DC to higher voltage AC inverter takes 2 circuits.The first circuit is a PWM push-pull controller to a CT transformer. There are several chips that can do this. TL594 and UC3525 are just a couple. The transformer will likely have to be hand wound for the desired 1st stage output voltage. After rectification(use Schottky diodes because the PWM circuit is typically running 40-100kHz)and some filtering, you have a "high" voltage signal(must be >(Vp-p) * (2.0**0.5) of the desired final AC voltage)The second circuit is even EASIER ! Get an EG8010 ASIC. It will handle it all. Just add some drivers and a little more filtering and you are done. You will probably want some cheap micro to monitor voltage and temps, turn on fans, etc etc.The EG8010 is a very interesting chips. My analysis(and this is simple from studying the datasheet so I could be wrong)is there are 3 parts to this chip. First there is a crystal controlled sine wave generator. This is then feed to a Class D amplifier which controls the final drivers(typically with a "booster" in between). The 3rd part is logic that controls various function like output voltage (110/220) and frequency (50/60).These chips are quite inexpensive and available on eBay.