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Are datasheets important?


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Our Low Cost 500W Inverter project uses a CD4047 oscillator IC which divides the oscillator frequency by 2 for a 50Hz output from the inverter.

The project originally used a 100 ohm resistor and a 4.7uf capacitor for its 100Hz oscillator. Somebody (a God) changed the resistor's value to 1k.

Is this correct? No.
In the datasheet, Texas Instruments says the minimum resistor value is 10k, then the frequency formula is 1 divided by 2.2 times RC.

The original 100 ohms with 4.7uF (where can you buy an inexpensive 5% 4.7uF capacitor that is non-polar?) calculates to have a frequency of 967Hz. It is not anywhere near 100Hz. Why?

The INTERNAL RESISTANCE of the inverters in the IC makes the formula incorrect when a low value resistor is used:
1) 100 ohms with 4.7uF= 96.7Hz if the 900 ohm internal resistance is included in the formula.
2) 1k ohms with 4.7uF= 50.9Hz if the 900 ohm internal resistance is included in the formula.
3) 47k ohms with 100nF= 94.9Hz if the 900 ohm internal resistance is included in the formula.

I use the 47k resistor with an inexpensive 100nF 5% capacitor in my version of the oscillator.
Our project with a 1k resistor and a 4.7uF capacitor is wrong.

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Watch it AG, you might get deleted! ;D ;D

I think I got banned at least one time, then I changed my IP address and got back in. ;D

It is too bad that the thread with a detailed discussion about the 500W inverter's problems got deleted.
Did you notice that it uses two quad opamps instead of a single dual opamp?


MP,
Please make the oscillator correctly, according to the datasheet.
Use a correct value for the resistor and don't use a capacitor that is 100 times too big.
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Sorry, no can do.
I have no intentions of redesigning the projects on this site. Don't waste my time.
Besides, there are those who have built this project and report it to be working well. That has quite a bit of weight over your claims since you have not built it.

MP

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there are those who have built this project and report it to be working well. That has quite a bit of weight over your claims since you have not built it.
MP


Nobody has posted in a forum here that the original faulty "500W" inverter project works.

This forum is for discussing THEORY.
This topic discusses the wrong way its oscillator parts were chosen.
Texas Instruments recommends a resistor with a minimum value of 10k ohms in their datasheet for the CD4047 oscillator. The author of this project used only 100 ohms because his capacitor was much too big.

The original project was full of short circuits that I fixed and it didn't and still doesn't have enough output transistors for anything more than only 250W or 300W.
It doesn't have any protection from voltage spikes from its transformer and from an inductive load.
It uses TWO quad opamps instead of a single dual opamp.

I don't need to make a faulty project to find out it is wrong, I just look at its schematic.
I have made many Cmos oscillators like this one correctly.

Datasheets have max ratings and recommended parts values that should be followed.
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Since this topic is about the importance of data sheets, I will add a little to that.

Data sheets are very important to get an image of what a product can do and where it has limitations. The data sheets will give you some test results as examples, but one should note these tests are not the full story. They are only an example to get you started. If you limit yourself to the specs of the tests performed for the data sheet, you will have a workable design. However, if you perform additional testing of the device, in most cases, you will find that there are many more capabilities. This is where the split between theorist, hobbyist and R&D Engineer becomes clear. Only designing to the specs written in a data sheet are correct, and it will work well. However, performing tests and designing to parameters not given or specified in a data sheet are also correct as long as the testing was performed correctly to insure it is not a one-time result. This can work both for you and against you. There are other things such as elevation, barometric pressure, relative humidity, solar radiation,etc that sometimes must be addressed even though the spec sheet does not give you specification regarding it.
Designing only from a spec sheet, will give you a workable product, but certainly leaves one with limitations compared to a design that is tweaked on the bench.

MP

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The author of the "500W" inverter project selected a 4.7uF capacitor for the oscillator at random.
R&D engineers calulate parts values properly. I selected 100nF by calculating it properly, and knowing that a nonpolar and an accurate 5% one is inexpensive. My calculated 47k resistor makes the oscillator correct for a 50Hz output and 39k makes a 60hz output. Will changing the resistor in the author's circuit give a 60Hz output?

Then the author bench tested the oscillator and found that a resistor value of only 100 ohms made its frequency correct. He tested only one. He didn't know that the internal resistance of the IC was a major part of the total resistance and didn't know that different ICs would produce vastly different frequencies.

The author didn't know about the minimum recommended resistor value of 10k for the calculation to to be correct.
Maybe he didn't know that the capacitor must be non-polar.
Maybe he tried a powerful 555 oscillator first, then used its low value resistor and polarized electrolytic capacitor with the low power CD4047 oscillator by mistake.

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Perhaps the oscillator works with the 100R resistor? but other data for the circuit might not live up to the datasheet values with this higher load! As an example the temperature range promised in the sheet might not be fulfilled! Also I suspect that stability will be affected with this extra load. Sure you can go outside some of the parameters but not without influencing another. I have (by mistake) run a 555 on 24VDC and it got very hot but it survived even though the datasheet says 18VDC!
I know that a light bulb (which in its datasheet is) designed for 12V will work fine at 18 V, however I don

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Perhaps the oscillator works with the 100R resistor? but other data for the circuit might not live up to the datasheet values with this higher load!

It might be very intermittent with a load current 100 times its recommended maximum. Yesterday it worked. Today it didn't work and blew its fuse. Tomorrow it might work or it might not work.
The CD4047 IC  has an internal resistance that is hundreds of ohms so the oscillator might work without a resistor, but its frequency would be different for each different IC.
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The author of the "500W" inverter project selected a 4.7uF capacitor for the oscillator at random.
R&D engineers calulate parts values properly.


It is my understanding that the author of the project is an R&D Engineer. I have seen him elsewhere on the web. You are throwing out rumor and speculation instead of fact. (theory?  ;D ) Are you claiming to be an R&D Engineer? You stated what R&D Engineers do, then you started talking about your selection. I was a little confused of the meaning behind that.

MP
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Hi




It is my understanding that the author of the project is an R&D Engineer. I have seen him elsewhere on the web. You are throwing out rumor and speculation instead of fact. (theory?  ;D ) Are you claiming to be an R&D Engineer? You stated what R&D Engineers do, then you started talking about your selection. I was a little confused of the meaning behind that.

MP



I believe that Mr. [glow=red,2,300]AUDIOGURU[/glow] is a big  R&D Engineer, and he is the best one i meet in a forum
OK i'm not so good in electronics, but I can distinguish between person and person, and I know from the answer the person's abilities.
Therefore, I ask everyone to deal with Mr. AUDIOGURU courtesy and respect because he deserves it 
thanks
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I saw the author's photograph in Google. He looks "unusual".
He is a research engineer for satellite communications at a university in Singapore.

He made many mistakes with this inverter project:
1) The wiring for the CD4047 IC shorted the power supply.
2) The CD4047 had the wrong value resistor and capacitor.
3) The 2N3055 transistors were wired wrong.
4) There are only four 2N3055 output transistors for 250W output instead of eight transistors for 500W output.
5) There are two quad opamps instead of a single dual opamp.
6) No fuse.
7) The circuit has no protection diode to stop inductive voltage spikes.

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Walid,
Perhaps you have misunderstood the conversation. No one has been disrespectful to audioguru. However, you might not know that audioguru is not an R&D Engineer. In fact, he is not an Engineer. He mentioned in another forum that he did not complete his Engineering course.
In regards to being disrespectful, I find it disrespectful to say someone looks unusual when discussing their knowledge or capabilities. It is an insulting statement. Ones appearance has nothing to do with ones Electronic knowledge or capability.

MP

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I can't help it, I just have to get into it at this point.

An Engineer is a qualification as shown on paper, but an engineer is a way of thinking.  I am not the first (yet).

From what I have seen, Audioguru has shown aspects of the second from time to time (like me).

"Looks unusual"?  Please qualify this, Audioguru.  It will sound too close to prejudice to the uninformed masses (like me) if this statement stands alone.

Yes I agree that datasheets are important, and compliance with them is wise.  There is another thread that seems to advocate something that is not strictly in the datasheet of a certain device, which may have your influence.  I do believe that some logical reasons were outlined, which has the earmark of an engineer.

As for the article- I haven't looked at it directly.  What I've read of it here does lead me to believe that- the author was having a bad day, or it was written early in his career, or there were tradeoffs that may have resembled a marketing influence (500W is absolute, one time only, run for your life maximum rating- don't ever count on it) like my 13,000,000W stereo (fictitious device).

As for the article (still haven't read it), it may be wise to append that someone who may be qualified to speak on the subject (which I believe he is) is not comfortable with the specifications as given and recommends some alterations- but the original project is not yet known to fail.

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First I used the dictionary for translation so please forgive that there were some errors in language

In fact, he is not an Engineer


OK, I'm engineer in communication and control, 5 years in university after high school , Despite this, I feel myself as if I'm small and stupid pupil when discuss [glow=red,2,300]GURU[/glow].
I know many of Engineers, and dealt with through the hundreds of forums, and even in this forum did not find a better than [glow=red,2,300]GURU[/glow].
Obtaining a degree in engineering is required, but not enough. The world needs a genius like [glow=red,2,300]GURU[/glow], does not need papers written in it a certificate in engineering.
Why take advantage of the engineer does not understand anything and does not have something to offer to society.

For all these reasons, I find that even [glow=red,2,300]GURU[/glow] right to criticize any person manner it/he deems appropriate
when [glow=red,2,300]GURU[/glow] says that, I believe this because [glow=red,2,300]GURU[/glow] said that.
Do not think I crazy or naive, in the community that I live in, we have a saying heritage states : [glow=red,2,300]"Who taught me a characters I was a slave to him " [/glow]
Only [glow=red,2,300]GURU[/glow] taught me milions of characters and was patient on my often mindless questions.   
In the end, I say to all that [glow=red,2,300]GURU[/glow] precious wealth of scientific I hope to preserve and benefit from him

Ask God to extend his life And live happily with his family.
thank you [glow=red,2,300]GURU[/glow]
thank you MP
Thanks to all Forum members 
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I did so complete my engineering course. I have my degree.
I did not have a mentor so I could not complete the internship required for me to be registered as a professional engineer in Canada. I was too busy designing circuits and improving existing ones.

In my carreer I performed the job of an engineer but I could not call myself an engineer.

I am sorry I said that the author of the 500W inverter "looks unusual". I have never been to his planet and I have never been in a mosque where probably everyone there looks like him.
You can see for yourself if he looks like people you know.

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Wow...has this gotten off course to the topic.
In response to that ...not completing the part of the course which required a mentor is what I was referring to. The course is not complete. As your school would advise, the mentoring is an important part of the coursework to become an Engineer. This is recognized by Canada as a necessity. Otherwise it would not be required in order to register as an Engineer. Perhaps I could have simply stated to Walid that AG is not a registered R&D Engineer in Canada where he lives. My main point in posting was that AG stated the original author was not an R&D Engineer and he was.
Rebutting that statement with comment that the author looks strange and posting his picture as such speaks of prejudice and bigotry such as I have seen in other posts from AG. Many of which I have deleted in hopes that no one would see them before hand. This is an International forum. No one on this community has a right to put down anyone else based on where they live, what they look like, their ethnic background, or religious beliefs, etc. We all live in this world and all of us here on this forum are members because we have a common interest. Let's keep the other garbage out of it.

As a final note I would like to say that this is not supposed to be a discussion of anyone's aptitude or appearance, although it did turn into that direction with Walid's conversation about respect. Please continue discussing the importance of data sheets here. There are other places on this community where you can talk about anything that you so desire (provided it is in line with the rules of the forum). Please help keep the community organized in their categories.

Thanks,

MP

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As I stated before, I use data sheets as a guideline only. I have saved companies loads of money by designing and redesigning products to use lower grade components. The important part is to understand what parameters may be exceeded under which conditions and to design around the limitations.

The one thing that separates the Technician from the Engineer is the ability to design and evaluate using advanced circuit analysis and mathematics which goes beyond just

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Hi AN920,
If you were designing this 500W inverter, would you use a huge, expensive and poor tolerance non-polar 4.7uF capacitor with a 100 ohm resistor in its CD4047 oscillator, when the manufacturer of the CD4047 recommends using a minimum of 10k for the resistor?
Each IC would make a very different frequency due to the variable on-resistance being much higher than the resistor's value.
Wouldn't a smaller, less costly and good tolerance 100nF capacitor with a 47k resistor be much better?

Would you cut in half the required number of output transistors so that they operate at double their absolute max current rating?

Would you use two quad opamps instead of a smaller and less expensive dual opamp?

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I would not use bipolar power transistors in a push-pull configuration period! (many hidden problems to the inexperienced, especially at high current levels)

I would not use 50/60 Hz inverter transformers. (too bulky)

The 4047 would be last on my list of choices. (hate RC timing constants, prefer XTAL)

It would we a different design all together. (HF switching)

I would use opamps only for feedback, protection and regulation functions and not for
drivers.

I am saying this based on my experience of designing a commercial 5kW UPS for one of my previous employers.

I designed some 400Hz inverters for aviation applications in the 70's using bipolars but using proper precautions like using clever base drive circuitry, baker clamps, device desaturation detection, transformer saturation detection etc. Today most things are much easier and safer using power mosfets and dedicated drivers.

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I will say this in a Q & A session:-

Are there questionable design practices involved?
Yes, whether we like it or not. This is just not the way things are done by power electronic designers. This may be due to the fact that this is not the area of expertise of the creator of this design.

Does this flame the designer?
No, he may be brilliant in other areas.
I can write software that works but I suck compared to some other people I know.

Will it work?
Maybe under low power conditions for short periods.

Will it work reliably under the claimed power for extended periods?
Probably not.

Can it be improved?
Like everthing, yes. Here the best way will be to contact the designer and point out any potential problems and work with him towards a solution. Engineers in general are humble people and should not feel offended by this action. Most will welcome any advice to improve a design.








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