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how to convert a square wave output from SG3524 to sine wave using op-amp or...

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EMMANUEL TOM

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Please am building a inverter project with the chip SG3524, I want to ask if there is away to convert it output wave to sine wave
 

spec

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Please am building a inverter project with the chip SG3524, I want to ask if there is away to convert it output wave to sine wave
Hi ET,

The SG3524 is a driver chip. Normally for an inverter you would also need two power switching devices (MOSFET, BJT ot IGBT) and an output transformer.

There are basically two types of sine wave inverters: pure sine wave and modified sine wave.

We need to know a lot more information than you have provided:
(1) waveform, pure or modified
(2) input source (voltage and current)
(3) output required: voltage and current
(4) frequency required

Failing that if you just want a direct answer to your question, no you cannot convert the output of an SG3524 to sine wave.

spec

PS: unless you would like to build an inverter for the fun/experience, it would be far easier/quicker/cheaper to buy an inverter.
 
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audioguru

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An inverter drains a battery so you want the inverter to very efficient and not waste battery power by making heat.
1) If you filter the output of a squarewave inverter to make a low frequency sinewave then the filter parts will be huge and expensive and they will waste a lot of battery power making heat. Also the output voltage will be low.
2) If you filter the low frequency squarewave output of an SG3524 IC to make a low frequency sinewave then you can use a powerful linear audio amplifier to make a powerful sinewave and waste a lot of battery power making heat.
3) Use #2 above but use an efficient class-D audio amplifier.
4) Use a Pulse-Width-Modulation system (PWM) using a high frequency squarewave that works like a class-D amplifier and its output is a low frequency sinewave with hardly any wasted power making heat..
 

spec

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An inverter drains a battery so you want the inverter to very efficient and not waste battery power by making heat.
1) If you filter the output of a squarewave inverter to make a low frequency sinewave then the filter parts will be huge and expensive and they will waste a lot of battery power making heat. Also the output voltage will be low.
2) If you filter the low frequency squarewave output of an SG3524 IC to make a low frequency sinewave then you can use a powerful linear audio amplifier to make a powerful sinewave and waste a lot of battery power making heat.
3) Use #2 above but use an efficient class-D audio amplifier.
4) Use a Pulse-Width-Modulation system (PWM) using a high frequency squarewave that works like a class-D amplifier and its output is a low frequency sinewave with hardly any wasted power making heat..
Hi AG,

A bit of education for me: it is something I have never been clear about and it is along the lines that you mentioned.

Say you had a fundamental switching frequency of around 100Khz giving many pulses in a half sine wave of the 50Hz/60Hz inverter transformer input. Can you modulate the pulse widths to simulate a sine wave in the primary of the output transformer without the need of a high frequency transformer. My thought is that a 50Hz/60Hz transformer would simply integrate out the 100KHz pulses- perhaps that is what you are effectively suggesting- or is there more to it than that.

spec
 
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crutschow

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Perhaps you can configure the SG3524 to input a sinewave of the desired frequency, (I assume 50 or 60Hz), such as from a phase-shift sine-wave oscillator, to the IN+ or IN- inputs to generate a PMW sinewave modulated output.
This output can be LC filtered or run through a transformer to give a power sinewave output at the oscillator frequency.
Here's a circuit that attempts to do that but it apparently has some problems with the output circuit.
 

audioguru

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A low frequency transformer will not pass the kHz PWM frequencies. A low frequency transformer is large, heavy and expensive (and it works poorly). A high frequency transformer is small, light weight and cheap (and it works well).
 

spec

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A low frequency transformer will not pass the kHz PWM frequencies. A low frequency transformer is large, heavy and expensive (and it works poorly). A high frequency transformer is small, light weight and cheap (and it works well).
Ah, yes I understand that well, but can you use a small high frequency transformer by chopping up the half sine wave, say with 100KHz. For the duration of the half sine wave the flux will all be in the same direction so won't you need a large cross section core to stop the transformer from saturating?

spec
 

EMMANUEL TOM

New Member
Hi ET,

The SG3524 is a driver chip. Normally for an inverter you would also need two power switching devices (MOSFET, BJT ot IGBT) and an output transformer.

There are basically two types of sine wave inverters: pure sine wave and modified sine wave.

We need to know a lot more information than you have provided:
(1) waveform, pure or modified
(2) input source (voltage and current)
(3) output required: voltage and current
(4) frequency required

Failing that if you just want a direct answer to your question, no you cannot convert the output of an SG3524 to sine wave.


Hi spec thanks,
(1) any of the two but since the pure sine wave will not be easier, I prefer the modify sine wave
(2) yeah
(3)yeah
 

spec

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Hi ET,

Got the sine wave bit but you have not answered questions (2), (3), and (4).

spec
 

crutschow

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A low frequency transformer will not pass the kHz PWM frequencies. A low frequency transformer is large, heavy and expensive (and it works poorly). A high frequency transformer is small, light weight and cheap (and it works well).
But to demodulate the PWM signal and generate the low frequency modulation (50 or 60Hz) for he inverter output you will need a large mains type transformer that passes the low frequency and rolls off he high frequency.
It needs to act as a low-pass filter.
 

audioguru

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Class-D audio amplifiers use PWM and do not get hot, operate the switching at hundreds of kHz, produce output frequencies down to 10Hz and do not have an output transformer. Some do not even have a lowpass filter at the output but when they do it is small and cheap. An inverter can be the same.
 

spec

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Class-D audio amplifiers use PWM and do not get hot, operate the switching at hundreds of kHz, produce output frequencies down to 10Hz and do not have an output transformer. Some do not even have a lowpass filter at the output but when they do it is small and cheap. An inverter can be the same.
Yes, agree that the amplifier dissipation will be very low but, that does not address the question about the flux in the primary of the output transformer. I simply do not know the answer.

spec
 

crutschow

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Class-D audio amplifiers use PWM and do not get hot, operate the switching at hundreds of kHz, produce output frequencies down to 10Hz and do not have an output transformer. Some do not even have a lowpass filter at the output but when they do it is small and cheap. An inverter can be the same.
Only if you don't need to increase the output voltage from the PWM signal.
 

spec

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Hi all,

I have worked out the situation with the output transformer in an inverter. The situation is not the same as in a switched mode power supply where the inductor size can be reduced by increasing the switching frequency.

While pulse width modulation minimizes the dissipation in the transformer driver, PWM does not limit the flux in the output transformer. To the transformer it makes no difference if the input sine wave is continuous or chopped- the net flux in one direction, during one half of an input sine wave, is exactly the same, by definition.

I wondered why there is always a large mains type transformer in inverters.:)

spec
 

Les Jones

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Hi spec,
Some more modern inverters use a high frequency inverter to generate about +/- 300 volts DC and just chop that into a rectangular wave form. I do not see why the swiching of the high voltage DC could not be pulse width modulated to produce something close to a sine wave.

Les.
 

spec

Well-Known Member
Most Helpful Member
Hi spec,
Some more modern inverters use a high frequency inverter to generate about +/- 300 volts DC and just chop that into a rectangular wave form. I do not see why the swiching of the high voltage DC could not be pulse width modulated to produce something close to a sine wave.

Les.
Thanks for the information Les- that sounds like a pretty clever approach.

No, there is no reason why the output sine wave should not be pretty good with a touch of filtering.:)

spec

PS: off topic, but have you come across a unit that will input 12V DC and produce around 400V DC at about 200mA. The output does not need to be isolated or even stabilized.

I know you can make one pretty easily, but I would like to buy a ready made unit, preferably a single board
 

tcmtech

Banned
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Hi spec,
Some more modern inverters use a high frequency inverter to generate about +/- 300 volts DC and just chop that into a rectangular wave form. I do not see why the swiching of the high voltage DC could not be pulse width modulated to produce something close to a sine wave.

Les.
That concept has been around for 30+ years now and is standard industry design in most very portable power inverter. Most typically don't use a +- HV secondary though. Simple single rail 150 - 170 VDC, for our American 115 - 120 VAC output units, with a bare bones basic H bridge for the reconversion to the square wave output.

They're also pretty easy to hack into their HV DC side rail voltage feedback loop and H-bridge driver circuit to get variable voltage and variable frequency operation as well. That and refitting one of those cheap SPWM driver boards into a larger power inverter to convert it to sine wave output is not that hard either.

As for the older iron core transformer based units they are easy to make into sine wave inverters as well with those circuit boards I linked to. Just replace the original driver board with one of those and that's it.
I have a bout 20 old 1000 - 3000 watt Trace power inverters I picked up over the years that I want to do that conversion to to make them into decent usable units. Their over priced and overly complex driver boards went out and aren't worth the cost and hassle to repair so I figured they would be good units to redesign some day.
 

audioguru

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I was also thinking of the small, lightweight and ferrite cored transformer stepping up the low voltage high frequency, then the high frequency high voltage that is produced is rectified and used to power the high frequency PWM modulated Mosfets.
 
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