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pure sine wave oscillator for mosfte based inverter

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maicael

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Need one to drive my power stage with features like voltage regulation so it does not drop when loss is applied.
 

MrAl

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Hi,

Is this a single non adjustable frequency then or does it have to be adjustable?
Also what power output do you need?
 

maicael

Member
Well the frequency can be adjusted to either 50 or 60 hz and as for power output well looking to build a 1kva inverter.just need a good sine wave oscillator circuit to drive the power stage.
 

shortbus=

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Since mosfets are basically an electronic on -off switch, a simple sine wave oscillator is not much use to them. It's done by comparing a sine wave to a triangle/saw tooth wave. This is then used to drive the mosfets in a on/off pattern, similar to a PWM signal.

If the mosfets were just using a sine wave to drive the gates, they would spend too much time in the linear region. This would cause them to heat up and die, very fast.

Here is a good college thesis on inverters, and the link. http://www.google.com/url?sa=t&rct=...0Au0ipm_kcr6T4GzoW6tc1w&bvm=bv.48705608,d.aWc
 

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maicael

Member
Since mosfets are basically an electronic on -off switch, a simple sine wave oscillator is not much use to them. It's done by comparing a sine wave to a triangle/saw tooth wave. This is then used to drive the mosfets in a on/off pattern, similar to a PWM signal.

If the mosfets were just using a sine wave to drive the gates, they would spend too much time in the linear region. This would cause them to heat up and die, very fast.

Here is a good college thesis on inverters, and the link. http://www.google.com/url?sa=t&rct=...0Au0ipm_kcr6T4GzoW6tc1w&bvm=bv.48705608,d.aWc
thank you for the insight into how it works.since this is achieved by comparing with a triangle wave before driving the gates in an on/off pattern do you have a circuit that does just this.would lobe to read the pdf file attached all to the end but am so busy with other stuffs that don't really have enough time on my hands as I also work so most times I am doing my projects in the night and I still have to go to work the next morning.thanks again
 

MrAl

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Most Helpful Member
Well the frequency can be adjusted to either 50 or 60 hz and as for power output well looking to build a 1kva inverter.just need a good sine wave oscillator circuit to drive the power stage.

Hi,

Oh ok, so you are building a power inverter. That is different then. Normally when you want to build a power inverter you use a switching circuit not a linear circuit. A linear circuit (sine wave oscillator) is used as a reference signal for example, not really for powering something, except as a test tool where a pure sine wave is needed for testing something else usually for a relatively short time duration.

A power inverter requires a set of switching transistors where they are turned on and off not driven with a sine wave. So to this end you should read up on this topic more and there is a link in the previous post which seems appropriate to your end goal so i would advise reading that to become familiar with the methods often used for these kinds of projects.

It's not a simple task though and there are a few pitfalls that you might run into. You'll also want to study transistor H bridges a little too.
 

shortbus=

Well-Known Member
Most Helpful Member
thank you for the insight into how it works.since this is achieved by comparing with a triangle wave before driving the gates in an on/off pattern do you have a circuit that does just this.would lobe to read the pdf file attached all to the end but am so busy with other stuffs that don't really have enough time on my hands as I also work so most times I am doing my projects in the night and I still have to go to work the next morning.thanks again
Like MrAl said this is not a simple thing to make. It's definitely not a beginner project. And to think it can be done without research is kind of foolish. The link I gave is a very beginning to actually making one. Also like he said an understanding of H-bridges and even class "D" amplifiers is a must to make a good one.

If you think one can be made for less than the price of a purchased, proven one you will be wrong and disappointed in the end. Sorry, not trying to be mean, just truthful.
 

unclejed613

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Most Helpful Member
there was a Sony application note back in the 1970s, where they used an audio power amplifier with the output connected directly to an outlet box. the amplifier was an 1800W/ch monster, and with it running near clipping, each channel could provide a 120V sine wave at any audio frequency. running it in bridged mode, it could drive 240V loads. this probably wouldn't be a good candidate for an inverter, because the required rail voltages are +/-200V approximately. such rail voltages could, however be generated from a 12 or 24V source using a switching supply much like what you find in car-fi power amps.

there's also a way to make an amplifier self oscillate at a given frequency, which can be found here http://sound.westhost.com/project59.htm
 
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