50 Hz oscillator based on a LM324N IC

[iods]

its a "Grid tied inverter" isnt it?

a grid tie inverter would be too big , too powerful , that's for solar panels and wind turbines , I'm only looking for a 500 W DC to AC inverter ,

 

[iods]

I made this circuit in LTSPICE , I think it outputs a 200 Hz square wave , tell me what do you guys think

file is in the attachments

 

[AnalogKid]

the output voltage of the LM324 doesn't really matter because the MOSFETs are voltage based and can be driven by a very low voltage.

Not exactly. They can be driven by a very low current, but need much more voltage than a bipolar transistor. A power MOSFET usually requires at least 10 V Vgs for full enhancement (minimum Rds). Logic-level parts require less, but usually have higher Rdson for equivalent parameters (circuit voltage, drain current, cost, etc.)

ak

 

[alec_t]

I think it outputs a 200 Hz square wave

218Hz. Near enough .

 

[iods]

218Hz. Near enough .

I edited that to 50 Hz , can I now drive the mosfests and the Transformer to get a 220v at 50Hz ?

 

[Les Jones]

You need to post a shematic of exactly how you plan to drive the mosfets from the oscillator before we can answer that question. Even in old fashioned inverters it was not normal to drive the switching elements with a simple square wave. There would be a period of time when neither mosfet was switched on. This is to make the waveform nearer to a sine wave. Even this does not work with some equipment such as induction motors. Modern inverters step up the input voltage first using a high frequency inverter to about plus and minus 300 volts DC then do the 50 Hz switching. This reduces the weight and cost of the transformer.

Les.

 

[audioguru]

What do you have that can be powered from a 50Hz squarewave? A heater or an incandescent light bulb? Electronic products usually rely on the higher peak voltage of a sinewave.

 

[iods]

You need to post a shematic of exactly how you plan to drive the mosfets from the oscillator before we can answer that question. Even in old fashioned inverters it was not normal to drive the switching elements with a simple square wave. There would be a period of time when neither mosfet was switched on. This is to make the waveform nearer to a sine wave. Even this does not work with some equipment such as induction motors. Modern inverters step up the input voltage first using a high frequency inverter to about plus and minus 300 volts DC then do the 50 Hz switching. This reduces the weight and cost of the transformer.

Les.

I know induction motors and so on won't work on a square wave this is only to light up a bulb , a heater , stuff like that

but what do you mean a high frequency inverter ? I understand what stepping the voltage up is but plus and minus ? tell me more about it

 

[iods]

What do you have that can be powered from a 50Hz squarewave? A heater or an incandescent light bulb? Electronic products usually rely on the higher peak voltage of a sinewave.

I can convert the square wave into a sine wave no ?

 

[audioguru]

A sinewave inverter does not amplify a 50Hz sinewave or use a transformer to stepup the voltage of a 50Hz sinewave because a 50Hz transformer is huge and for a 500W output the transistors will heat with about 400W. Instead Pulse-Width-Modulation (PWM) is used to modulate a high frequency squarewave with a 50Hz sinewave so that the high frequency transformer is small and the switching transistors do not get hot.

 

[iods]

A sinewave inverter does not amplify a 50Hz sinewave or use a transformer to stepup the voltage of a 50Hz sinewave because a 50Hz transformer is huge and for a 500W output the transistors will heat with about 400W. Instead Pulse-Width-Modulation (PWM) is used to modulate a high frequency squarewave with a 50Hz sinewave so that the high frequency transformer is small and the switching transistors do not get hot.

well I do have a huge transformer , but anyway , I'm not so familiar with PWM inverters , gotta read more abt that

 

[spec]

Hi iods,

Below is an outline schematic of a square wave inverter to give you an idea of what would be involved.

spec

​

NOTES
(1) The above inverter would produce a square wave as opposed to a sine wave.
(2) The output would be a 220V peak square-wave (the same RMS value as a 220V RMS sine wave)
(3) The NMOSFET types are not shown. There is a wide range of NMOSFETs but some pretty hefty types would be required for a 500W RMS output. With a 500W load the current taken from the battery would be around 50 Amps.
(4) The NMOSFETs would require substantial heatsinks
(5) The NMOSFET driver chip does not provide dead-time. Dead-time would be advisable in practice. Dead-time is where there is a delay between one NMOSFET turning off and the other NMOSFET turning on. This avoids the situation where both NMOSFETS are conducting together, which is very undesirable, both for the NMOSFETs and the transformer.
(6) Capacitors are disc ceramic with an X7R dialectic.
(7) An LM324 operational amplifier would not be the best choice for a 50Hz oscillator. An LM393 comparator would be better but, an LM555 timer would be better still (the circuit would require modification to use a standard LM555 timer). And an LMC555 CMOS version- as shown- would be better again. But, if you really want to use an LM324 oscillator, just say and I will post a schematic for a suitable circuit to replace the LMC555.
(8) It would be possible to generate a precise, highly stable, 50 Hz frequency by replacing the timer chip with a crystal-controlled 50Hz generator. But that would be more complicated.
(9) The NMOSFET driver chip is necessary to drive the highly capacitive NMOSFET gates with high currents so that the NMOSFET turn on and off fast.
(10) The resistors in the gates of the NMOSFETs are for shaping the waveform at the NMOSFET gates.
(11) Snubbers, which would probably be required on the NMOSFET drains, are not shown.

 

[iods]

Hi iods,

Below is an outline schematic of a square wave inverter to give you an idea of what would be involved.

spec

View attachment 103365
​

NOTES
(1) The above inverter would produce a square wave as opposed to a sine wave.
(2) The output would be a 220V peak square-wave (the same RMS value as a 220V RMS sine wave)
(3) The NMOSFET types are not shown. There is a wide range of NMOSFETs but some pretty hefty types would be required for a 500W RMS output. With a 500W load the current taken from the battery would be around 50 Amps.
(4) The NMOSFETs would require substantial heatsinks
(5) The NMOSFET driver chip does not provide dead-time. Dead-time would be advisable in practice. Dead-time is where there is a delay between one NMOSFET turning off and the other NMOSFET turning on. This avoids the situation where both NMOSFETS are conducting together, which is very undesirable, both for the NMOSFETs and the transformer.
(6) Capacitors are disc ceramic with an X7R dialectic.
(7) An LM324 operational amplifier would not be the best choice for a 50Hz oscillator. An LM393 comparator would be better but, an LM555 timer would be better still (the circuit would require modification to use a standard LM555 timer). And an LMC555 CMOS version- as shown- would be better again. But, if you really want to use an LM324 oscillator, just say and I will post a schematic for a suitable circuit to replace the LMC555.
(8) It would be possible to generate a precise, highly stable, 50 Hz frequency by replacing the timer chip with a crystal-controlled 50Hz generator. But that would be more complicated.
(9) The NMOSFET driver chip is necessary to drive the highly capacitive NMOSFET gates with high currents so that the NMOSFET turn on and off fast.
(10) The resistors in the gates of the NMOSFETs are for shaping the waveform at the NMOSFET gates.
(11) Snubbers, which would probably be required on the NMOSFET drains, are not shown.

thanks a lot spec , and yea , I gotta use the LM324 because it's what I have , here where I'm from i couldn't find any of the 555 timers or the LM393 , unless i can scavenge it from some old electronic board , but I dunno where to look

 

[spec]

thanks a lot spec , and yea , I gotta use the LM324 because it's what I have , here where I'm from i couldn't find any of the 555 timers or the LM393 , unless i can scavenge it from some old electronic board , but I dunno where to look

OK iods,

I will just post an LM324 50Hz oscillator as that is what you want.

Just let me say that you will need some more components to build a 500W inverter, but perhaps you plan on crossing that bridge when you come to it.

spec

 

[spec]

Hi iods,

Below is the schematic for an LM358 50Hz oscillator. The circuit shows an LM358 rather than an LM324 as promised in post #34 above (my error), but the individual operational amplifiers are identical. The LM358 contains two opamps, while the LM324 contains four identical opamps. You just have three spare opamps with an LM324, rather than one spare opamp with the LM358. Of course, the pin numbers will be different (check data sheet links below).

spec

​

DATA SHEET
(1) LM358: https://www.ti.com/lit/ds/symlink/lm358.pdf
(2) LM324: https://www.ti.com/lit/ds/symlink/lm2902-n.pdf

 

[audioguru]

There was a website of a Japanese guy who designed a simple squarewave inverter and he posted 'scope photos showing its horrible lack of output voltage regulation because it had no feedback. I cannot find his website now. Japan's electricity is 100V RMS and his inverter's average output was about 140V with no load and dropped to 70V with its rated load.

 

[iods]

OK iods,

I will just post an LM324 50Hz oscillator as that is what you want.

Just let me say that you will need some more components to build a 500W inverter, but perhaps you plan on crossing that bridge when you come to it.

spec

exactly yea ,
thanks a lot pal , u were a life saver

 

[iods]

Hi iods,

Below is the schematic for an LM358 50Hz oscillator. The circuit shows an LM358 rather than an LM324 as promised in post #34 above (my error), but the individual operational amplifiers are identical. The LM358 contains two opamps, while the LM324 contains four identical opamps. You just have three spare opamps with an LM324, rather than one spare opamp with the LM358. Of course, the pin numbers will be different (check data sheet links below).

spec

View attachment 103389
​

DATA SHEET
(1) LM358: https://www.ti.com/lit/ds/symlink/lm358.pdf
(2) LM324: https://www.ti.com/lit/ds/symlink/lm2902-n.pdf

In the schematics it shows that they wire the inverse input to the output of a second amp , do I have to do that to all the other amps as long as I'm using the LM324 ??

 

[cowboybob]

In the schematics it shows that they wire the inverse input to the output of a second amp , do I have to do that to all the other amps as long as I'm using the LM324 ??

Since all the OpAmps are powered simultaneously in the LM324, it's just good practice to wire them, as spec noted, to prevent any "squirrely" (i.e., unexpected) activity.

 

[spec]

exactly yea ,
thanks a lot pal , u were a life saver

No probs iods.

spec