Author Topic: Inverter schematic  (Read 6797 times)

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RobT

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Inverter schematic
« on: July 08, 2004, 07:00:16 AM »
Thanks for the prompt responses!  Hopefully I'll do this right and we'll have a pic.

This is for the controller part, not the driver output section. The info I got with the plan was convoluted to say the least, so I had to decipher what the values etc were. I'm a reasonable mimic, but don't have the knowhow to see why some things are used.

The blurb says: "The SG3525 outputs go to the 4082. It also goes to a 4017 decade counter which counts 10 pulses via resistors to form the stepwave.(This part works!)

The 1st pulse also goes to the 4013 which switches every 10 pulses, the two outputs going to the 4082 inputs. The result is 18 pulses,360 degrees of sinewave. (this I can't get to work!) The stepped waveform from the 4017 goes to the SG 3525 input, regulating the pulsewidth." (This works!) The 3140 OPAMP is used as a voltage reference, to control the AC voltage.  I redrew the schematic as the original was a waste of time. I've added a note for the usage of each variable pot, as well as the values of all components.

I hope this is comprehensive enough!  If not, I can send anything else you may need.

Thanks!



« Last Edit: July 08, 2004, 07:00:16 AM by (unknown) »

TomW

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Re: Inverter schematic
« Reply #1 on: July 08, 2004, 07:15:27 AM »
RobT;


Sorry, Windows proprietary .doc files will not display like a picture, however, folks can use "view image" in their browser to download it for viewing. At least those  who actually still use Windows. The rest of us can't view it.


Cheers.


TomW

« Last Edit: July 08, 2004, 07:15:27 AM by (unknown) »

RatOmeter

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Re: Inverter schematic
« Reply #2 on: July 08, 2004, 07:17:23 AM »
Hi,


Since there are folks here who might find it an inconvenience to open an MS Word document, I've posted the image here as a GIF file:




« Last Edit: July 08, 2004, 07:17:23 AM by (unknown) »

Ungrounded Lightning Rod

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Re: Inverter schematic
« Reply #3 on: July 08, 2004, 11:55:22 AM »
The output circuit is missing but I'll try to interpret the rest.


The bottom row is your basic sine-wave generator.  The 4017 in the lower-left corner is a ten-step decoded counter.  The ten resistors on its output form a D-to-A converter specialized to produce a ten-step approximation of half a sine wave from the moving 1.  (Note that the schematic has an error:  R17 should be 27k, not 47k, to be consistent with the rest of the circuit.)  The 4013 on the right counts which half of the sine wave you're on, so you get a twenty-step sine wave.  Q1 is an emitter-follower amplifier, to "harden up" the output voltage by sourcing more current, so the following stages don't load it down and/or distort it.


The top row is a voltage level monitor, monitoring the AC voltage and adjusting the drive to regulate it to the correct level.  The right-hand side is a "power supply", generating a DC voltage in proportion to the AC voltage.  The section with the zener provides a reference voltage, and the 3140 op-amp is a subtractor, resulting in an error voltage at the junction between diodes D2 and D2.


I THINK what's happening with D3 is that it's acting as a variable load on the sine wave from the lower row, adjusting the level of the half-sine-wave on the vertical wire on the left.  If that's right, D2 might be there to "tell" the op-amp what the shape of D3's response is.  I'd have to think about that a bit more to get it right, though.


The middle row is the basic oscilator and pulse former.  The SG3525 is a pulse-width modulator, which sets the frequency and creates a train of variable width pulses going right.  (I don't have a pinout diagram for it so I can't give you the details story.)  The pulses feed down to the 4017, advancing it one step with each pulse, and the lower row controls the pulse width.  The variable width pulses go to the 4082A dual and gate, where they are anded by the "which half-cycle" signal from the 4013.


The result is twenty variable-width drive pulses per cycle, ten on Drv-1 and ten on Drv-2.  The width of the pulses is adjusted to produce an approximation of a regulated sine wave (plus a bunch of energy at the 20th harmonic and multiples of it, which for 60 Hz would start at 1,200 Hz.)


If you have an output circuit composed of:

 - Two switching transistors

 - Two free-wheeling diodes

 - A transformer, and

 - A radio interference filter

you should get a darned good sine wave out of it.


You might also be able to substitute a couple inductors and a couple capacitors for the transformer, switching-regulator style, although 1.2 kilohertz seems a bit low for that.

« Last Edit: July 08, 2004, 11:55:22 AM by (unknown) »

veewee77

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Re: Inverter schematic
« Reply #4 on: July 08, 2004, 10:16:58 PM »
Save it to your home directory (or desktop) and open it with OOo. . .

« Last Edit: July 08, 2004, 10:16:58 PM by (unknown) »

RatOmeter

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Re: Inverter schematic
« Reply #5 on: July 12, 2004, 07:44:56 AM »
Thanks for the description.  I had guessed right on the "DAC" circuit but was confused by the resistor value error.  I should have stuck with my gut feel on that one.


Interesting thing about it is that, with today's tech, the control circuit could be vastly simplified by use of a microcontroller (with or without built-in DAC).  With just a 8 bit DAC the sine resolution could be upped quite a bit.  If the micro didn't have a DAC built in, the same resistor network trick could be done with an 8 bit output port.

« Last Edit: July 12, 2004, 07:44:56 AM by (unknown) »

Ungrounded Lightning Rod

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Re: Inverter schematic
« Reply #6 on: July 13, 2004, 06:09:35 AM »
Interesting thing about it is that, with today's tech, the control circuit could be vastly simplified by use of a microcontroller (with or without built-in DAC).  With just a 8 bit DAC the sine resolution could be upped quite a bit.  If the micro didn't have a DAC built in, the same resistor network trick could be done with an 8 bit output port.


Or (since the final output is pulse-width modulated drive pulses), with just two output lines.


But a software hang might leave an output transistor turned on.  That would saturate your output inductor in milliseconds.  If the transistor is bipolar (maybe even if it's a FET) the resulting current spike could fry it before a fuse blows).


And in the absense of explicit analog circuitry for the regulator, your voltage regulation would also be dependent on an A-to-D converter of the microcontroller, rather than a continuous adjustment.  This (along with digital generation of the pulses) would make your regulation have discrete steps.  Line surges would also be applied to the microcontroller, which may be more sensitive to them than the analog circuitry (leading to software hangs and fried output circuits...)  So you'd need protection circuitry...


By the time you're done, a microcontroller might have as much glue circuitry as this entire device.


(Then again, maybe it's just that the designers were hardware hackers rather than software types.  B-)  )

« Last Edit: July 13, 2004, 06:09:35 AM by (unknown) »

Nando

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Re: Inverter schematic
« Reply #7 on: July 13, 2004, 10:18:55 AM »
RbT:


If you send the schematic to me, I will analyze it ,


Power conversion is my trade and right now I am working one for 400 HZ generation.


Send Schematic to nando37-at-comcast-dot-net


Regards


Nando

« Last Edit: July 13, 2004, 10:18:55 AM by (unknown) »

baggo

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Re: Inverter schematic
« Reply #8 on: July 15, 2004, 03:27:45 PM »
Hi RobT,

Have just built that control circuit of yours on a breadboard and it seems to do what it should. The output from the drive 1 and drive 2 on the 4082 are a 10 step pulse train with the pulse width varying to suit the corresponding position in the 'sinewave'.

The output from drive one is out of sync with drive 2 by 180 degrees to give the two halves of the sinewave which seems correct.Not sure what your actual problem with the circuit is or what it is not doing. Looks very interesting though as I am sure it would not be too difficult to replace the simpler circuit in the basic MSW inverter with this one to improve the output waveform. I have a load of faulty MSW inverters under repair so I will give this a try. It should also be possible to replace the 4017 cct with a PIC microcontroller to give a higher resolution sinewave. It is possible to produce a 16 step sinewave using only 4 resistors.


John

« Last Edit: July 15, 2004, 03:27:45 PM by (unknown) »

(unknown)

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Re: Inverter schematic
« Reply #9 on: December 12, 2007, 05:25:06 AM »
The circuit diagram look very simple. I believe it should work.


One resistor is missing and that is R12. This is just a correction I want to pass across. Thanks.

« Last Edit: December 12, 2007, 05:25:06 AM by (unknown) »