# pls explain this circuit in detail

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pls help me , i wasn't able to understand this circuit pls explain by the way its a modified sine inverter circuit .

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i need some clearification how it works.

thanks

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That's a lot of explanation that you want in one newsgroup post. If I'd designed a circuit like that as part of a paying job I'd expect to deliver a circuit description with 10 to 30 pages of text.

The core of the circuit consists of a switching amplifier to 12VAC, with a step-up transformer operating at line frequency (probably 50Hz). If you can't find a circuit description for it on the web I'd suggest you start doing web searches on switching amplifiers, and start working out the functionality yourself.

```--
Tim Wescott
Wescott Design Services```
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Maybe you could start by explaining which bits you do understand ?

Graham

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Well, I'ts not a particularly GOOD design. Lots of strange parts choices.

Many very good inverters have been made with about 1/20 the number of parts!

There's an op-amp and ancillary parts acting as a 12V to plus and minus

12 volt supply for the other parts.

There's an op -amp acting as an oscillator. Actually as a ramp generator. The capacitor charges through two resistors and discharges quickly thru a diode.

The CA3130 acts as a comparator (a poor one), comparing how far we are up the ramp with the output voltage. If the output voltage sags, the comparator will stay on longer, making a longer pulse.

Then the comparator output goes thrugh some logic to ensure only one FET will be turned on at a time. The logic gets amplified by some medium-power FET push-pull circuitts and drives the power FETS. Those feed a step up transformer. The output current and voltage are both monitored (poorly) and fed back to overvoltage and overcurrent amplifiers, which shut off the oscillator.

That's basically it. Lots of problems though.

(1) The whole design looks like a "paper design" for somebody's senior project. Lots of use of generic parts where simpler, cheaper, and more functional IC's are available. For example the whole bottom half of the page can be replaced by one 45 cent TL494 IC. And do more, and better. The charge-pump power supply is overly elaborate and can be replaced by one IC.

(2) There's no guarantee this is buildable. At these power levels, you need more than a schematic-- for example the transformer design is quite critical. There need to be some more safety parts added to trim transients and absorb EMI. I don't see any temperature compensation or overtemp sensors. Mounting the FETS to a proper (probably fan-cooled) heatsink is critical too.

I have no idea where one gets a 250 amp 12v to 220 volt transformer, or FETS capable of that much current.

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I really don't *want* to understand how this circuit works (if it even does). It looks like an example of many *wrong* ways to do things. Maybe that was its intent, as a learning tool. It would be helpful to know why you need to understand this circuit. It reminds me of the circuits on equipment I sometimes try to troubleshoot and repair. I have often thought it would be easier to redesign the circuit and patch it in on a perfboard rather than trying to figure out and repair a fundamentally flawed design.

In this case the preferred way to generate the output voltage would be a high frequency DC-DC converter (12 V to about 350 V), and then a PWM bridge circuit (which could produce a good sine wave with some filtering), or a simple on/off switch with deadtime for modified sine wave.

Paul

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Looks like he's got 8 FETs in parallel which helps a bit.

Not sure I'd want to hook it up to my car battery for long though.

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Hi, Tamer. Are you trying to fix this, or is this a school assignment?

Cheers Chris

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hi to all of u, thanks guys for the effort , this circuit i want to build it , iam an electronics hobbyist and i don't build any circuit unless i know the process flow of the circuit and understand it verygood, so i thought that some pros here might help explaining in detail how the circuit process goes on , so if i want to try to change anything in it .

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I wouldn't build that one if I were you, as has allready been pointed out it doesn't look like it will work.

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Problem is, these high-power circuits can be touchy. And one little wiring mistake or short circuit and all those MOSFETS go Poof!.

One transformer, two transistors, two resistors, two capacitors, and voila, a usable inverter. For a basic schematic, see the bottom schematic in:

The circuit you asked about looks like trouble with a capital T, that ryhmes with pee, and that's what you'll be when it goes up in smoke.

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motorola actually makes a really good set of documents on inverter design, however their impossable to find, especially because they restructure their documentation authorities every so often, I only have a printed copy.

but, may I suggest throwing some newer technology at it?

I'v been mulling over a 4kW UPS design for running my house (the hot water, stove dryer etc is on gas, so no huge power demand)

what I'm thinking so far is this

48v bank -> dc-dc converter -> modulator -> filter ->

here is why..

48V battery bank: this voltage is still somewhat sane, and yet high enough to keep currents down to something sane at 4kW

approximitly:

4000/48 = 83A

if it were 12V:

4000/12 = 333A

which is getting quite scarry. also if the drive to keep it as efficient as plausable, you want to keep currents down, so your I^2R losses are lower.

,001 ohms of wire * 83 amps ^2 = 6.9W (now imagine at 333A :) )

DC-DC converter:

this is to boost the 48V to 170V (my output goal is 120V, not 240)

As a switching converter, these can be quite efficient and are still somwwhat easy to build, I'd be going for a boost converter, non-isolated. Because there is no way its practical to do this in 1 converter, it would be done with a set of converters (say 10) which makes the core of each one obtainable, and keeps for current for each converter reasoanable. The other advantages of splitting it up are that I can offset their timings, in effect a 10 phase converter, this eases life on capacitors etc etc. splitting it up also allows for some redundancy, if a converter decides to bite the buscut, it can be isolated and life can go on (which may be where the system goes into a chain reaction failure, but thats what microcontrollers are good for detecting) it also means I only have to design 1 converter and make it

10 times. This would be FET based, possibly IRF1404 or soemthing

modulator:

the 170V is perfect for bring modulated into a sine wave to form

120Vac, this would be done via pwm, making the process nicly efficient, probably PWM at a freq of 25 to 50Khz. This would probably be fet based also, although at these voltages, bipolars usaully prevail efficiency wise (high voltage fets tend to have a high Ron, a bipolar transistor has a fixed saturation voltage, there is a point that the I^2R losses exceed the IV losses)

filter:

this would be a low pass so that the pwm freq dosn't get through, just a nice true sine 60Hz.

Another nice thing is that this circuit is easily made on a small scale for testing with a 40W lamp :)

dan

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A much simpler way to go from batteries to AC power is with a few FET switches, no transformer.

Just have 16 12V batteries or so, then a bunch of FETs to connect them in parallel for a bit , that gives you a 12 volt step on the sine wave, then another set of switches to connect them two in series for a bit, that gives you 24 volts, etc, etc, etc, until for the peak of the sine wave you have all of them in series. Same thing for the rest of the sine wave.

Maybe add a small LC filter on the output to filter out most of the harmonics.

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Actually I've had good luck making high-current transformers by using old microwave oven transformers. I just cut out the high voltage windings with a hack saw, insert some small gauge wire and end up with a custom low-voltage, high-current transformer.

I've been able to get over 400 amps with a few turns or over 100 amps at 12 volts with a 1500 VA transformer. Using such a modified 3000 VA microwave transformer the inverter in this post could possibly be made.

Dorian

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The only problem with this method is that your batteries will be drained at different rates. To charge them will require an equalizing charge (overcharge) which can adversely impact battery life.

In theory its a good idea though.

Dorian

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question, did you knock out the shunt blocks on the microwave transformers or leave them in???

dan

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