20 Vdc to 230 Vac Inverter Design Approach

skyflyer54 said:

Oh.. I will need a pure sinewave for my design. If I need lightweight than I can't use isolation transformer right as from what i know is that isolation transformer is very heavy. Am I right?

Can an opto_isolator be used to do the isolation between the two circuit?

By the way.. I have already done my DC DC Boost Converter (20VDC to 325VDC with 94% duty cycle) and DC AC Inverter but the problem i'm facing now is the isolation part and also the short circuit protection.

Another problem i'm facing is the deadtime problem for my DC AC Inverter. when i'm input the supply voltage for the inverter to below 20Vdc, it works well. But when i increase the supply voltage, its keep giving me short circuit problem. Luckily my supply current is not very high to the extend of burning the MOS switches. Is there a good way to implement deadtime delay for rising edge.

Another possibility i'm suspecting is that it might be noise that create the short circuit.

Any recommendation or suggestion?

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Oh... US$20 Inverters? Can I have the model number so that I can take a look at the specification?

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audioguru said:

Please explain what is SPWM.

The TL494 has its duty-cycle controled by a DC input voltage.
The output AC voltage of the inverter can be rectified, attenuated and opto-coupled to the duty-cycle input of the voltage stepup TL494 for output voltage regulation.

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Ubergeek63 said:

Using what circuit and FET? It is not typically a good idea to run high duty cycles.

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audioguru said:

I read 3 reviews of a cheap small 100W inverter by people who bought it.
Two people say it is junk. One died after powering a 10W load for 2 minutes and one overheated and was returned (but not replaced). The 3rd one still works after 6 months.

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skyflyer54 said:

Oh... I'm using MOSFET for my DC DC Boost Converter and IGBT for my DC AC Inverter.

My problem now is on the DC AC Inverter. It is a fact that the top and bottom switches cannot be turned on at the same time else short circuit will occurs due to deadtime. I have tried to put a slight delay for every turning on but it still give me the same deadtime problem when ever i increase the supply voltage.

Is there a good recommended way to implement the deadtime circuit?

Attached JPEG are the inverter design.

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Ubergeek63 said:

What frequency? most IGBTs are slow so you would need to make sure you have fast ones like IRFs warps. And at what load? They are even slower at low currents.

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audioguru said:

You like talking with letters so I looked up SPWM.
A TL494 PWM IC can make SPWM by inputting a sine-wave. It uses a triangle wave internally and comparators to create the vaying pulse widths exactly like your circuit does except it has more functions like adjustable dead time control and feedback.

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skyflyer54 said:

Oh... so you means that TL494 can address the deadtime issues?

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audioguru said:

You are confusing "shoot-through" with "deadtime".

Shoot-through is when the upper and lower transistors are turned on at the same time when one is turning off and the other is turning on. A very high current shoots through from the power supply to ground.

Deadtime is the fix for shoot-through because deatime is a pause when both transistors are turned off for a moment so that one can completely turn off before the other turns on.

Look at the datasheet for the TL494 and it is shown. All PWM ICs have a deadtime.
Are you trying to make your own PWM controller IC?

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