critique my circuit with some questions

[lokeycmos]

hello, im planning on building an inverter. i found a simple schematic(attached). ive made a few unique changes and am looking for a critique. i am upgrading the small transistors with some 200GAL173D IGBTs. they are rated for 1700v and 220A. one important question i have is, on the datasheet of the IGBT the max gate voltage is 20v. now i cant figure out if i put 12 volts to the gates from the output of the IC, will the IGBT be turned on sufficiently to stay within saturation voltage? also on another post someone said i dont even need gate resistors because IGBT gate work on voltage not current. is this true or do i need some sort of resistor? incase you need them i have the datasheets for the IC and bricks attached. one more thing, what would be a good starting value for the inductor? thank you!

 

[chemelec]

It will be Square Wave Out, Not sine wave as shown.

But you don't have any Transient Protection for the Mosfets?
Not a very Practical Circuit.

 

[Mike odom]

On the IGBT data sheet, the second section labeled IGBT shows the VGE (th) threshold voltage max is 6.2V, so, yes, 12V will turn them on sufficiently.

However, just below that, Rce (resistance of the collector to emitter) and VCE (sat) are both spec'd at Vge of 15V, so the on resistance and the saturation voltages may be a little higher, which means the gates will dissipate more power and need a larger heatsink to drive max current through them.

The data sheet shows a VGE leakage current of .1 to .3mA (VGE = 0V), and the 4047 will output approx. 2.4mA, and there is no other Ige listed for on value, so it's probably safe to assume this part will drive the gates ok. The resistors are good to stop ringing noise in the gates as they have a high capacitance value, although 470 might be larger than needed. The best value will be found through experimentation in the lab.

I don't know what frequency you're trying to obtain, probably 50Hz? But I don't like RC's for frequency generation. They have a large drift over temperature. Just my opinion...

The inductor? That would depend on the switching frequency and the inductance of the transformer...

 

[Mike odom]

I was just looking over the IGBT data sheet again, and noticed it will not work in the schematic you have... if you notice, the two drivers in the schematic are hooked emitter to emitter, but the IGBT driver is connected emitter to collector....
you would need two of the GAL models, or use a high side driver for the top transistor. But grounding the collector of the bottom IGBT would not work...

 

[audioguru]

I was just looking over the IGBT data sheet again, and noticed it will not work in the schematic you have... if you notice, the two drivers in the schematic are hooked emitter to emitter, but the IGBT driver is connected emitter to collector....

No.
Both IGBTs are low side. They turn on one at a time to apply a ground to the winding of the power transformer. The center tap of the transformer winding connects to +12V.

 

[Mike odom]

No.
Both IGBTs are low side. They turn on one at a time to apply a ground to the winding of the power transformer. The center tap of the transformer winding connects to +12V.

yes, I see you are using GAL types, not the GB. This is good...

 

[ChrisP58]

Are you still running the inverter on 12 Volts? If so, IGBTs are a poor choice for the switches. With a Vsat of almost 4 volts, you will be wasting a lot of your input power in the switcfhes.

A good, low rdson mosfet would be a much better choice.