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Design of Inverter using T0-247

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sabu31

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Hi,

I have a doubt regarding Inverter Design using TO-247 Mosfets. The current rating of Mosfet is 20A. As TO-247 is PCB mounted, how can we make traces that can allow 20 A with out heating of tracks. Could somebody give links to designing inverters with TO-247 or other PCB mount packages with high currrents (20A or more).

Thanks.
 

The gate current will be relatively low and the drain/source current will be pulsed so the average will be somewhat lower than the 'on' current. Also, you mention 20A rating which is usually qualified by specifying the temperature at which it applies, that includes the pins as well as the body. On a PCB, don't forget you can use large tracks for the drain and source and optionally, more than one layer.

Brian.
 

Hi betwixt

Thanks for the comment. However, there are still mosfets for very high currents say IXTX120N65X2 which has 120A current with TO-247 package. How. is it possible to make say a two layer PCB for 3-phase inverter consisting of six such discrete switches. Because, if we design for full rating, the tracks would be large which would have to taper at the soldering points. I am confused regarding the how inverters of high rating can be made with such switches.
 

On a 1oz Copper, 18.420mm width copper track can carry 20A continous current with a temperature rise of 10 degree(According to kicad PCB calculator). You can use a expose copper area for high current conduction also.
 

IXTX120N65X2 which has 120A current with TO-247 package
Click to expand...
You are reading datasheets rather superficially. 120 A is the maximum continuous rating with 25° C case temperature. It's more a theoretical number for calculation purposes than anything that will be achieved in a real design.

As others have shown, trace heat dissipation can be calculated and trace width can be designed according to specification. Making a high power inverter on two-layer PCB with 35 µm copper plating might not be the best idea, but I don't want to anticipate your calculations.
 

FvM said:
You are reading datasheets rather superficially. 120 A is the maximum continuous rating with 25° C case temperature. It's more a theoretical number for calculation purposes than anything that will be achieved in a real design.

As others have shown, trace heat dissipation can be calculated and trace width can be designed according to specification. Making a high power inverter on two-layer PCB with 35 µm copper plating might not be the best idea, but I don't want to anticipate your calculations.
Click to expand...


Thanks FvM for the comment. I read the datasheet once again and they have shown Id Vs Temp. I noticed that the mosfet still supports 60A current at 125degree C case temperature.
I agree with FvM that making high power inverter on two layer PCB is not correct. Then why do vendors make high current mosfet with PCB mount packages or there is some other design technique to use To- 247 in high power inverter which I may be ignorant of.
 

The boards can use multiple layers for the connection, as previously suggested. They can also use thicker copper plating.
 

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