How to turn ON mosfet?

[ctag06]

In my final year project, i have to simulate full bridge inverter using PSpice. In this project, two comparators uA741 were used to give supply for the N-channel Mosfet. But the problem is, when i try to simulate my work mosfet can't turn ON because the value of Vgs for the mosfet is less than 12V. Can somebody help me what should i do to make sure this mosfet can operate properly.

 

[crutschow]

I don't understand your setup. Please post a schematic.

 

[aljamri]

or at least the MOSFET number you are using.

 

[BrownOut]

Turn on a MOSFET: low lighting, soft music and champaign...

Seriously, post a schematic.

 

[Boncuk]

Agreed with all foregoing posts.

Post your schematic and you'll certainly find a solution. (or the great community of members will direct you to the right way).

Flowers to everyone concerned with that problem!

We're the greatest!

 

[vne147]

Turn on a MOSFET: low lighting, soft music and champaign...

Seriously, post a schematic.

Very funny!

 

[ctag06]

Hi,

Sorry guys for being late to reply all the messages... I really appreciate all the responses. Here is my schematic

View attachment pwm source-SCHEMATIC1-Default.zip

 

[Hayato]

Turn on a MOSFET: low lighting, soft music and champaign...

Seriously, post a schematic.

He is in the last year and wants to know how to turn on a mosfet... I think it he is a bit late.

 

[ctag06]

Hai,

Thanks for reply. I admit that i'm too late to know about this...but i really really hope someone can help me to solve this problem.

 

[BrownOut]

Please post a .jpg or otherwise readable version of your schematic, and not a zipped version, and I'll take a look at it.

 

[audioguru]

Please post a .jpg or otherwise readable version of your schematic, and not a zipped version, and I'll take a look at it.

Please do not save your schematic and post it as a fuzzy JPG file type. Please save it and post it as a very clear PNG file type instead.

 

[ctag06]

Hai BrownOut and audioguru,

Sorry guys for my mistake...I hope this attachment could work. Anyway, thanks a lot for reply me.

 

[Hayato]

Why are you using 6 opamps?

 

[audioguru]

The inputs on the 741 opamps are not biased so they will not work. Their output high voltage is +3.5V but your lower Mosfets need a gate voltage of +10V and the upper Mosfets need a gate voltage of +180V to turn on.

 

[BrownOut]

Is there some reason you're using +/-5V for your op-amps? Is there any reason you're using all N-FET's for your bridge circuit? If your high side FET's were P-FET's then the bridge might work, but you would need to deive the gates to very near the 170V to trun them off. You would need an extra transistor on each input side to translate the voltage.

 

[ctag06]

Hello audioguru,

sorry for being late. So, what should i do with my op-amp to make sure they will work?

 

[ctag06]

Hai Brownout....

i dont have any idea why i put -/+5V for my op-amp because i really new with this part and i just lookin the source from internet and try that value...so bad right? and actually i want to use all N-channel mosfet because i'm already buy the n-channel for my project and IR2181 as it driver. I want to try your suggestion but I don't really understand about an extra transistor on each input side. using the same transistor? Can you post to me your drawing? Sorry and thanks a lot for reply me

 

[audioguru]

The lousy old 741 opamps are much too slow. While they are slowly ramping the gates of the Mosfets then the Mosfets will be quickly heating and might burn out.
Use real comparators if you want which switch much faster.

 

[ctag06]

thanks a lot for your advice. I'm really sure it will help me for my simulation stage...I'll try to use real comparators as you said. Thanks again and i really appreciate it...

 

[ctag06]

Hi Brownout....

I've tried to do the simulation like your advice....This is what do you mean?you can see the attachment. please correct me if i do wrong.

Thanks.