H Bridge inverter can't get correct output

Thread Starter

Lauri1991

Joined Oct 20, 2013
6
Hi, I'm new in this forum and I try to figure out where's my problem.
I need to get output value 100V from load resistance, but shouldn't I need to give 100V in from DC voltage supply? And then from pulse voltage I give a input signal to the n MOSFET gate... the input signal should be 12 volts larger then the dc input signal? Or I have misunderstood everything? Can't get no solution. Please help, thank you :)
 

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R!f@@

Joined Apr 2, 2009
9,647
An Inverter takes in low DC voltage and produces the desired AC voltage.

What's the point in feeding 250VDC to produce 100VAC

Ur diagram does not makes sense.
 

Thread Starter

Lauri1991

Joined Oct 20, 2013
6
I agree with it. It is normal to have 100V DC feed to have 100V AC output. Put that is the point I have at the moment. It doesn't work with 100V feed, then the output is 68V AC ... and because it is a square wave, then the rms should be 100V. Looking still for solution, if you or someone else can help, then I'm very pleased.
 

praondevou

Joined Jul 9, 2011
2,935
You are not properly driving the upper MOSFETs. Their source need to be connected to a pulse voltage. Try setting up 4 different pulse voltages (one for each gate), the upper ones 180 degrees shifted (inverted ) with respect to the lower ones.

The way you drew it it could only work if the upper FETs were p-channels and the pulse voltage has the same maximum value as the bus voltage. (which is not the case)
 

Thread Starter

Lauri1991

Joined Oct 20, 2013
6
I had it shifted 180 degrees, I had one grammar mistake there. But I'll post it up again, with more information on the picture. If I don't understand now, then I'm a dummy.
 

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praondevou

Joined Jul 9, 2011
2,935
You are driving the MOSFET gate (voltage from gate to source) with 112V.

Your datasheet shows a mosfet driver IC that can be used up to 600V bootstrap voltage. One thing has nothing to do with the other.

600V means the upper MOSFET voltage can be up to 600V above the lower MOSFETs source. It does NOT mean you can apply 600V Vgs. This would destroy any common MOSFET.

Read this introduction: http://www.fairchildsemi.com/an/AN/AN-6076.pdf
 

Jony130

Joined Feb 17, 2009
4,931
praondevou Don't worry I know that most of a mosfet has Vgs_max in range = 24V.
I just wanted to show OP how he should drive the mosfets properly.
 

Thread Starter

Lauri1991

Joined Oct 20, 2013
6
Got it solved, with MOSFET's gate pulsing value 15V. Thank you both. But now I'm trying to solve another problem. How do I get another correct value with using function generator and a comparator instead of pulse voltage sources? I thougth that now it should be easy, but I still can't get a solution to it. To gates I apply 10 volts (in pic a comparator has 15V, it's 10 now). In the output I get Vpk(positive) = 100V and Vpk(neg) = 10V Any hints, helps? Thank you
 

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praondevou

Joined Jul 9, 2011
2,935
praondevou Don't worry I know that most of a mosfet has Vgs_max in range = 24V.
I just wanted to show OP how he should drive the mosfets properly.
Oops, I somehow assumed your post was the OPs response to my post. Sorry. :)
 

praondevou

Joined Jul 9, 2011
2,935
Got it solved, with MOSFET's gate pulsing value 15V. Thank you both. But now I'm trying to solve another problem. How do I get another correct value with using function generator and a comparator instead of pulse voltage sources? I thougth that now it should be easy, but I still can't get a solution to it. To gates I apply 10 volts (in pic a comparator has 15V, it's 10 now). In the output I get Vpk(positive) = 100V and Vpk(neg) = 10V Any hints, helps? Thank you
There is nothing connected to the sources of the upper FETs. They are not being driven correctly. That's why I said you need to use 4 independent pulse voltage sources.

Have a look at the bridge in this post:http://forum.allaboutcircuits.com/showpost.php?p=662997&postcount=5
 
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