Y my mosfets are blowing up????

For highside or lowside, I have to be honest I have no idea how these kind of motors work. All what I know is that the upper mosfet and lower mosfet must not turn on same time. If they don't turn on same time this will practically work.

Regarding charge pump capacitor... This is needed to reach same input gate voltage as high as 200V in your case for a short amount of time only just to help mosfet go "ON".

Your transistor cannot be 2N3903 because 2N3903 only support till 40V. I only showed an example not your actual circuit. You must find same NPN that can handle at least 200V. Maybe a FJN13003 would do the trick.

Take note using transistor is more expensive than using only capacitor charge pump. In my experience charge pump is what I know and commonly use. But transistor driven MOSFET should also work. I have seen working units as such but never selfbuilt.

Mount heatsink for MOSFET. Before pluging everything on the mosfet try measure first the outputs of the transistors (Collector to ground) If it is turning on and off properly. If so then connect your MOSFETS to a nice heatsink. Goodluck tell me if it works

Cheers
Franz :)
 
Charge pump

How it is connected...

http://datasheets.maxim-ic.com/en/ds/MAX620-MAX621.pdf


Patents...
http://www.freshpatents.com/-dt20090115ptan20090015318.php

http://www.patentstorm.us/patents/6856177/description.html

Do more research on charge pump it can save you time since capacitor and resistors are much easier to find and buy than extra transistors. Either way will work. Your IC must support Charge pump capacitor. Because these kinds of ICs like IR2118 support them and make MOSFET work cool and minimal switching loss in my experience. Minimal switching loss means less heat.

Simply choose what works best for you :)
 

Thread Starter

onlyvinod56

Joined Oct 14, 2008
369
what is the exact meaning of high side and low side mosfets?

I found a mosfet driver in google MIC5011
http://www.micrel.com/_PDF/mic5011.pdf

It can be used as both high side & low side.
Can i use six individual ICs for my mosfets? they are having the charge puymping capicity.

And Im always confused with this 3 phase inverter.
As far as my knowledge concern, firing pulses should be given to the gate w.r.t the source of that particular mosfet....right?

check the attachment, which schematic is correct?
 

Attachments

Highside means you use positive side to switch...
Easy example (Supply..Switch..Lightbulb)

lowside
+ __________/______ to bulb
- _________________ to other pin of bulb

highside

+__________________to bulb
-__________/_______ to other pin of bulb

When using a switch or relay this is mostly irrelevant. But transistor behave differently.

Yes you can use that IC. IR2118 can also be used. This you can connect at same time without having to worry about shoot-through or internal short circuit

http://www.irf.com/product-info/datasheets/data/ir2117.pdf
 

Thread Starter

onlyvinod56

Joined Oct 14, 2008
369
Highside means you use positive side to switch...
Easy example (Supply..Switch..Lightbulb)

lowside
+ __________/______ to bulb
- _________________ to other pin of bulb

highside

+__________________to bulb
-__________/_______ to other pin of bulb

When using a switch or relay this is mostly irrelevant. But transistor behave differently.

Yes you can use that IC. IR2118 can also be used. This you can connect at same time without having to worry about shoot-through or internal short circuit

http://www.irf.com/product-info/datasheets/data/ir2117.pdf

ok fine. And thanQ.
Then what about the figures in my previous post?
which one is correct between them?
 

Thread Starter

onlyvinod56

Joined Oct 14, 2008
369
Are they out of phase? Because they must be out of phase! or SHORT-Circuit!

ya. its a three phase inverter. The midpoints of the three legs will have three different phse voltages.

can u get any example for this situation.
I have six pulse trains coming out of the main IC.
These six pulse trains are isolated with 4N35 couplers.
Now my doubt is how to connect these pulse trains to the mosfets concerned?

Common ground I believe is more correct.
Can u support ur statement plz...
I think its not correct. Bcoz, If we have a common ground, the three mid points will gets short circuited as the high side mofets sources will have different phasevalues
 
Okay in your schematic you must have a 0V. Meaning Dual supply or Center Tap. The red suppose to be a +V and the Blue -V.. Then you have a center which is 0V or ground. This 0V you can use as reference to your input gates.

In short both drawings I think will not work. Your signal reference suppose to be to ground.
See my example circuit.. It's something like a push pull except you should do yours with a MOSFET. I do not have any mosfet model for multisim. Plus only use the connection as reference purpose only do not use the resistors nor voltages. The circuit is only for reference so you get the idea...

Each Transistor has a certain firing sequence. Up and Lower must be 90 deg out of phase! Some drivers have Q and Q (With bar on top) to avoid short circuit! That is what you need. If you have with complementary output driver this is good to ensure up and lower do not fire at same time!

Next issue is...
So now you must need a circuit that will do the timing that spread each firing sequence by 120 deg between R S and T or equivalent timing. Some inverter use steps some don't. I am no inverter expert for 3 phase... I have done stuff like this for single phase though. Driving an AC electric fan with variable Frequency.

Next is variable timing circuit...
This is to adjust how fast you want the motor to turn...
 

Attachments

Last edited:

Thread Starter

onlyvinod56

Joined Oct 14, 2008
369
sorry franzschluter, i have a problem with my internet modem. now its ok.

And sorry again, you have done so much work for me. I have the idea of single phase inverter. But it is completely COMPLETELY different from 3 phase inverter. I have designed push pull inverter with centre tapped transformer.

Its a coincidence, In your example circuit, both the firing pulses are not given form a 0V. Its not the fact i think..... the pulses are given w.r.t the transistor's emiter (i.e., w.r.t the source's of the individual mosfets).
luckily both the emiters (sources) are connected to zero volt point.

and the main IC HEF4752 is ready with its pulses (three sequences with 120 deg displaced). The speed of the motor can be controlled with this main IC. It is having two control pins FCT & VCT. With that both, i can control the speed.
 
Yes depending if you have 220V delta or 380V Y.. In any case you would need the 0V reference some call it PE (I think). And a transformer on your supply. See schematic...

Difference between 3 phase and Single Phase is...
1. Voltage
2. Phase (120 deg)


My simulator has no support for mosfet drivers... That's why I had to use basic components just to show my point. I have 0 volts in my circuit. Node 4 is 0V.. Line 1 is +5V Line 2 is -5V.. This is only single phase.. For three phase you need three of these.. With each line 200V with respect to ground. I think you can also use +100VDC and -100VDC.. So peak to peak is 200VDC with respect to its complementary line..

R - S = 200V difference 120deg apart
S - T = 200V difference 120 deg apart
R - T = 200V difference 120 deg apart

R - 0V = 100V difference
S - 0V = 100V difference
T - 0V = 100V difference


In your design.. Since you use MOSFETs making a sine wave is somewhat difficult. It's rather a bipolar rectangle wave in reality. With the help of a couple capacitor of big capacitors you can smoothen the edge a bit which helps the motor begin to
turn. A pure and very sharp edge is not what you want in your design. And will stall your motor.

Expensive inverters have stepping integrated.

In any case I have drawn a schematic diagram for you on how it should "basically" work.. The polarities of the MOSFET is as is. The "collector" side is either at +100VDC or -100VDC.

To drive them you need a driver which runs with a charge pump capacitor to get timing right.. To figure out this value you must know in what frequency range you intend to make it work. :D

It is like a gasoline engine.. The piston have a firing sequence. The same is with these 3 phase inverters. Which timing is required I can only vaguely imagine...

Things what can make your MOSFET go hot is the following criteria..

-Load
-Switching Loss
-Shoot-Through (When upper and lower turn on at the same time. Q7 and Q8 in my diagram)
-Wrong firing sequence which makes motor stall and suck a huge amount of current.
-Insufficient Cooling
-Insufficient Gate drive Voltage.. When datasheet says VGS=15V.. You cannot go below 15V and give 6V for example. This will only open half on and is not good for MOSFET life. :D

Cheers
Franz
 

Attachments

Last edited:

Thread Starter

onlyvinod56

Joined Oct 14, 2008
369
Yes depending if you have 220V delta or 380V Y.. In any case you would need the 0V reference some call it PE (I think). And a transformer on your supply. See schematic...

Difference between 3 phase and Single Phase is...
1. Voltage
2. Phase (120 deg)


My simulator has no support for mosfet drivers... That's why I had to use basic components just to show my point. I have 0 volts in my circuit. Node 4 is 0V.. Line 1 is +5V Line 2 is -5V.. This is only single phase.. For three phase you need three of these.. With each line 200V with respect to ground. I think you can also use +100VDC and -100VDC.. So peak to peak is 200VDC with respect to its complementary line..

R - S = 200V difference 120deg apart
S - T = 200V difference 120 deg apart
R - T = 200V difference 120 deg apart

R - 0V = 100V difference
S - 0V = 100V difference
T - 0V = 100V difference


In your design.. Since you use MOSFETs making a sine wave is somewhat difficult. It's rather a bipolar rectangle wave in reality. With the help of a couple capacitor of big capacitors you can smoothen the edge a bit which helps the motor begin to
turn. A pure and very sharp edge is not what you want in your design. And will stall your motor.

Expensive inverters have stepping integrated.

In any case I have drawn a schematic diagram for you on how it should "basically" work.. The polarities of the MOSFET is as is. The "collector" side is either at +100VDC or -100VDC.

To drive them you need a driver which runs with a charge pump capacitor to get timing right.. To figure out this value you must know in what frequency range you intend to make it work. :D

It is like a gasoline engine.. The piston have a firing sequence. The same is with these 3 phase inverters. Which timing is required I can only vaguely imagine...

Things what can make your MOSFET go hot is the following criteria..

-Load
-Switching Loss
-Shoot-Through (When upper and lower turn on at the same time. Q7 and Q8 in my diagram)
-Wrong firing sequence which makes motor stall and suck a huge amount of current.
-Insufficient Cooling
-Insufficient Gate drive Voltage.. When datasheet says VGS=15V.. You cannot go below 15V and give 6V for example. This will only open half on and is not good for MOSFET life. :D

Cheers
Franz

thanQ franzschluter,
u helped me alot. i'll start modify the circuit with the drivers.
it may take around one r two days 2 develop it.
If i celebrated the new year :D, then we will have a chat again;).
bye. again thanQ
 
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