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  #1  
Old 02-05-2012, 07:30 AM
MatheusLPS MatheusLPS is offline
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Default IR2184 gate driver questions with IRFP460

Hello people.

I am designing an power inverter.

My idea is transform 12VDC in 120VAC@60Hz.

I will make a signal PWM at 25Khz comparing a triangle wave and a sine wave. OK.

But, to make things simpler in the beginning, I am testing with an static square wave at 25Khz provided by a 555 IC.

I threw this signal on a IR2184 gate driver to switch my two IRFP460 mosfets.

So I started with a basic circuit:



This one is working very well. I am using a single power supply with 12VDC. Look the all the power lines and grounds are the same.

The signal at my gate is ~12V. Nice:



And measuring the voltage across the resistor I came with this:



12Vp.p. It looks that is working. .

BUT.....

Lets say that I need to work with two separated power supply's. One will be my power supply for the control circuit (12V).

Lets consider that I will use another power supply with 12VDC to power the mosfets and capacitors....

So now I have two power that has different ground lines......

My problem is the COM PIN of the IR2184. Accordingly to the datasheet, I need to connect it to the ground of the "HIGH" power supply. When I say "HIGH" I am referring to the power supply that feeds the mosfets.

In this example, the power supply is 12V, but it can be 24V, 100VDC..... I do not know yet.....

I connect the COM PIN to there and what happened? My IR2184's burned... twice........

What is the correct way to connect the two power supply's and my control circuit?

bye
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  #2  
Old 02-05-2012, 03:20 PM
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praondevou praondevou is offline
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Quote:
Originally Posted by MatheusLPS View Post
Lets say that I need to work with two separated power supply's. One will be my power supply for the control circuit (12V).

Lets consider that I will use another power supply with 12VDC to power the mosfets and capacitors....

So now I have two power that has different ground lines......

My problem is the COM PIN of the IR2184. Accordingly to the datasheet, I need to connect it to the ground of the "HIGH" power supply. When I say "HIGH" I am referring to the power supply that feeds the mosfets.

In this example, the power supply is 12V, but it can be 24V, 100VDC..... I do not know yet.....
Your schematic is missing the gate resistors. The absolute maximum rating for the "IN" pin is VSS+10V. You are applying 12V.

How did you connect the 2184 when it burnt?
The 2184 has only one reference pin, COM, for logic power supply and the output side. The 21844 could have two completely separated power supplies.

For the 2184 the way you connected it is ok. Just use a different power supply for the leftmost +12V (and disconnect it from the the other 12V of course). The power supplies grounds need to be connected if using the 2184.



This application note will be helpful for you:
http://www.irf.com/technical-info/appnotes/an-978.pdf

If you are planning o use a 60Hz transformer you can use a 12V power supply for the MOSFET part.
If you plan to use an LC at the output you will need a much higher voltage for 120VAC, depending on your modulation method.
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Old 02-05-2012, 07:12 PM
MatheusLPS MatheusLPS is offline
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Well, I changed the output from 555IC to 5V, providing 5V at VCC....

Now, my third IR2184 did not burn... but when I turn ON the mosfet's power supply, only the upper one become very very hot..... and I turn it off....

I connected the circuit with two ATX power supply, like this:

P.S: I forgot to add the resistor on the gate, but on my circuit, I added two 22 ohms resistors. Each one to each gate.



bye

Last edited by MatheusLPS; 02-05-2012 at 07:17 PM.
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Old 02-05-2012, 07:40 PM
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Paul Kerry Paul Kerry is offline
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From looking at the application note above it seems to me that you have your power for the load incorrectly connected. Have a look at figure 5a. I'm no expert on this device and I could be wrong, it's just the first thing that jumped out at me
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Old 02-05-2012, 07:59 PM
MatheusLPS MatheusLPS is offline
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You are not wrong, I can connect two power supply stead of two capacitors...

The difference is that with two power supply stead two caps I have a signal at the end 24V p.p and with the caps I have a signal with 12V p.p.

bye
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Old 02-05-2012, 08:04 PM
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There is no DC return path so your high mosfet will never turn off. I suspect this is why it is getting hot. If you only want 12v use two 6v supplies
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Old 02-05-2012, 09:10 PM
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praondevou praondevou is offline
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The picture from post #2 shows exactly what you need.


1 power supply for logic and gate drive circuitry and one for the load. Both power supplies' ground connections are tied together. Why?
There is one connection from the lower MOSFETs source connection back to COM, this is necessary to drive the lower MOSFEts gate. And there is one connection from the source of the lower MOSFET to the (here) 600V power supply return.

VCC supplies the logic part AND provides voltage to the gate drive circuitry, directly for the lower part and via the diode/bootstrap capacitor for the upper MOSFET.


Also have a look at the functional diagram of the 2184's datasheet on page 4. There is only one ground for input and output, unlike the 21844.

Then you said you changed VCC to 5V?

VCC can be up to 25V above VS. IN and |SD shall be lower than VSS+10V.

Check if the MOSFETs and the halfbridge capacitors are still ok. If only the upper MOSFET gets hot then where is the current flowing through??
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