Using the IR2304(s) for the first time (to make a three phase inverter)

Thread Starter

1toneboy

Joined Jun 15, 2015
4
Hi,
I completed an Electrical Eng degree a couple years ago, during I took power electronics. However, I have never been big on electronics, more the power side of things.

I am currently building a BLDC controller which I may eventually just use an arduino for, but for the mean time I'm using a raspberry pi zero. But this is just background.

I'm happy with my code to interface with the hall sensors, however I'm struggling with the inverter. I first tried using three single H-bridges with a common neutral, but I don't think the control circuitry liked it. So I'm having to build my own inverter.

Using the IR2304 mosfet driver (I'm using IRF3205 NMOS). I built the attached circuit and connected it all up and it all seemed to work, however, I noticed that for the totem poles, instead of being 'high, low, off' for instance, it was always 'high, low, high'. I.e. there were always two ON, rather than the unused poles switches being OFF, the upper switch was always ON. (there is a chance it was 'high, low, low' and I misread or am mis-remembering, but you get the point)

I tried everything to get it to turn OFF, with no success. I then conducted an autopsy to see what the problem was.

The first thing I noticed was that the output to the load was Vcc, and not the 12V or 24V I was putting across the DC bus.

I then removed the three IC chip modules from the mosfets and looked at each chip output individually.

I have observed that Vs is ALWAYS equal to Vcc. I am not sure if this is supposed to be the case.
Also, VB is ALWAYS equal to Vcc. "..."

The upper mosfet, driven by HO. Doesn't HO have to be some voltage such as Vcc larger than Vs for the upper mosfet to turn ON? Because wouldn't the above point mean that the upper mosfet is always OFF if they're the same voltage?

The i/o functionality diagram on page 4, is this with reference to the COM pin?
I tested the chips circuits individually just using a multimeter, but needless to say the HO does not match the diagram if it's referenced to COM.

Notes:
I didn't use any resistor on the gate of the MOSFETS, as I have seen 22Ohms used by people. I'm not sure what the effects of this could be.
I used a 12V battery and a boost converter to output 15V to Vcc.

There is probably more observations I could say, but can't think of anything at this point.

Thanks in advance for help!

Cheers
 

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Thread Starter

1toneboy

Joined Jun 15, 2015
4
On doing some research, I read here:
https://forum.allaboutcircuits.com/threads/h-bridge-high-side-mosfet-driver.2262/page-2

in post #23:
Oh I forgot to mention that I think I now understand why the IRF2304 MOSFET driver does not work for me.

I believe it REQUIRES HIN to be pulsed, as the bootstrap capacitor only gets charged whilst HIN is low. In the start up condition of my circuit, HIN is high, as there is no current flowing in the motor, therefore my control circuit calls for the MOSFET to be switched on.

In an application note from IRF there is a circuit which uses a separate charge pump which runs whenever the HIN is high, this might be a solution, otherwise I will need some way of holding HIN low for a period at startup to allow time for the bootstrap capacitor to charge.
So maybe this is also a factor.

I'm still not clear on if Vs ever goes to GND? etc.
 

shortbus

Joined Sep 30, 2009
6,979
You might get some ideas on how it is done from the application note for the MC33035. I think the app note is AN1046 . While it is an old school way to drive a BLDC it gives a real good explanation of what the inverter does.
 

Thread Starter

1toneboy

Joined Jun 15, 2015
4
Thanks heaps for the reply Shortbus, but I'm also interested in using NMOS inverters for other future (non bldc) applications. So I'm more or less committed to the IR2304. Also the amount of time I've sunk into it, I need the satisfaction of figuring it out.

Cheers
 

shortbus

Joined Sep 30, 2009
6,979
It's been a while since I looked at this, so I may have told you to look at the wrong thing. Look up the MC33035 chip data sheet. In it look at figure 39 on page 21. And compare with how you have your H-bridges wired. Figure 39 has the H-bridges in the center right side of the drawing. This type of thing is done in many things so it is possible.
 

Thread Starter

1toneboy

Joined Jun 15, 2015
4
It's been a while since I looked at this, so I may have told you to look at the wrong thing. Look up the MC33035 chip data sheet. In it look at figure 39 on page 21. And compare with how you have your H-bridges wired. Figure 39 has the H-bridges in the center right side of the drawing. This type of thing is done in many things so it is possible.
I'll spend a bit of time looking at it, but I think it might be too dissimilar because I think it's for PMOS, NMOS configuration.
Thanks
 

shortbus

Joined Sep 30, 2009
6,979
What I meant is to look at the way it's wired compared to what you showed in post #1. You could also add a isolated DC-DC converter to keep the boot caps supplied or the is something called a charge pump that can be made. But the charge pump takes more board space and time to design.

Is there a reason that you need to do this with a microcontroller? That MC33035 is a old school way but is proven.
 
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