Fechter IR2101 h-bridge schematic

[fitek]

Hi all,

I looked at this schematic a while back while working on my motor controller. Had a few questions:

1) What do the 22ohm/100ohm resistor and diode in parallel do?

2) What voltage is being put on "H in" and "L in" on the IR2101? What chip, IC1, is off "to the left" of the schematic?

3) What do the two transistors on the high side do? I assume they are there to boost the gate voltage of the high side MOSFET, but I thought the IR2101 is supposed to take care of that? edit: actually now I realize it's probably inverting the signal, how about that?

4) One 10 ohm resistor on each MOSFET has a floating connection. I assume this should be connected to ground?

 

[fechter]

1) the 22 ohm resistor limits the current during that microsecond of transition when both the upper and lower transistor are on. This prevents shoot through damage.

Not exactly sure about the 100 ohm / diode thing. I guess it makes the thing turn off faster than it turns on to increase the dead time which helps prevent shoot through on the FETs. It might work fine without them as the 2101 has built in dead time.

2) Inputs are coming from the CA1246 commutator chip. I think it's 12v.

3) The two transistors boost the output of the 2101. I've seen some controllers where they drive the FET gates directly from the 2101, which seems to work.

4) the floating 10 ohm goes to an identical parallel set of FETs. Not drawn for clarity.

 

[fitek]

Ah, OK, the 10 ohm thing makes sense. I sat there and scratched my head for a while.

I guess I don't need the shoot through protection at all; my controller software has it built in, and so does the IR2101. That should be plenty.

In my controller I tried to drive the FETs directly from the IR2101, but it didn't work very well. They heat up a lot and the output was very weak.

Mind you, I was using logic level on the IR2101 inputs. To do that, I had to hook the chip to 5V. The IR2101 worked better with 12v, but then the logic level on Hin and Lin is the wrong voltage (though it still sort of worked).

I purchased a CD4504 level shifting chip which I guess I need to throw in between the uC and the IR2101.

The H Bridge looks so easy in a block diagram, actually building one is a pain in the butt.