Steve, I agree. Seems to me that the IR2104 drivers would work for this small of a current load and they are $2.40 from Arrow and they include shoot through protection. I was going to give up on this little experiment, but judging by the PMs I have received; I plan to keep plunking along.
I have two separate designs now: a unipolar and a bipolar. I talked myself out of a D/A converter and went with PWM. Actually it needs two separate PWM modules and there are only a few PICs with two. They are pretty much pin compatible so I am trying to accommodate a few choices. The PIC16F873 seems a fair choice, but it is $4.25 at Mouser. I also ordered some brand new PIC18F24J10 from Microchip Direct for $2 each (shipping was obnoxious as they had to come from Singapore, but they say the parts will be available soon for distributor purchase) but they are a 3.3volt device so extra regulation and level shifting needs to happen. The open collector TTL inverters do the level shifting when using CMOS parts (the IR2104 is already 3.3v compatible).
Actually the charge pumps are there for the purpose of being able to drive the high side gate of an N-channel FET all the way to the top rail (or beyond). There is extra logic and a time delay inside the driver to control shoot through.
I will try to get some boards built to try it out.
Any thoughts or comments are more than welcome.
Steve |