hardym wrote:I could not read the .sch file in Eagle. What software are you using?
I'm using Eagle 6.1.0 - Maybe you're using an older version?
1. High side gate drivers need to generate a voltage above vcc. Typically they use a simple charge pump. Jeremys ckt uses an isolated dc-dc converter. while it works just fine, but it's not economical. A regular IRC high-side driver would have worked just fine.
I believe I have fully implemented this, but let me know if this is not the case. I think you're just saying I don't need the isolated dc-dc converter?
2. As I was told several times by jeremy, the Caps are critical. They are NOT to increase the current to the drive, but to protect the FETs from overvoltage. The Rubycons electrolyics paralleled with very fast acting caps are critical. All good controller have both.
I've spec'd these caps
with an ESR of .047 ohms. I think they will work? Do they need to be paralleled with additional caps (they are already paralleled with a few caps, as shown in the schematic)?
3. The TO=235's are supposed to provide a lot of current. I think the real issue is heat and forward resistance. Putting several TO-220s in parallel is probably more efficient for high current, but you need to deal with switching.
Not sure what you're trying to tell me with this? Use several TO-220 MOSFETS in parallel instead of the TO-235?
4. Analog monitoring of current is tricky -- need to be able to monitor current in both directions. Best to carefully copy a successful implemetation.
Not sure what you're trying to tell me. Are the shunt resistors a bad/poor choice?
5. As you may expect, brawn boards are tremendously noisy.
Suggestions on how to reduce this noise besides the parallel caps you mentioned? Or is this just a undeniable fact of any brawn board?
6. The brains needs to be well thought out. I'll be happy to supply the successful software work i've done with the PIC 18F2431, and was able to drive down the street. It seems like this PIC it has everything... but is just short one analog input pin to be perfect. The SMT version would be perfect, but you need to burn it onto a pcb to find out.
For now, I'm just using the MC33033 like Jeremy did. That should work just fine, right?________________________________________________________________________________________
Jeremy Harris wrote:The high side drive can work OK with the bootstrap option for the NCP5181, but not with the simple MC33033 chip I used. The bootstrap needs a pulse at power on to charge the cap so that the top FETs can turn on, and it's random as to whether or not it gets one, I found. More often than not I'd need to spin the motor to get it to start, just by cycling through a couple of Hall transitions, so charging the bootstrap caps. I did a lot of playing around to try and get the controller to start reliably before getting frustrated and resorting to the DC-DC converters. These fixed the start up problem for good.
Ah, so I do need the dc-dc converters after all. Thanks.________________________________________________________________________________________
I appreciate your help thus far! I hope you can provide some answers/clarification to my questions above. Thanks!