Monthly Archives: November 2011
Yay, I’m finally documenting my Halloween costume (which unfortunately blew up the day before halloweekend). Here is a video of hatcoil, a small DRSSTC on top of a hat. AKA, a really bad idea.
28V A123 battery pack
4xHGTG 30N60B3D IGBT full-bridge with GDT drive
~1200 turn secondary on 1″ PVC
Really, it’s just a DRSSTC. Nothing less, nothing more, nothing fancy. It was a bit tricky to make a bridge appropriately sized, and even harder to make a boost converter for it. In fact, the boost never truly worked. If I play a mid to high note for a few seconds, the boost can’t keep up and it fades away. I think this is due to saturation of my boost core, but I haven’t really taken the time to do much on this since now I’m back in the gate driver world and also have to throw together my 6.131 power electronics final project. I’ll fix hatcoil in February.
The optically linked controller is an atmega328 based board which reads MIDI files off of a microSD card for playback. Thanks to my friend Jeff Heidel for assistance in getting the midi parser working.
I now hate floating gate drives and love Gate Drive Transformers (GDT). Quite the change of love! After hatcoil worked better on GDT’s and was easily transformed (more on hatcoil later), I figured why not increase the reliability of big-coil with GDT’s. I threw together a quick P-N totem pole pair board capable of driving a GDT in bipolar with no blocking capacitor (assuming 0v DC from an even duty cycle). The results are quite beautiful. I did not realize it was this easy to make a gate drive transformer work great.
Adjusting the voltage put out by the first LM317 allows for adjustment of the gate drive voltage (since this will power the P-N half bridges), and the second LM317 powers the UCC37321 drivers, which allows for adjustment of the intermediary gate drive signal level for minimal shoot through. If this gets too high, certain pairs of FET’s will severely shoot-through and over heat. The FET’s I’m using right now don’t really have an issue but I have used other models that are useless with 15V drive in this particular capacitively coupled P-Fet drive scheme.
The board was carefully routed to have basically no ground loops between output and power supply, and to have bypass caps as local to the output stage as physically possible. The results are incredible, it’s just like having a discrete driver on the brick, but there are no reliability concerns!