Phase 8: H-bridge rev 3

HOME


After letting a lot of smoke out of the HIP4081a full-bridge driver IC's that I was using on the Modus bridge, I decided to take matters into my own hands and design a completely new bridge driver circuit. The HIP's were costing me $7 each and I've already let the magic smoke out of 6 of them, so it was starting to get a bit discouraging. The new design takes advantage of a half-bridge driver IC with adjustable dead time to (hopefully) eliminate the amount of time that the FET is in the dreaded triode region. So far, it looks promising, but the tiny LM5105 packages are so small that it is difficult to get them soldered to my prototype PCB. After a bit of trial and error, I managed to get two of them soldered down correctly and the board is working as designed. I still have some tuning to do on the dead-time, but I'll need a much faster scope to capture what I'm looking for in the timing. This little guy can handle 30 amps with the heat sinks installed and lots of moving air, but I have not taken it up that high yet. I'm still trying to figure out where I can get a 100v 30a power supply!

Here is the bare PCB right after I finished drilling it. Due to the miniature pads that were necessary on some of the components, I decided to use the photo-etch process rather than toner transfer on this one. The board really turned out great.

 

When the production boards are built, I'll use 4 or 6 oz copper clad, but for now, I can get by with the 1 oz pre-sensitized PCB material. This is the back side of the board.

 

After a bit of stuffing.

 

The logic supply provides a smooth 5 and 12 volts to the necessary components on the board.

 

The board all stuffed and ready to go. The pins on the bottom are so I can plug this unit right into my breadboard. The FET's are mounted backwards so the heat sink can make contact with the tabs. The small trimpot is the adjustment for the onboard current limiter that is built into the design. The current limiter works extremely well and looks quite promising for the production version of the board.

 

With heat-sinks installed.

 

I only drilled one heat sink just for fit-up. Since the design is still in flux, I didn't want to make things too permanent.

 

Ahh, the elusive FET drive section. This really has taken some careful thought and engineering work to perfect. No wonder N-Channel H-bridge drives are so complex.

 

Of course it wouldn't be complete without a blue wire or two!