Alan B
100 GW
Great comments.
I'm trying to decide where to locate my drivers. I have two boards stacked. The upper board is FETs and all the high voltage items. The lower is CPU and all the 5V stuff. There is a 24 pin connector mating the two boards. Components on both boards facing away from the other board.
I would like to keep the six FET board almost completely copper. Top side +V and bottom side GND. Fets at the edges along two sides. Phase wires located right at the paired driver FETs, with a chunk of copper flood connected to cool the TO247 pins feeding the phase wire.
As we have seen in the "Best Controller" discussion (which I just reread), one key to TO247 performance is cooling the pins. The pin cools the bond wires, and the bond wires are the weak link. To cool the pins we need close fitting holes to a cool copper surface. Heating in the copper surface is very bad since it heats the pins, we need current to not heat the copper, and the copper area heatsink to help cool the pins. The main way to do that is to avoid traces per se and have the FETS land in copper fill as much as possible.
So this implies that I don't want much else on the FET board. There are a few things that belong there - the interboard connector, the 70V to 12V switching regulator, the capacitors of course, and the shunt. These must be on the FET board to handle the high voltage, which should never enter the processor board - except that it has to if the driver chips are there...
The drivers can go on either board. If we move them to the FET board we loose room for copper. We also increase risk since we might want to change drivers and the FET board has more expensive components and more copper and maybe even more layers, so it is the costly board to change. We want to control risk by making the FET board right on the first spin if at all possible. But it is nice to keep all the HV on the FET board. Hmmm.
So should the drivers be on the FET board, or on the controller board right next to the connector. The distance will change by maybe an inch or so to the FET gate.
I'm trying to decide where to locate my drivers. I have two boards stacked. The upper board is FETs and all the high voltage items. The lower is CPU and all the 5V stuff. There is a 24 pin connector mating the two boards. Components on both boards facing away from the other board.
I would like to keep the six FET board almost completely copper. Top side +V and bottom side GND. Fets at the edges along two sides. Phase wires located right at the paired driver FETs, with a chunk of copper flood connected to cool the TO247 pins feeding the phase wire.
As we have seen in the "Best Controller" discussion (which I just reread), one key to TO247 performance is cooling the pins. The pin cools the bond wires, and the bond wires are the weak link. To cool the pins we need close fitting holes to a cool copper surface. Heating in the copper surface is very bad since it heats the pins, we need current to not heat the copper, and the copper area heatsink to help cool the pins. The main way to do that is to avoid traces per se and have the FETS land in copper fill as much as possible.
So this implies that I don't want much else on the FET board. There are a few things that belong there - the interboard connector, the 70V to 12V switching regulator, the capacitors of course, and the shunt. These must be on the FET board to handle the high voltage, which should never enter the processor board - except that it has to if the driver chips are there...
The drivers can go on either board. If we move them to the FET board we loose room for copper. We also increase risk since we might want to change drivers and the FET board has more expensive components and more copper and maybe even more layers, so it is the costly board to change. We want to control risk by making the FET board right on the first spin if at all possible. But it is nice to keep all the HV on the FET board. Hmmm.
So should the drivers be on the FET board, or on the controller board right next to the connector. The distance will change by maybe an inch or so to the FET gate.