Originally Posted by
jderou
Ok I hate to beat this issue to death, but I want to figure out why transistor failure is so common with the Bridgeport boss machines. Their has to be some major flaw in the circuit design. You almost never hear about it in any other machine.
The most common reason for the failure of power transistors in an H-bridge is shoot-through. This occurs when the switching times between the high side and low side transistors allow both transistors to be on at the same time. This is essentially a short to ground and it will blow at least one of the transistors.
The operating temperature of the transistor effects how quickly it will turn off. As they heat up, they turn off slower. The logic that determines when to turn on which transistors needs to allow for this.
The electronics available in the '80s were no where close to what is available now. It is likely this contributes to the problem also.
"Perfection is achieved, not when there is nothing more to add, but when there is nothing left to take away." Antoine de Saint-Exupery (1900 - 1944)