| ??? 10/20/04 01:38 Read: times |
#79599 - RE: driving power mosfet, gnd potential Responding to: ???'s previous message |
Abdul said:
When I drove via opto coupler, I attached an 100W light bulb (resistive load) the circuit worked for few minutes, after that MOSFET became shorted between drain and source. Keep in mind, that a lamp is NOT a true resistive load, but a PTC! And don't forget the very high inrush current! A typical inrush current plot looks like the following:  Under certain circumstances inrush current can lead to enormeous overheating of your MOSFET, especially if your MOSFET is not driven fast enough, means, if traversing of SOAR via forbidden path lasts too long. Use a much faster opto than you did. 6N136 might be appropriate. Use also a special MOSFET driver, which is able to charge and discharge gate capacitance fast enough. Some paralleled 4049 gates could be used for instance, also a simple VMOS driver consisting of two BSS110 e.g. By the way, it's not necessary to drive opto LED via ULN2003, as only up to 20mA need to be sinked... Kai |
