I have a switchmode power supply in a car amplifier that uses 8 matsushita 2SD1445A-Q transistors unable to find these I want to sub
2SD2151-Q that is supposed to be a direct sub and available however some specs are not in the datasheet - Cob and hFE3 also Pc is 30W and not 40W as the D1445A is. Well thats the info I have, my question is what should I be concerned with and how will these differences effect operation at higher currents? Jeff
They will most likely work. Cob (Cbc?) is one of those "smaller is better" parameters. The ideal transistor would have zero. Newer transistors usually have less and so even if the data sheet fails to spec the parameter, the newer device will likely be better than the old device. Hfe has never been tightly controled, so all circuits intended for mass production are designed to work with transistor hfe the varies by a factor of three from lot to lot of devices. Pc (power,collector) is a function of package style. Transistor power dissapation is limited by heat. Heat is developed in the device junctions and is conducted to the ambient air thru the case. Larger cases have a lower thermal resistance than smaller ones and so can dump more heat. If the case is the same, the thermal resistance is the same and thus the power handling capability is the same. Question. How did the 8 orignal transistor happen to fail? Transistors don't wear out, they get blown out by a circuit fault. If the circuit fault that took out the original transistors is still present, the new transistors will fail just like the original ones did.
David Starr
The first failure was due to capacitors these were replaced with a type I have used before in the same model amplifiers with no problems. I have replaced these transistors before also no problems, this is the first time with this replacement part and in two amps both have been returned blown, also both were tried in the same vehicle so it can also be a problem with the vehicle but I do not have it here to check it out and have to rely on someone else if that was done. They checked out fine on the bench after repair. Thanks for the info, I hope they did not leave the specs out because they are worse! Jeff
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