Whilst attempting to repair a simple microphone pre-amplifier for a friend, the culprit was found to be a blown transistor. A quick internet search found the specifications of the device and it was then a simple matter to find a suitable replacement from what was available in the junk box.
Interestingly, my friend, who has only a casual interest in electronics, was bemused by all the Vcb, Vce, Ic and other details in the parameter tables.
So I did a quick drawing of a simple common emitter amplifier based on a NPN transistor and explained the different values.
Interestingly, my friend, who has only a casual interest in electronics, was bemused by all the Vcb, Vce, Ic and other details in the parameter tables.
So I did a quick drawing of a simple common emitter amplifier based on a NPN transistor and explained the different values.
Below is a sample specifications table for some NPN transistors. Notice the three BC107 transistors at the bottom of the list are from two different manufacturers, but their specifications vary quite a bit. For example, the Hfe (Small Signal Gain) of the TRU device is over four times that of the CDIL variant, but the CDIL variant has a higher maximum working frequency.
The parameter that most hobbyists are concerned about tends to be the Ic. This is the maximum current that the transistor can drive when a load is connected between the Collector and +Vcc.
The parameter that most hobbyists are concerned about tends to be the Ic. This is the maximum current that the transistor can drive when a load is connected between the Collector and +Vcc.
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