محاظره 6-7.pdf

The Power BJT: Bipolar Junction Transistor BJT is the first SCSD to allow full control. Subsequently, many other devices (that over perform BJT) classified as “Transistors” have been developed. They have almost completely replaced BJTs. The construction and operating characteristics of a Power BJ...

The Power BJT: Bipolar Junction Transistor BJT is the first SCSD to allow full control. Subsequently, many other devices (that over perform BJT) classified as “Transistors” have been developed. They have almost completely replaced BJTs. The construction and operating characteristics of a Power BJT differs significantly from the signal BJT due to the (V and I) ratings requirements. In the cutoff region (iB ≤ 0) and the collector current is almost zero. The maximum voltage between collector and emitter under this condition is denoted by VCEO (the rated voltage). Power transistors have very small reverse voltage withstanding capability  Power Bipolar Junction Transistor(BJT) To emulate an ideal switch, the base current in the on- state must be high enough for the operating point to lie on the hard saturation line associated with the lowest voltage drop across the device. BJTs cannot block negative collector–emitter voltages. To block negative voltage a diode connected in series with the collector. The second breakdown occurs when both the collector– emitter voltage and the collector current are high, that is, during the turn on or turn-off. As a result high power loss, local hot spots appear in the semiconductor. The current density increase in hot spots and leads to damage  BJT Characteristics Current-Controlled Device Low current gain compared to signal amplifiers 10