BJT (Bipolar Junction Transistor)

Types of Transistors

Power Transistor Structure

Steady State Characteristics of Power Transistor

OUTPUT CHARACTERISTCS

TRANSFER CHARACTERISTICS

SWITCHING CHARACTERISTICS OF BJT

When the base current is applied, a transistor does not turn on instantly because of the presence of internal capacitance.

At time t1, input voltage VB is made +V1and IB rises to IB1. 

After some time td called delay time, the collector current rises to 0.1ICS this delay time is required to change the base emitter capacitance to VBES=0.7V. This delay time td is defined as time during which the collector current rises from 0 to o.1Ics and collector –emitter voltage fall Vcc to 0.9Vcc.

After delay time td, collector current rises from 0.1Ics to 0.9Ics and VCE fall from 0.9VCC to 0.1 VCC in time tr. This time tr is known as rise time which depends upon transistor junction capacitance. The rise time tr is defined as the time during which collector current rises from 0.1 Ics to 0.9Ics. This shows the total turn on time ton=td+tr.

SAFE-OPERATING AREA

• Forward biased safe operating area

• Reverse biased safe

ADVANTAGES OF BJTs

•Have high switching frequencies.

•Turn-on losses are small.

•Controlled turn-on & turn-off characteristics.

•No commutation circuit required.

DEMERITS OF BJT

• Drive circuit is complex.• Has the problem of charge storage.• Has the problem of second breakdown.• Cannot be used in parallel due to