PEN NO Ahir Darshan Harsora Ashish Mistry Ravi

SNPIT&RC Education BE(DEGREE) EC WINTER-2104 B C E

The BJT – Bipolar Junction Transistor  Note: It will be very helpful to go through the Analog Electronics Diodes Tutorial to get information on doping, n-type and p-type materials. The Two Types of BJT Transistors: npnpnp npn E B C pnp E B C Cross Section B C E Schematic Symbol B C E Collector doping is usually ~ 10 6Collector doping is usually ~ 10 6 Base doping is slightly higher ~ 10 7 – 10 8Base doping is slightly higher ~ 10 7 – 10 8 Emitter doping is much higher ~ 10 15Emitter doping is much higher ~ SNPIT&RC Education BE(DEGREE) EC WINTER-2104

BJT Relationships - Equations B C E IEIEIEIE ICICICIC IBIBIBIB - + V BE V BC V CE B C E IEIEIEIE ICICICIC IBIBIBIB - + V EB V CB V EC npn I E = I B + I C V CE = -V BC + V BE pnp I E = I B + I C V EC = V EB - V CB Note: The equations seen above are for the transistor, not the circuit. SNPIT&RC Education BE(DEGREE) EC WINTER-2104

NPNPNP SNPIT&RC Education BE(DEGREE) EC WINTER-2104

Modes of Operation Most important mode of operationMost important mode of operation Central to amplifier operationCentral to amplifier operation The region where current curves are practically flatThe region where current curves are practically flatActive: Saturation: Barrier potential of the junctions cancel each other out causing a virtual shortBarrier potential of the junctions cancel each other out causing a virtual short Cutoff: Current reduced to zeroCurrent reduced to zero Ideal transistor behaves like an open switchIdeal transistor behaves like an open switch * Note: There is also a mode of operation called inverse active, but it is rarely used. SNPIT&RC Education BE(DEGREE) EC WINTER-2104

Forward bias the BEJReverse bias the CBJ SNPIT&RC Education BE(DEGREE) EC WINTER-2104

Plot I B as f(V BE, V CE ) As V CE increases, more V BE required to turn the BE on so that I B >0. Looks like a pn junction volt-ampere characteristic. SNPIT&RC Education BE(DEGREE) EC WINTER-2104

Plot I C as f(V CE, I B ) Cutoff region (off) both BE and BC reverse biased Active region BE Forward biased BC Reverse biased Saturation region (on) both BE and BC forward biased SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

KCL >> I E = I C + I B β F = h FE = I C /I B I C = β F I B + I CEO I E = I B (1 + β F ) + I CEO I E = I B (1 + β F ) I E = I C (1 + 1/β F ) I E = I C (β F + 1)/β F SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

V CC V CC /R C SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

ECE 442 Power Electronics SNPIT&RC Education BE(DEGREE) EC WINTER-2104

Input voltage rises from 0 to V 1 Base current rises to I B1 Collector current begins to rise after the delay time, t d Collector current rises to steady-state value I CS This “rise time”, t r allows the Miller capacitance to charge to V 1 turn on time, t on = t d + t r SNPIT&RC Education BE(DEGREE) EC WINTER-2104

Input voltage changes from V 1 to –V 2 Base current changes to –I B2 Base current remains at –I B2 until the Miller capacitance discharges to zero, storage time, t s Base current falls to zero as Miller capacitance charges to –V 2, fall time, t f turn off time, t off = t s + t f SNPIT&RC Education BE(DEGREE) EC WINTER-2104

Charge storage in the Base Charge Profile during turn-off SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

SNPIT&RC Education BE(DEGREE) EC WINTER-2104

Thank You 27