PREPARED BY:NIKHIL KUSHWAHA(10M212)

SURYAKANT SHUKLA(10M252)

Power Bipolar Junction Transistor

Power BJT

Outline

• History• Theory• Transistor Types• Characterstics of BJT• BJT applications• Power transistor and applications• Summary• References

Power BJT

History of the Transistor

P-N JunctionRussell Ohl 1939

First TransistorBell Labs 1947Shockley, Brattain,and Bardeen

First Solid StateTransistor - 1951

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Replica of first Transistor

Bell LabsDecember 23,1947

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Processor development followed Moore’s Law

The number of transistors that can be placed inexpensively on an integrated circuit has doubled approximately every two years

Moore's law precisely describes a driving force of technological and social change in the late 20th and early 21st centuries.

Power BJT

Introduction

NPN BJT with forward-biased E–B junction and reverse-biased B–C junction

A BJT consists of three differently doped semiconductor regions, the emitter region, the base region and the collector region. These regions are, respectively, p type, n type and p type in a PNP, and n type, p type and n type in a NPN transistor. Each semiconductor region is connected to a terminal, appropriately labeled: emitter (E), base (B) and collector (C).

Power BJT

Power Transistors

• Generally– Fabrication differences for dissipating more heat– Lower gain than signal transistors• BJT– essentially the same as a signal level BJT

• MOSFET– base (fly back) diode– Large current requirements: use parallel MOSFETs

Power BJT

Power BJT

Transistor Switching Times

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CharacteristicCommon

BaseCommon

EmitterCommon Collector

Input impedance Low Medium High

Output impedance Very High High Low

Phase Angle 0o 180o 0o

Voltage Gain High Medium Low

Current Gain Low Medium High

Power Gain Low Very High Medium

•1. Common Base Configuration - has Voltage Gain but no Current Gain.• •2. Common Emitter Configuration - has both Current and Voltage Gain.• 3. Common Collector Configuration   -   has Current Gain but no Voltage Gain

Power BJT

Common-Emitter NPN Transistor

Forward bias the BEJ

Reverse bias the CBJ

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Input Characteristics

Plot IB as f(VBE, VCE)

As VCE increases, more VBE required to turn the BE on so that IB>0.

Looks like a pn junction volt-ampere characteristic.

Power BJT

Output Characteristics

Plot IC as f(VCE, IB)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

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Transfer Characteristics

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Transistor Operating Point

B BEB

B

CE CCC

C C

CE CC C C

V VI

R

V VI

R R

V V I R

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Operating Point

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Maximum ratings of Power Transistors

Device Circuit Symbol Voltage/current ratings

Upper operating Frequency(kHz)

a) BJT 1400V/400A 10.0

b) MOSFET {n- channel}

1000V/50A 100.0

c) SIT 1200V/300A 100.0

d) IGBT 1200V/500A 50.0

Power BJT

BJT Vendors

•API Electronics Inc. {High Reliability BJT, QPL Power Transistor Manufacturer}

•Central Semiconductor {Small Signal BJT, Power transistors}

•Continental Device India Limited "CDIL" {General Purpose-Medium Power-Switching-High Voltage-Low Frequency-RF-Darlington-Power Transistors}

•Diodes Inc. {Bipolar - Darlington - Prebiased Transistors, Low Saturation Transistors-Medium Power/High Voltage Transistors-Darlington-RF-Avalanche Transistors-Multichip Transistors-Low saturation Bipolars}

•Ericsson {RF Power Transistor Manufacturer}

•Infineon {RF 'BJT' Transistor Manufacturer}

•Linear Integrated Systems {Transistor Manufacturer}

•Micro Electronics Corp. {Transistor-To92/To-18/To-220/Metal Can/MT-42}

Power BJT

APPLICATIONS Because power semiconductors have very wide-ranging applications, the most desirable type for a given application comes down to several factors: the amplification, the switching speed, and the power class. Trends in particular types can be seen in applications in industry, the consumer market, and transportation

A. Industrial Applications

Within industry, the two main uses for power semiconductors are for motor control and power supplies. For motor drives, power semiconductors can control all sizes of motors from those found in large mills to simple machine tools.

B. Consumer Applications

In the consumer market, power semiconductors can be found in audio amplifiers, heat controls, light dimmers, and again in motor controls.

Power BJT

Application of the BJT Detector for Simple, Low-Cost, and Low-Power Alpha-Particle detection Systems

Power BJT

Photograph of the system assemblyBlock diagram of the readout electronics.

Power BJT

In the recent past, a high-resistivity-silicon detector with internal signal amplification based on the bipolar transistor (BJT) effect is developed. The operating principle isanalogous to that of the phototransistor, widely employed for detecting light. With the base left floating, the high-resistivity substrate (that acts as the collector region for the BJT) can be depleted by a positive voltage applied between collector andemitter terminals. The hole charge generated by an ionizing event is collected on the base, then injected as a forward current toward the emitter, thus causing a much larger electron current to flow between emitter and collector. The time integral of the resulting emitter-current pulse amplifies the signal charge by a factor equal to the current gain (βF) of the transistor. BJT detectors with peak βF up to 600 were inparticular fabricated, allowing for radiation detection with a very simple readout setup . Owing to its intrinsic noise and speed limitations , the BJT detector can not be applied when demanding resolution and counting-rate specifications are required, yet it is well suited if simplicity and low cost of the readout electronics are the primary goals. In order for its internal signal amplification capability to be fully exploited,the BJT must generally be biased at a convenient quiescent current. This can either be done by LED illumination or by base-current injection through a large-value polysilicon resistor or an integrated pnp transistor acting as a currentsource [6]. In any case, power consumption and system- or device-level complexity increase.

RDFC Applications

Power BJT

This application note provides key parametric requirements of power BJTs suitable for resonant Discontinuous Forward converter (RDFC) applications. As the main power switch, the BJT will undergo different stresses in RDFC compared to hard switching opologies such as flyback. Selecting the correct BJT is vital to obtain optimal power supply performance and meet safety requirements. Typical RDFC Application Circuit

Advantages

The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are

•Small size and minimal weight, allowing the development of miniaturized electronic devices.•Highly automated manufacturing processes, resulting in low per-unit cost.•Lower possible operating voltages, making transistors suitable for small, battery-powered applications.•No warm-up period for cathode heaters required after power application.•Lower power dissipation and generally greater energy efficiency.•Higher reliability and greater physical ruggedness.•Extremely long life. Some transistorized devices have been in service for more than 50 years.

Advantages

The key advantages that have allowed transistors to replace their vacuum tube predecessors in most applications are

•Small size and minimal weight, allowing the development of miniaturized electronic devices.•Highly automated manufacturing processes, resulting in low per-unit cost.•Lower possible operating voltages, making transistors suitable for small, battery-powered applications.•No warm-up period for cathode heaters required after power application.•Lower power dissipation and generally greater energy efficiency.•Higher reliability and greater physical ruggedness.•Extremely long life. Some transistorized devices have been in service for more than 50 years.Power BJT

Limitations

•Silicon transistors do not operate at voltages higher than about 1,000 volts (SiC devices can be operated as high as 3,000 volts). In contrast, electron tubes have been developed that can be operated at tens of thousands of volts.

•High power, high frequency operation, such as that used in over-the-air television broadcasting, is better achieved in electron tubes due to improved electron mobility in a vacuum.

•Silicon transistors are much more sensitive than electron tubes to an electromagnetic pulse generated by a high-altitude nuclear explosion.Power BJT

Synthesis

• Application– Switch for a digital signal: BJT or MOSFET– Switch for a analog signal: JFET– Switch for a power signal: Power MOSFET or

BJT– Current controlled-current amplifier: BJT– Voltage controlled-current amplifier: JFET or

MOSFET• Meet current & voltage requirements• Speed: n-channel is faster than p-channel, npn

is faster thanpnp

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References

Mobile Robots: Inspiration to Implementation.Jones, Seiger & Flynn. (1999).• Introduction to Mechatronics. Histan &

Alciatore.(1999).• The Art of Electronics. Horowitz. (1980).• http://Whatis.techtarget.comhttp://Wikipedia.comPower Electronics, P. S. Bhimbhra

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Power BJT