Bipolar power transistor

A power bipolar transistor (engl. Bipolar power transistor and transistor power bipolar junction , Power BJT) is a specialized version of a bipolar transistor , which is optimized for passing and blocking of large electric currents and voltages (up to several hundred amperes and up to about 1000 volts , with a component volume of approx. one cubic centimeter). In contrast to the normal bipolar transistor, the power bipolar transistor has a vertical arrangement so that the currents are evenly distributed over a large area within the semiconductor.

In industry, the power bipolar transistor - just like the power MOSFET - is an industrial standard component for influencing the electrical current. It is used as a power amplifier and switch and acts approximately like a current-controlled current source . It is increasingly being replaced by IGBT (a combination of bipolar transistor and MOSFET ).

A well-known type that is still in production today is the 2N3055 .

Structure and functionality

Schematic structure of an npn power bipolar transistor

Internal structure of a classic power transistor. The collector is electrically connected to the metal housing.

A power bipolar transistor usually has to be able to withstand a large base-collector voltage. The collector of the transistor must therefore be lightly doped so that there is no avalanche breakdown . The higher base-collector voltage results in a larger space charge zone in the base. Therefore, the base width has to set to be large, a punch (engl. Punch through ) of the transistor to be avoided. The large base width results in a much smaller current gain. Compared to small-signal bipolar transistors with current gains in the range from 100 to 1000, power bipolar transistors only have a gain of about 10-100.

In the case of a power bipolar transistor, what is known as a second breakdown can occur, which can occur with very high voltages and currents. Because of the increased temperature as a result of the high currents, the semiconductor material begins to melt.

A special design is the Darlington transistor , which consists of an emitter follower circuit of two transistors in a housing on a chip.

Parameters

• Maximum permissible collector current ( ) ${\displaystyle I_{\mathrm {C,max} }}$
• Maximum permissible collector voltage ( ) ${\displaystyle V_{\mathrm {CE,sus} }}$
• Maximum permissible transistor power loss ( ) ${\displaystyle P_{\mathrm {T} }}$

The safe operating range (engl. Safe operating area , SOA) is limited by the above parameters. It must be ensured that the maximum permissible transistor power is below a certain value so that the temperature of the semiconductor material is below the maximum value.

See also

• Basic transistor circuits
• Field effect transistor
• List of semiconductor packages