FDB8444

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The FDB8444 is a high voltage, enhancement-type field effect transistor (FET) manufactured by Fairchild Semiconductor. It is capable of dissipating a peak pulse drain current (I DM) of 11A, and continuous drain current (I D) of 4.7A. It is widely used in audio and video amplifier stages, motor control circuits, and power switch circuits. This article examines the application field and working principle of the FDB8444.

Application Field

The FDB8444 is well-suited for a variety of applications, such as high voltage switching, audio/video amplifiers, motor control, and power switch circuits. As a high voltage switch, the FDB8444 can be used to driving loads up to 250 V (V DS) with a maximum gate-source voltage (V GS) of 25 V and a maximum operating temperature of 175 °C. In audio and video amplifiers, the FDB8444 can be used to drive large capacitive loads without distortion. In motor control circuits, the FDB8444 is capable of handling high current and voltage levels, making it suitable for a wide range of variable speed applications. Finally, the FDB8444 can be used in power switch circuits, allowing for a high current on/off control.

Working Principle

The FDB8444 is an enhancement-type FET, which means it is an insulated gate device that is designed to be in an off state when zero volts is applied between the gate and source (V GS = 0V). When a positive charge is applied to the gate of the FET, it increases the electric field between the gate and the drain, allowing a linear current flow between the drain and the source (V GS > 0V). The amount of current that flows through the FET is controlled by the voltage applied to the gate (V GS ).

The mobility of the majority carriers (holes or electrons) between the source and the channel is controlled by the vertical electric field established between the gate and the source (V GS ). When the majority carriers move to the channel region, a conducting channel is formed and the transistor can turn on. The FDB8444 has a P-channel structure, meaning that the majority carriers are holes and the channel is formed when the gate voltage is made more positive than the source voltage (V GS > 0V).

The drain current (I D ) of the FDB8444 is affected by the sizes of both the drain and source regions. The drain region is typically made larger than the source region, which increases the current gain when the device is turned on. The I D -V DS (drain-source voltage) characteristic can be described using a nearly constant transconductance when operated in a linear region. The drain current (I D ) of the FET is also affected by the temperature, and it increases by approximately 0.25% for every 1 °C rise in temperature.

Conclusion

The FDB8444 is an enhancement-type FET manufactured by Fairchild Semiconductor, capable of dissipating a peak pulse drain current of 11A, and continuous drain current of 4.7A. It is suitable for a variety of applications, such as high voltage switching, audio/video amplifiers, motor control, and power switch circuits. The working principle of the FDB8444 is based on controlling the mobility of the majority carriers between the source and the channel, by the vertical electric field established between the gate and the source. The drain current of the FET is affected by the sizes of both the drain and source regions, as well as the temperature.

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