IRF3805S

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IRF3805S MOSFET is a n-channel, silicon-gate field-effect transistor specially designed for high power switching and linear amplifying applications. In this article, the application fields and working principles of IRF3805S will be explored.

Application fields

IRF3805S features typical full-pinchoff voltage Vp of 9V, making it suitable for low voltage applications. Moreover, IRF3805S also achieves a low on-resistance of 0.03Ohm and has a very low gate charge of 6.5nC. All these characteristics make it suitable for a wide range of applications, including professional power conversion in motor drives and induction heating, solar inverters and motor control, laptop and PC AC/DC and DC/DC converters, switch mode power supplies, battery charging systems, high power LED lighting systems, Class-D amplifier and general DC/DC applications.

Working Principle

The working principle of IRF3805S lies in the extrinsic-base layer or ‘extrabase’, which is distinct from threshold voltage due to its external gate voltage effect. It is specifically designed to be used as a resistive load in power conversion applications. The IRF3805S MOSFET has an extrinsic-base layer, the gate-to-channel capacitance, and the on-state drain-to-source resistance as its primary parameters. These parameters precisely control the source-to-drain current when the device is switched on and off. The extrinsic-base layer of the device is formed when the external gate voltage applied to it is larger than the device threshold voltage.

The applied external gate voltage causes a depletion zone in the extrinsic-base layer, causing electrons to flow from the gate to the drain, which in turn creates a “virtual” source-to-drain current path. This current path is caused by the presence of the depletion zone, which acts as a resistive element thereby controlling the magnitude of the source-to-drain current. This is the basic principle on which the IRF3805S MOSFET operates.

The other important parameter, the gate-to-channel capacitance, affects the switching speed of the device. The capacitance between the gate and the drain increases as the external gate voltage is increased, thus increasing the switching speed of the device. This increased switching speed is beneficial in power applications, where speed is of utmost importance.

The on-state drain-to-source resistance, which is also known as the saturation voltage, also affects the performance of the device. The greater the resistance, the lower the saturation voltage and the lower the conduction losses resulting from it.

In conclusion, the IRF3805S MOSFET is a versatile device that can be used in a variety of applications due to its low threshold voltage, low gate charge, and low on-state resistance. Its working principle is based on the extrinsic-base layer, gate-to-channel capacitance, and on-state drain-to-source resistance. These parameters enable it to achieve high speeds of operation, low conduction losses, and improved efficiency.

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