VRF191

Series:	--
Packaging:	Bulk
Part Status:	Obsolete
Transistor Type:	N-Channel
Frequency:	30MHz
Gain:	22dB
Voltage - Test:	100V
Current Rating:	12A
Noise Figure:	--
Current - Test:	250mA
Power - Output:	150W
Voltage - Rated:	270V
Package / Case:	T11
Supplier Device Package:	T11

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VRF191 is a two-terminal field effect transistor (FET) from Fairchild Semiconductor. It is in a Class C enhancement-mode FET, having a relatively low maximum drain current (about 100 mA) and a maximum voltage rating of 30V. It is primarily used in RF applications in the very high frequency range (VHF) and ultra-high frequency range (UHF), due to its ability to provide gain. It is widely used in radio transmitters and transceivers, as well as antenna tuning, impedance matching, and filter applications.

Working principles of FETs are different compared to BJTs, as FETs are voltage-controlled devices rather than current-controlled devices. In this type of transistor, the gate-to-source voltage controls the conductivity or channel width between the drain and the source. In other words, an increase in the gate voltage causes an increase in the current flowing through the channel. To understand the VRF191’s working principles, it’s important to remember that it is in the enhancement mode. This means that it needs a positive gate-to-source voltage in order to “turn on” the channel, and thus allow current to flow from the drain to the source.

In the off-state (or cut-off state), the gate-to-source voltage is zero, meaning that no current can flow through the channel between the drain and the source. In this state, the VRF191 can be said to be acting like an open switch—a conductive path between drain and source is not established. To turn the VRF191 “on”, a positive voltage must be applied to the gate. This causes electrons to be attracted to the gate and—in turn—to the drain, thus creating a conductive path between the two terminals. This path is very narrow, as the width of the “conductive channel” is dependent on the magnitude of the gate voltage. This is why the VRF191 is known as a “high impedance” FET.

The VRF191 also has a relatively high transconductance and is therefore quite sensitive to the magnitude of the gate voltage. It is a low-noise device and has very low input and output capacitances. It also exhibits low reverse current, making it ideal for RF applications where noise and signal conformance is important.

The VRF191’s working principle also makes it useful in RF antenna tuning applications. By varying the gate voltage, the impedance of the antenna can be adjusted to match the feeder line and thus optimize the performance of the antenna. Similarly, the VRF191 can be used in filter and impedance matching circuits, to improve the overall performance of the system.

In summary, the VRF191 is a two-terminal field effect transistor primarily used in RF applications due to its high impedance, low noise, and high transconductance. It is useful in radio transmitters and receivers, antenna tuning, and filter applications. Its working principle, which is based on the ability to vary the conductivity of the channel between the drain and source by varying the gate voltage, allows it to be used in various applications to improve the performance of a system.

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