consequently no current-limiting resistor is required in the gate input.high input impedance of the insulated gate means almost no gate current is required.In switching circuits, these FETs can be used much like bipolar junction transistors, but have some advantages: The 2N7000 has been referred to as a "FETlington" and as an "absolutely ideal hacker part." The word "FETlington" is a reference to the Darlington-transistor-like saturation characteristic.Ī typical use of these transistors is as a switch for moderate voltages and currents, including as drivers for small lamps, motors, and relays. The 2N7002 is in a TO-236 package, also known as "small outline transistor" SOT-23 surface-mount, which is the most commonly used three-lead surface-mount package. The 2N7002 is a part with similar (but not identical) electrical characteristics as the 2N7000 but different package. The BS170 can switch 500 mA, with a maximum on-resistance of 5 Ω at 10 V Vgs. Packaged in a TO-92 enclosure, both the 2N7000 and BS170 are 60 V devices. The BS250P is "a good p-channel analog of the 2N7000." The 2N7000 is a widely available and popular part, often recommended as useful and common components to have around for hobbyist use. They are sometimes listed together on the same datasheet with other variants 2N7002, VQ1000J, and VQ1000P. The 2N7000 and BS170 are two different N-channel, enhancement-mode MOSFETs used for low-power switching applications, with different lead arrangements and current ratings. The 2N7002 variant is packaged in a TO-236 surface-mount package. The BS170 has the source and drain leads interchanged. The 2N7000 is housed in a TO92 package, with lead 1 connected as the source, lead 2 as the gate, and lead 3 as the drain. The symbol doesn't always show the internal diode formed between the substrate and the source/drain/channel. Vdd is the equivalent of Vcc in a bipolar transistor circuit or the total applied voltage to the circuit.G = Gate, D = Drain, S = Source. The Vds voltage is the total applied voltage across the device from source to drain. To give a low distortion output, the Vgs voltage would be made half of the Vds voltage. The BS170 can also be used as an AC voltage amplifier. If the device is to be used as a switch, a certain amount of current will be needed to turn on a motor or other device on and an appropriate Vgs or input voltage can be calculated for that given output current. As long as Vgs is greater than Vth, we are in the saturation region, below that it's called the cutoff region. As can be seen on the graph, the Vgs voltage is gradually increased until Vth is reached, which is the threshold voltage needed to turn the device on. Depletion mode devices work the opposite way. The BS170 is an enhancement mode device, meaning it needs to be turned on or "enhanced" for current to flow through from the source to the drain. The output of the MOSFET is a low impedance, which can be as low as 1 ohm. This current is called Id or drain current. This can easily be 10 megohms or more! A current that flows through the device from source to drain and the amount that flows through it is controlled by the voltage appearing between the gate and source. This voltage is known as Vgs or the gate-source voltage. The gate sees only voltage and no current is used by it. The BS170 MOSFET is a voltage-controlled device with three terminals, gate, drain and source.
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