Enhancement mode FETs are (no), normally open and the gate usually needs its gate driven by a control circuit for it to conduct, depending on circuit details.Ī relay can also be conductive without being enabled by electrical control. To stop it from conducting, its gate must be driven beyond the voltage on its source. The depletion mode FET is normally a conductive switch, even if the gate is not driven to a voltage away from its other terminals' voltages (nc). The FET is a simple switch that have depletion mode or enhancement mode. In the two examples I list above, what would you use, and why? Other than these characteristics, I'm not sure what else might differentiate these devices. So I could see that in a more complex switching application (3P2T), or an application where you needed a lot of switches, an analog switch IC would make sense because of its compactness and simplicity. They also have both a NO and an NC output, whereas an FET, by itself, is either NO or NC, but not both. That is basically all I know about them.Īnalog switch ICs come in a wide variety of designs, with multiple switches and multi-pole/multi-throw configurations. The relays I have seen also seem to have slower switching speed than the other two: the solid state relays seem to have switching speeds in the ms, where the others have switching speeds in the tens of ns.įETs are, in a simple sense, like a SPST switch. They are usually larger and more expensive than ICs. They can be designed such that there is a very large difference in voltage between the control circuit and the switched circuit. Relays, especially mechanical relays like the solenoid in your car, excel at switching large currents. But I would like to have a broader understanding of when the use of each of these types of devices is appropriate.
#Fet transistor as a switch manual
The two specific applications I'm considering are 1) replacing a manual NO switch in a device with a switch that is controlled by the Arduino, and 2) feeding a PWM input to a switch to cause a parallel resistor to cycle in and out of circuit, thereby approximating a digital pot via the PWM duty cycle. Frankly, I'm a little overwhelmed, and I wonder if anybody could help me understand what qualities differentiate these devices, that would cause someone to choose one of them over another.
A spokesman claimed that "it may have far-reaching significance in electronics and electrical communication." Despite its delicate mechanical construction, many thousands of units were produced in a metal cartridge package as the Bell Labs "Type A" transistor.I have been thinking about switching, and I have come up with at least three ways to accomplish switching: with an FET, with an analog switch IC, and with a relay. Named the "transistor" by electrical engineer John Pierce, Bell Labs publicly announced the revolutionary solid-state device at a press conference in New York on June 30, 1948. On December 23 they demonstrated their device to lab officials - in what Shockley deemed "a magnificent Christmas present." The voltage on one contact modulated the current flowing through the other, amplifying the input signal up to 100 times. Bardeen and Brattain applied two closely-spaced gold contacts held in place by a plastic wedge to the surface of a small slab of high-purity germanium. On December 16, 1947, their research culminated in the first successful semiconductor amplifier. With experimental physicist Walter Brattain, Bardeen began researching the behavior of these "surface states." A year later theoretical physicist John Bardeen suggested that electrons on the semiconductor surface might be blocking penetration of electric fields into the material, negating any effects. That April he conceived a "field-effect" amplifier and switch based on the germanium and silicon technology developed during the war, but it failed to work as intended. Among other things, this group pursued research on semiconductor replacements for unreliable vacuum tubes and electromechanical switches then used in the Bell Telephone System.
Encouraged by Executive Vice President Mervin Kelly, William Shockley returned from wartime assignments in early 1945 to begin organizing a solid-state physics group at Bell Labs.
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