Practical transistors: JFETs | Hackade

Transistors come in a variety of flavors. The tubes used an electric field to control the current flow, and the researchers wanted to find something that works similarly without errors, such as vacuum and filament voltage. However, what they first discovered – bipolar transistors – does not work the same way. It acts as a switch using a small current to correct a larger current. What they were looking for was a FET-field effect transistor. These two come in flavors. One uses a gate separated from the channel by a thin layer of oxide (MOSFETs) and the other – a junction or JFET – uses semiconductor properties to reduce or improve the conductors in the channel. [JohnAudioTech] A recent video that you can see below takes a steady practical approach to JFET.

The concept of FETs is rather old, patents appeared in 1925 and 1934, but there was no practical device in either. William Shakley attempted and failed to create a functional FET in 1947, the same year the first point-contact transistor appeared, which was invented while trying to create a practical FET. In 1948, the bipolar junction transistor hit the scene and changed everything. Although several functional FETs were created between 1945 and 1950, the first practical devices did not appear until 1953. They had problems, so interest in technology waned when the industry focused on bipolar transistors. However, FETs have finally gotten better with bipolar technology boasting both extremely high input impedance and simplified bias.

Of course, there are flaws, so it’s important to understand the strengths and weaknesses of each technology. [John’s] The video will tell you a lot about the practical aspects of this versatile device.

We liked that in addition to some theories and graphs, he did a FET wire on a breadboard and showed things like what happens when you cool the device. A second part of the video is coming, and we’re sure it’ll be worth a look.

If you want [Bil Herd’s] Accept FET technology, we also have video. Due to their high input impedance, FET is common in things like non-contact voltage sensors, thermometers and guitar pre-amps.

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