I've been trying to learn about transistors, but there's something that's confusing me. What are the differences between a JFET and a depletion mode MOSFET, based on how they are used? They seem very similar to each other.
JFETs (Junction Field-Effect Transistors) and depletion-mode MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are both types of field-effect transistors (FETs) and they do have some similarities in their operation. However, there are also some important differences between the two types of transistors.

The main difference between JFETs and depletion-mode MOSFETs is in how they are biased, or how the voltage is applied to the device to control the flow of current.

A JFET is a voltage-controlled device, meaning that the voltage applied to the gate terminal determines the current flow between the source and drain terminals. When a negative voltage is applied to the gate of a JFET, it creates a depletion region that restricts the flow of current between the source and drain terminals. As the gate voltage becomes more negative, the depletion region widens and the current flow is reduced.

A depletion-mode MOSFET, on the other hand, is a voltage-controlled device that operates similarly to a JFET, but it is constructed differently. In a depletion-mode MOSFET, the gate is separated from the channel by a thin layer of oxide. When a negative voltage is applied to the gate of a depletion-mode MOSFET, it attracts positive charges from the channel, creating a depletion region that restricts the flow of current between the source and drain terminals.

In terms of their practical applications, JFETs and depletion-mode MOSFETs are used in similar ways, but there are some differences. JFETs are often used in low-noise applications such as pre-amplifiers, while depletion-mode MOSFETs are used in power management applications, such as voltage regulation and switching circuits.