Category: Education
-
6.2 Depletion-type IGFETs
Insulated gate field-effect transistors are unipolar devices just like JFETs: that is, the controlled current does not have to cross a PN junction. There is a PN junction inside the transistor, but its only purpose is to provide that nonconducting depletion region which is used to restrict current through the channel. Schematic Symbol and Physical…
-
6.1 Introduction to Insulated-gate Field-effect Transistors
As was stated in the last chapter, there is more than one type of field-effect transistor. The junction field-effect transistor, or JFET, uses voltage applied across a reverse-biased PN junction to control the width of that junction’s depletion region, which then controls the conductivity of a semiconductor channel through which the controlled current moves. Another…
-
5.4 Active-mode Operation (JFET)
JFETs, like bipolar transistors, are able to “throttle” current in a mode between cutoff and saturation called the active mode. To better understand JFET operation, let’s set up a SPICE simulation similar to the one used to explore basic bipolar transistor function: Spice Simulation of a JFET Operation jfet simulation vin 0 1 dc 1…
-
5.3 Meter Check of a Transistor (JFET)
Testing a JFET with a multimeter might seem to be a relatively easy task, seeing as how it has only one PN junction to test: either measured between gate and source, or between gate and drain. Testing Continuity of an N-channel JFET Testing continuity through the drain-source channel is another matter, though. Remember from the…
-
5.2 The Junction Field-effect Transistor (JFET) as a Switch
Like its bipolar cousin, the field-effect transistor may be used as an on/off switch controlling electrical power to a load. Let’s begin our investigation of the JFET as a switch with our familiar switch/lamp circuit: Remembering that the controlled current in a JFET flows between source and drain, we substitute the source and drain connections…
-
5.1 Introduction to Junction Field-effect Transistors (JFET)
A transistor is a linear semiconductor device that controls current with the application of a lower-power electrical signal. Transistors may be roughly grouped into two major divisions: bipolar and field-effect. In the last chapter, we studied bipolar transistors, which utilize a small current to control a large current. In this chapter, we’ll introduce the general…