A constant-current diode is an electronic device that limits current to a maximal specified value for the device. It is known as a current-limiting diode (CLD) or current-regulating diode (CRD).
It consists of an n-channel JFET with the gate shorted to the source, which functions like a two-terminal current limiter or current source (analogous to a voltage-limiting Zener diode). It allows a current through it to rise to a certain value, and then level off at a specific value. Unlike Zener diodes, these diodes keep the current constant instead of the voltage constant. These devices keep the current flowing through them unchanged when the voltage changes.
On the similarities side, MOSFETs and JFETs are both voltage-controlled transistors. A voltage at the gate terminal of the transistor either turns the transistor on or off. They are unlike BJTs, which are current-controlled. MOSFETs and JFETs also both have small transconductance (gain) values when compared to bipolar junction transistors. P-Channel MOSFET Basics. A P-Channel MOSFET is a type of MOSFET in which the channel of the MOSFET is composed of a majority of holes as current carriers. When the MOSFET is activated and is on, the majority of the current flowing are holes moving through the channels.
Note that some devices are unidirectional and voltage across the device must have only one polarity for it to operate as a CLD, whereas other devices are bidirectional and can operate properly in either polarity.
- MOSFET stands for Metal Oxide Silicon Field Effect Transistor or Metal Oxide Semiconductor Field Effect Transistor. This is also called as IGFET meaning Insulated Gate Field Effect Transistor. The FET is operated in both depletion and enhancement modes of operation. The following figure shows how a practical MOSFET looks like.
- Junction Field Effect Transistor (JFET) The Junction Field Effect transistor (JFET) is one of the types of FET transistors. JFET is a simplest form of FET transistors and it has three terminals. The JFET transistors are used as electronically controlled switches, Voltage controlled resistors and as amplifiers.
Wide-bandgap materials such as silicon carbide have been used in production devices to enable high-voltage applications in the kilovolt range.[1]
The 2N4392 JFET is designed to be operated as a switch, and its transfer characteristic is far from ideal. Finally, find the complete output characteristic for your JFET with the JFET Output Tracer option. Take scans in both the linear and saturated regimes. Save this JFET for many of the remaining exercises. Curve Tracer information.
References[edit]
- ^'CALY Technologies SiC CLD devices'. CALY Technologies. Retrieved 26 April 2020.
External links[edit]
- Advantages of Constant Current Regulators (CCR) in Driving LEDs on YouTube
- Diode
- CLD diode datasheet, MCC
- CRD diode datasheet, Semitec
- J500 diode datasheet, Linear Systems / Siliconix / Vishay
- 1N5283 to 1N5314 diode datasheet, Central Semiconductor
- JFET
- 2N5457/8/9 & MMBF5457/8/9 JFET datasheet, ON Semiconductor (Former Fairchild)
A P-Channel MOSFET is a type of MOSFET in which the channel of the MOSFET is composed of a majority of holes as current carriers. When the MOSFET is activated and is on, the majority of the current flowing are holes moving through the channels.
This is in contrast to the other type of MOSFET, which are N-Channel MOSFETs, in which the majority ofcurrent carriers are electrons.
Before, we go over the construction of P-Channel MOSFETs, we must go over the 2 types that exist. There are 2 types of P-Channel MOSFETs, enhancement-type MOSFETs and depletion-type MOSFETs.
A depletion-type MOSFET is normally on (maximum current flows from source to drain) when no differencein voltage exists between the gate and source terminals. However, if a voltage is applied to its gate lead, the drain-source channel becomes more resistive, until the gate voltage is so high, the transistor completely shuts off. An enhancement-type MOSFET is the opposite. It is normally off when the gate-source voltage is 0V(VGS=0). However, if a voltage is applied to its gate lead, the drain-source channel becomesless resistive.
In this article, we will go over how both P-Channel enhancement-type and depletion-type MOSFETs are constructed and operate.
How P-Channel MOSFETs Are Constructed Internally
An P-Channel MOSFET is made up of a P channel, which is a channel composed of a majority of hole current carriers. The gate terminals are made up of N-type material.
Depending on the voltage quantity and type (negative or positive)determines how the transistor operates and whether it turns on or off.
How a P-Channel Enhancement-type MOSFET Works
How to Turn on a P-Channel Enhancement Type MOSFET
To turn on a P-Channel Enhancement-type MOSFET, apply a positive voltage VS to the source of the MOSFET and apply a negative voltage to the gate terminal of the MOSFET (the gate must be sufficiently more negative than the threshold voltage across the drain-source region(VG
So with a sufficient positive voltage, VS, to the source and load, and sufficient negative voltage applied to the gate, the P-Channel Enhancement-type MOSFET is fully functional and is in the active 'ON' mode of operation.
How to Turn Off a P-Channel Enhancement Type MOSFET
To turn off a P-channel enhancement type MOSFET, there are 2 steps you can take. You can either cut off the bias positive voltage, VS, that powers the source. Or you can turn off the negative voltagegoing to the gate of the transistor.
How a P-Channel Depletion-type MOSFET Works
How to Turn on a P-Channel Depletion Type MOSFET
To turn on a P-Channel Depletion-Type MOSFET, for maximum operation, the gate voltage feeding the gate terminal should be 0V. With the gate voltage being 0V, the drain current is at is largest value and the transistor is in the active 'ON'region of conduction.
Jfet And Mosfet Difference
So, again, to turn on a P channel depletion-type MOSFET, positive voltage is applied to the source of the p-channel MOSFET. So we power the source terminal of the MOSFET with VS, a positive voltage supply. With a sufficient positive voltage, VS, and no voltage (0V) applied to the base, the P-channel Depletion-type MOSFET is in maximum operation and has the largest current.
How to Turn Off a P-Channel Depletion Type MOSFET
To turn off a P-channel MOSFET, there are 2 steps you can take. You can either cut off the bias positivevoltage, VDD, that powers the drain. Or you can apply a negative voltage to the gate. When a negativevoltage is applied to the gate, the current is reduced. As the gate voltage, VG, becomes more negative, the current lessens until cutoff, which is when then MOSFET is in the 'OFF' condition. This stops a large source-drain current.
So ,again, as negative voltage is applied to the gate terminal of the P channel depletion-type MOSFET, the MOSFET conducts less and less current across the source-drain terminal. When the gate voltage reaches a certain negative voltage threshold, it shuts the transistor off. Negative voltage shuts the transistor off. This is for a depletion-type P-channel MOSFET.
MOSFET transistors are used for both switching and amplifying applications. MOSFETs are perhaps the most popular transistors used today. Their high input impedance makes them draw very little input current, they are easy to make, can be made very small, and consume very little power.
Related Resources
What Is Jfet Mosfet
How to Build a P-Channel MOSFET Switch Circuit
N-Channel MOSFET Basics
N Channel JFET Basics
P Channel JFET Basics
Types of Transistors
Jfet Mosfet Symbol