- P Fet Reverse Protection
- P Fet Switch
- P Fet Reverse Polarity Protection
- P-fet Switch Circuit
- P Fet Symbol
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.
MOSFET is a field-effect device which requires very little power to its controlling terminal i.e. Gate to operate (switch the transistor ON or OFF). It operates by conducting only one type of carrier - either electron or hole, not both. A p channel MOSFET is just the opposite of the n channel MOSFET. The current flows from source to drain and the channel is made up of p type of charge carriers, i.e. The source in a p channel MOSFET must be at the highest potential and to completely turn it on Vgs must be negative 10 to 12 Volts. The trouble with using a high side P channel MOSFET driven from a signal that doesn't get close (less than 0.5 volts) to the high side voltage is that there is a decent probability that it will appear to be still active when you believe you have it turned off. MOSFET – Power, Single, P-Channel, SOT-23-30 V, -3.5 A Features. Low RDS(on) at Low Gate Voltage. Low Threshold Voltage. High Power and Current Handling Capability. This is a Pb−Free Device Applications. Load Switch. Optimized for Battery and Load Management Applications in Portable Equipment like Cell Phones, PDA’s. An FET is a three-terminal amplifying device. Its terminals are known as the source, gate, and drain, and correspond respectively to the emitter, base, and collector of a normal transistor. Two distinct families of FETs are in general use.
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(V
G
![Symbol Symbol](/uploads/1/3/4/8/134858974/847034558.png)
Plate 4
![Fet Fet](/uploads/1/3/4/8/134858974/298263320.png)
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.
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
How to Build a P-Channel MOSFET Switch Circuit
N-Channel MOSFET Basics
N Channel JFET Basics
P Channel JFET Basics
Types of Transistors
N-Channel MOSFET Basics
N Channel JFET Basics
P Channel JFET Basics
Types of Transistors
by Lewis Loflin
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P Fet Reverse Protection
This tutorial will explore the use of a P-channel and N-channel MOSFETs as a power switch and general transistor theory. This switch will operate on the positive side of a power supply with a negative common. This is for use with 5-volt micro controllers such as Arduino.
Pictured above is the basic electrical connections for Arduino and most modern micro-controllers. We have a negative common and a 5-volt Vcc. That dictates how we connect any driver transistor to the I/O pins. In addition each Arduino I/O pin can source/sink an absolute maximum of 40mA. (Note: operate at 20mA.)
First note that all MOSFETs are voltage operated devices and don't rely on a base current like a bipolar transistor. In many cases gate drive voltages below 5-volts won't work without a bipolar transistor switching in a higher voltage.
Update Dec. 2019. Many micro-controllers today are using 3.3-volt Vcc. This is also true of Raspberry Pi. I found two MOSFETs that work at 3.3-volts.
The IRFZ44N is an N-channel device rated at 55V and RDS(on) resistance of 0.032 Ohms max. The other is a P-channel device rated at 55V and a RDS(on) of 0.02 Ohms max.
See the following spec sheets:
Referring to Plate 1 whenever the voltage difference between the gate (G) and source (S) exceeds around 5-volts this opens a conductive channel between source (S) and drain (D) allowing current flow from the source back to the power supply. (Here we are using electron flow from negative to positive.)
This is often known as a series pass configuration.
Looking again at Plate 1 with no input to the base of Q1 the collector voltage rises to Vcc and with no difference in potential across Rgs Q6 and Q8 are turned off.
Applying 5-volts to the base resistors of Q8 and Q6 (plate 1) forward biases their base-emitter junctions allowing a small current flow Ib. Depending on the DC gain (hfe) of the individual transistors the base current is multiplied to produce Ic. The relationship is as follows:
Dropbox app osx. Ie = Ib + Ic; Ib * hfe = Ic.
The base current Ib is determined by Vin - 0.6 / Rb. The 0.6 volts is the voltage drop across the BE junction. Let's say Q1 and Q7 are 2N2222As that have minimum hfe of 90 and we desire an Ic of 20 mA. Here is how this will work:
Now some issues on switching transistors. We want them operating in their saturation mode where any additional base current will produce no increase in collector current (Ic). When making these calculations a transistor spec sheet gives a range for hfe, assume the lowest value. Next as long as we don't exceed the max base current rating assume extra current. In this case I would use a 2.2K for Rb.
When a bipolar transistor is operating at saturation the emitter-collector voltage equals 0.5V. In the case of MOSFETs Q6 and Q8 we want those operating in saturation mode as well. With a 12-volt difference between gate-source this assures a fast, hard turn on. At saturation MOSFETS such as the IRF630 and IRF9630 have a drain-source resistance of 0.4 and 0.8 ohms respectively.
So Let's find Rgs where we want to drop 11.5 volts:
P Fet Switch
Let's assume a much higher value of say 10K to assure the desired voltage drop. Again we have lots of room to play with to assure saturation of all four transistors. Note that in reality Rgs sets the current level when Q1 and Q7 are in saturation mode.
MOSFET Gate-Source Breakdown
![Symbol Symbol](/uploads/1/3/4/8/134858974/847034558.png)
One final issue is the gate-source breakdown voltage of both MOSFETs or Vgs. For the IRF630 and IRF9630 this is 20 volts. The 24-volts in Fig. A would damage Q8. The 10-volt Zener in series with Q7's collector will keep this within a safe margin.
Plate 4
Uses
There are number of advantages to the above circuits. A low source-drain turn on resistance means more power is delivered to the load and less heating of series pass MOSFETs. The ability to operate at 5-volts makes direct connections to a micro-controller a cinch. In addition this can be pulse-width-modulated to control motor speed on a say H-bridge circuit.
The largest use of these circuits is H-bridge motor controls. They are used in conjunction with N-channel MOSFET switches.
Note that Rg (or Rgs) is used to bleed the charges off the MOSFET gates or else they may not turn off.
P Fet Reverse Polarity Protection
Have fun.
P-fet Switch Circuit
I hope the series was helpful. Any corrections, suggestions etc. e-mail me at [email protected].
- Related:
- Why Your MOSFET Transistors Get Hot YouTube
- Issues on Connecting MOSFETs in Parallel YouTube
- Simple Circuits for Testing MOSFET Transistors YouTube
P Fet Symbol
- New Nov. 2014
- Using the ULN2003A Transistor Array with Arduino YouTube
- Using the TIP120 & TIP120 Darlington Transistors with Arduino YouTube
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- Using PNP Bipolar Transistors with Arduino, PIC YouTube
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