Mosfet 5v

A MOSFET is classified as Logic Level MOSFET if it gets fully turned on with Vgs in the range of 3 to 5 volts. If you use a 5V Arduino board, then all Logic Level MOSFETs should be OK. If you are using a 3.3V board, then you have to check that the MOSFET you are using is compatible with 3.3V switching. Apr 15, 2021 When a Logic 1 (assuming a 5V Microcontroller, Logic 1 is 5V and Logic 0 is 0V) is supplied to the gate of the MOSFET, it turns ON and allows drain current to flow. As a result, the LED is turned ON. Similarly, when a Logic 0 is given to the gate of the MOSFET, it turns OFF and in turn switches OFF the LED. MOSFET MOSFT 5.0A 29mOhm 30V 2.5V drv capable Enlarge Mfr. Part # IRLML6344TRPBF. Mouser Part # 942-IRLML6344TRPBF. Infineon / IR: MOSFET MOSFT 5.0A 29mOhm 30V 2.5V.

1. P-Channel MOSFET Tutorial With Only Positive Voltages
2. N-channel Mosfet Turn Constantly On After A While | All ..
3. Mosfet For 3.3v Logic

The interfacing of power devices like BJTs, and MOSFETs with Arduino output is a crucial configuration which allows switching high power loads through low power outputs of an Arduino.

In this article we elaborately discuss the correct methods of using or connecting transistors like BJTs and mosfets with any microcontroller or an Arduino.

Such stages are also referred to as 'Level Shifter' because this stage changes the voltage level from a lower point to a higher point for the relevant output parameter. For example here the level shift is being implemented from Arduino 5V output to MOSFET 12V output for the selected 12V load.

No matter how well programmed or coded your Arduino may be, if it's not correctly integrated with a transistor or an external hardware, could result in inefficient operation of the system or even damage to the components involved in the system.

Therefore, it becomes extremely important to understand and learn the right methods of using external active components like mosfets and BJTs with a microcontroller, so that the final outcome is effective, smooth and efficient.

Before we discuss the interfacing methods of transistors with Arduino, it would be useful to learn the basic characteristics and working of BJTs and mosfets.

Electrical Characteristics of Transistors (Bipolar)

BJT stands for bipolar junction transistor.

The basic function of a BJT is to switch ON an attached load in response to an external voltage trigger. The load is supposed to be mostly heavier in current compared to the input trigger.

Thus, the basic function of a BJT is to switch ON a higher current load in response to a lower current input trigger.

Technically, this is also called biasing of the transistor, which means using current and voltage to operate a transistor for an intended function, and this biasing has to be done in the most optimal way.

BJTs have 3 leads or 3 pins, namely base, emitter, collector.

The base pin is used for feeding the external input trigger, in the form of small voltage and current.

The emitter pin is always connected to the ground or the negative supply line.

The collector pin is connected to the load via the positive supply.

BJTs can be found with two types of polarities, NPN and PNP. The basic pin configuration is the same for both NPN and PNP as explained above, except the DC supply polarity which becomes just the opposite.

The pinouts of a BJT could be understood through the following image:

In the image above we can see the basic pinout configuration of an NPN and an PNP transistors (BJTs). For the NPN the emitter becomes the ground line, and is connected with the negative supply.

Normally when the word 'ground' is used in a DC circuit, we assume it to be the negative supply line.
However, for a transistor the ground line associated with the emitter is with reference to its base and the collector voltages, and the emitter 'ground' may not necessarily mean the negative supply line.

Yes, for an NPN BJT the ground could be the negative supply line, but for an PNP transistor the 'ground' is always referenced to the positive supply line, as shown in the figure above.

The switching ON/OFF function of both the BJTs is basically the same, but the polarity changes.

Since the emitter of a BJT is the 'exit' passage for the current entering through and base and the collector, it has to be 'grounded' to a supply line which should be opposite to the voltage used at base/collector inputs. Otherwise the circuit won't complete.

For a NPN BJT, the base and the collector inputs are associated with a positive trigger or switching voltage, therefore the emitter must be referenced to the negative line.

This ensures that the positive voltages entering the base and collector are able to reach the negative line through the emitter and complete the circuit.

For a PNP BJT, the base and the collector are associated with a negative voltage input, therefore naturally the emitter of a PNP must be referenced to the positive line, so that the positive supply can enter through the emitter and finish its journey from the base and the collector pins.

Note that the flow of current for the NPN is from base/collector towards emitter, while for the PNP, it's from the emitter towards the base/collector.

In both the cases, the objective is to switch ON the collector load through a small voltage input at the base of the BJT, only the polarity changes that's all.

The following simulation shows the basic operation:

In the simulation above, as soon as the button is pressed, the external voltage input enters the base of the BJT and reaches the ground line via the emitter.

While this happens the collector/emitter passage inside the BJT opens up, and allows the positive supply from top to enter the bulb, and pass through the emitter to ground, switching ON the bulb (load).

Both the switching happen almost simultaneously in response to the pressing of the push button.

The emitter pin here becomes the common 'exit' pinout for both the input feeds (base and collector).

And the emitter supply line becomes the common ground line for the input supply trigger, and also the load.

Which means that, the supply line connecting with the BJT emitter must be also strictly connected with the ground of the external trigger source, and the load.

Why we use a Resistor at the Base of a BJT

The base of a BJT is designed to work with low power inputs, and this pin cannot take in large current inputs, and therefore we employ a resistor, just to make sure that no large current is allowed to enter the base.

P-Channel MOSFET Tutorial With Only Positive Voltages

The basic function of the resistor is to limit current to a correct specified value, as per the load specification.

Please Note that, for BJTs this resistor must be dimensioned as per the collector side load current.

Why?

Because BJTs are current dependent 'switches'.

Meaning, the base current needs to be increased or decreased or adjusted in accordance with the load current specs at the collector side.

But the switching voltage required at the base of a BJT can be as low as 0.6V or 0.7V. Meaning, BJT collector load could be switched ON with a voltage as low as 1V across base/emitter of a BJT.
Here's the basic formula for calculating the base resistor:

R = (Us - 0.6)Hfe / Load Current,

Where R = base resistor of the transistor,

Us = Source or the trigger voltage to the base resistor,

Hfe = Forward current gain of the transistor (can be found from the datasheet of the BJT).

Although the formula looks neat, it is not absolutely necessary always to configure the base resistor so accurately.

It is simply because, the BJT base specifications has a wide tolerance range, and can easily tolerate wide differences in the resistor values.

For example, to connect a relay having a 30mA coil resistance, the formula may roughly provide a resistor value of 56K for a BC547 at 12V supply input..but I normally prefer using 10K, and it works flawlessly.

However, if you are not following the optimal rules there could be something not good with the results, right?

Technically that makes sense, but again the lose is so small compared to the effort spent for the calculations, it can be neglected.

For example using 10K instead of 56K may force the transistor to work with a slightly more base current, causing it to warm up slightly more, may be a couple degrees higher.. which doesn't matter at all.

How to Connect BJT with Arduino

OK, now let's come to the actual point.

Since we have so far comprehensively learned regarding how a BJT needs to be biased and configured across its 3 pinouts, we can quickly grasp the details regarding its interfacing with any microcontroller such as Arduino.

The main purpose of connecting a BJT with an Arduino is usually to switch ON a load or some parameter at the collector side, in response to a programmed output from one of the Arduino output pins.

Here, the trigger input for the BJT base pin is supposed to come from the Arduino. This implies the end of the base resistor simply needs to be attached with the relevant output from the Arduino, and the collector of the BJT with the load or any intended external parameter.

Update to the latest mac os. Since a BJT requires hardly 0.7V to 1V for an effective switching, 5V from the Arduino output pin becomes perfectly adequate for driving a BJT and operating reasonable loads.
An example configuration can be see the following image:

In this image we can see how a programmed Arduino is used for operating a small load in the form of relay via BJT driver stage. The relay coil becomes the collector load, while the signal from the selected Arduino output pin acts like the input switching signal for the BJT base.

Although, a relay becomes the best option for operating heavy loads via a transistor driver, when mechanical switching becomes an undesirable factor, upgrading BJTs becomes a better choice for operating high current DC loads, as shown below.

In the above example a Darlington transistor network can be seen, configured for handling the indicated high current 100 watt load without depending on a relay. This allows seamless switching of the LED with minimum disturbance, ensuring a long working life for all the parameters.

Now let's proceed further, and see how mosfets can be configured with an Arduino

Electrical Characteristics of MOSFET

N-channel Mosfet Turn Constantly On After A While | All ..

The purpose of using a mosfet with an Arduino is usually similar to that of BJT as discussed above.

However, since normally MOSFETs are designed to handle higher current specs efficiently compared to BJTs, these are mostly used for switching high power loads.

Before we comprehend the interfacing of a mosfet with Arduino it would interesting to know the basic difference between BJTs and mosfets

In our previous discussion, we understood that BJTs are current dependent devices, because their base switching current is dependent on the collector load current. Higher load currents will demand higher base current, and vice versa.

For mosfets this is not true, in other words mosfets gate which is equivalent to BJT base, require minimal current to switch ON, regardless of the drain current (drain pin of mosfet is equivalent to collector pin of BJT).

Having said this, although the current is not the deciding factor for switching a mosfet gate, voltage is.

Therefore mosfets are considered as voltage dependent devices

The minimum voltage required for creating healthy biasing for a mosfet is 5V or 9V, 12v being the most optimal range for switching ON a mosfet fully.

Therefore we can assume that in order to switch ON a mosfet, and a load across its drain, a 10V supply can be used across its gate for an optimal outcome.

Equivalent pins of Mosfets and BJTs

The following image shows the complementing pins of mosfets and BJTs.

Base corresponds to Gate-Collector corresponds to Drain-Emitter corresponds to Source.

What Resistor should be Used for a Mosfet Gate

From our earlier tutorials we understood that the resistor at base of a BJT is crucial, without which the BJT can instantly get damaged.

For a MOSFET this may not be so relevant, because MOSFETs are not affected with current differences at their gates, instead a higher voltage could be considered dangerous. Typically anything above 20V can be bad for a MOSFET gate, but current may be immaterial.

Update mac to os x 10.11. Due to this, a resistor at the gate is not relevant since resistors are used for limiting current, and mosfet gate is not dependent on current.

That said, MOSFETs are hugely vulnerable to sudden spikes and transients at their gates, compared to BJTs.

For this reason a low value resistor is generally preferred at the gates of MOSFETs, just to ensure no sudden voltage spike is able to go through the MOSFET gate and tear it apart internally.

Typically any resistor between 10 and 50 ohms could be used at MOSFET gates for safeguarding their gates from unexpected voltage spikes.

Interfacing a MOSFET with Arduino

As explained in the above paragraph, a mosfet will need around 10V to 12V for properly switching ON, but since Arduinos work with 5V its output cannot be directly configured with a mosfet.

Since an Arduino runs with 5V supply, and all of its outputs are designed to produce 5V as the logic high supply signal. Although this 5V may have the ability to switch ON a MOSFET, it may result in an inefficient switching of the devices and heating up issues.

For effective MOSFET switching, and to transform the 5V output from Arduino into a 12V signal, an intermediate buffer stage could be configured as shown in the following image:

In the figure, the MOSFET can be seen configured with a couple of BJT buffer stages which allows the MOSFET to use the 12V from the power supply and switch ON itself and the load effectively.

Two BJTs are used here since a single BJT would cause the MOSFET to conduct oppositely in response to every positive Arduino signals.

Suppose one BJT is used, then the while the BJT is ON with a positive Arduino signal, the mosfet would be switched Off, since its gate would be grounded by the BJT collector, and the load would be switched ON while the Arduino is OFF.

Basically, one BJT would invert the Arduino signal for the mosfet gate resulting in an opposite switching response.

To correct this situation, two BJTs are used, so that the second BJT inverts the response back and allows the mosfet to switch ON for every positive signals only from the Arduino.

Mosfet For 3.3v Logic

Final Thoughts

By now you should have comprehensively understood the correct method of connecting BJTs and mosfets with a microcontroller or an Arduino.

You might have noticed that we have mostly used NPN BJTs and N-channel mosfets for the integrations, and have avoided using the PNP and P-channel devices. This is because NPN versions work ideally like a switch and is easy to comprehend while configuring.

It's like driving a car normally in the forward direction, rather than looking behind and driving it in the reverse gear. In both ways the car would operate and move, but driving in the reverse gear is much inefficient and doesn't make sense. The same analogy applies here, and using NPN or N-channel devices become a better preference compared to PNP or P-channel mosfets.

If you have any doubts, or if you think I may have missed something here, please use the comment box below for further discussion.

In this tutorial, we will have a brief introduction to MOSFET i.e., the Metal Oxide Semiconductor Field Effect Transistor. We will learn about different types of MOSFET (Enhancement and Depletion), its internal structure, an example circuit using MOSFET as a Switch and a few common applications.

Introduction

Transistors, the invention that changed the World. They are semiconductor devices that act as either an electrically controlled switch or a signal amplifier. Transistors come a variety of shapes, sizes and designs but essentially, all transistors fall under two major families. They are:

• Bipolar Junction Transistors or BJT
• Field Effect Transistors or FET

To learn more about a basics of transistor and its history, read the Introduction to Transistors tutorial.

There are two main differences between BJT and FET. The first difference is that in BJT, both the majority and minority charge carriers are responsible for current conduction whereas in FETs, only the majority charge carriers are involved.

The other and very important difference is that a BJT is essentially a current controlled device meaning the current at the base of the transistor determines the amount of current flowing between collector and emitter. In case of a FET, the voltage at the Gate (a terminal in FET equivalent to Base in BJT) determines the current flow between the other two terminals.

FETs are again divided into two types:

• Junction Field Effect Transistor or JFET
• Metal Oxide Semiconductor Field Effect Transistor or MOSFET

Let us focus on MOSFET in this tutorial.

Metal Oxide Semiconductor FET

The Metal Oxide Semiconductor Field Effect Transistor (MOSFET) is one type of FET transistor. In these transistors, the gate terminal is electrically insulated from the current carrying channel so that it is also called as Insulated Gate FET (IG-FET). Due to the insulation between gate and source terminals, the input resistance of MOSFET may be very high such (usually in the order of 1014 ohms.

Like JFET, the MOSFET also acts as a voltage controlled resistor when no current flows into the gate terminal. The small voltage at the gate terminal controls the current flow through the channel between the source and drain terminals. In present days, the MOSFET transistors are mostly used in the electronic circuit applications instead of the JFET.

MOSFETs also have three terminals, namely Drain (D), Source (S) and Gate (G) and also one more (optional) terminal called substrate or Body (B). MOSFETs are also available in both types, N-channel (NMOS) and P-channel (PMOS). MOSFETs are basically classified in to two forms. They are:

• Depletion Type
• Enhancement Type

Depletion Type

The depletion type MOSFET transistor is equivalent to a “normally closed” switch. The depletion type of transistors requires gate – source voltage (V_GS) to switch OFF the device.

The symbols for depletion mode of MOSFETs in both N-channel and P-channel types are shown above. In the above symbols, we can observe that the fourth terminal (substrate) is connected to the ground, but in discrete MOSFETs it is connected to source terminal. The continuous thick line connected between the drain and source terminal represents the depletion type. The arrow symbol indicates the type of channel, such as N-channel or P-channel.

In this type of MOSFETs a thin layer of silicon is deposited below the gate terminal. The depletion mode MOSFET transistors are generally ON at zero gate-source voltage (VGS). The conductivity of the channel in depletion MOSFETs is less compared to the enhancement type of MOSFETs.

Enhancement Type

The Enhancement mode MOSFET is equivalent to “Normally Open” switch and these types of transistors require a gate-source voltage to switch ON the device. The symbols of both N-channel and P-channel enhancement mode MOSFETs are shown below.

Here, we can observe that a broken line is connected between the source and drain, which represents the enhancement mode type. In enhancement mode MOSFETs, the conductivity increases by increasing the oxide layer, which adds the carriers to the channel.

Generally, this oxide layer is called as ‘Inversion layer’. The channel is formed between the drain and source in the opposite type to the substrate, such as N-channel is made with a P-type substrate and P-channel is made with an N-type substrate. The conductivity of the channel due to electrons or holes depends on N-type or P-type channel respectively.

Structure of MOSFET

Here, we can observe that the gate terminal is situated on top of thin metal oxide insulated layer and two N-type regions are used below the drain and source terminals.

In the above MOSFET structure, the channel between drain and source is an N-type, which is formed opposite to the P-type substrate. It is easy to bias the MOSFET gate terminal for the polarities of either positive (+ve) or negative (-ve).

If there is no bias at the gate terminal, then the MOSFET is generally in non-conducting state so that these MOSFETs are used to make switches and logic gates. Both the depletion and enhancement modes of MOSFETs are available in N-channel and P-channel types.

Depletion Mode

The depletion mode MOSFETs are generally known as ‘Switched ON’ devices, because these transistors are generally closed when there is no bias voltage at the gate terminal. If the gate voltage increases in positive, then the channel width increases in depletion mode.

As a result the drain current I_D through the channel increases. If the applied gate voltage more negative, then the channel width is very less and MOSFET may enter into the cutoff region. The depletion mode MOSFET is a rarely used type of transistor in the electronic circuits.

The following graph shows the Characteristic Curve of Depletion Mode MOSFET.

The V-I characteristics of the depletion mode MOSFET transistor are given above. This characteristic mainly gives the relationship between drain- source voltage (V_DS) and drain current (I_D). The small voltage at the gate controls the current flow through the channel.

The channel between drain and source acts as a good conductor with zero bias voltage at gate terminal. The channel width and drain current increases if the gate voltage is positive and these two (channel width and drain current) decreases if the gate voltage is negative.

Enhancement Mode

The Enhancement mode MOSFET is commonly used type of transistor. This type of MOSFET is equivalent to normally-open switch because it does not conduct when the gate voltage is zero. If the positive voltage (+V_GS) is applied to the N-channel gate terminal, then the channel conducts and the drain current flows through the channel.

If this bias voltage increases to more positive then channel width and drain current through the channel increases to some more. But if the bias voltage is zero or negative (-V_GS) then the transistor may switch OFF and the channel is in non-conductive state. So now we can say that the gate voltage of enhancement mode MOSFET enhances the channel.

Enhancement mode MOSFET transistors are mostly used as switches in electronic circuits because of their low ON resistance and high OFF resistance and also because of their high gate resistance. These transistors are used to make logic gates and in power switching circuits, such as CMOS gates, which have both NMOS and PMOS Transistors.

The V-I characteristics of enhancement mode MOSFET are shown above which gives the relationship between the drain current (ID) and the drain-source voltage (VDS). From the above figure we observed the behavior of an enhancement MOSFET in different regions, such as ohmic, saturation and cut-off regions.

MOSFET transistors are made with different semiconductor materials. These MOSFETs have the ability to operate in both conductive and non-conductive modes depending on the bias voltage at the input. This ability of MOSFET makes it to use in switching and amplification.

N-Channel MOSFET Amplifier

When compared to BJTs, MOSFETs have very low transconductance, which means the voltage gain will not be large. Hence, MOSFETs (for that matter, all FETs) are generally not used in amplifier circuits.

But, none the less, let us see a single-stage ‘class A’ amplifier circuit using N-Channel Enhancement MOSFET. The N-channel enhancement mode MOSFET with common source configuration is the mainly used type of amplifier circuit than others. The depletion mode MOSFET amplifiers are very similar to the JFET amplifiers.

The input resistance of the MOSFET is controlled by the gate bias resistance which is generated by the input resistors. The output signal of this amplifier circuit is inverted because when the gate voltage (V_G) is high the transistor is switched ON and when the voltage (V_G) is low then the transistor is switched OFF.

The general MOSFET amplifier with common source configuration is shown above. This is an amplifier of class A mode. Here the voltage divider network is formed by the input resistors R1 and R2 and the input resistance for the AC signal is given as Rin = RG = 1MΩ.

The equations to calculate the gate voltage and drain current for the above amplifier circuit are given below.

V_G = (R₂ / (R₁ + R₂))*VDD

I_D = V_S/ R_S

Where,

V_G = gate voltage

V_S = input source voltage

V_DD = supply voltage at drain

R_S = source resistance

R₁ & R₂ = input resistors

The different regions in which the MOSFET operates in their total operation are discussed below.

Cut-off Region: If the gate-source voltage is less than the threshold voltage then we say that the transistor is operating in the cut-off region (i.e. fully OFF). In this region drain current is zero and the transistor acts as an open circuit.

V_GS < V_TH => I_DS = 0

Ohmic (Linear) Region: If the gate voltage is greater than threshold voltage and the drain-source voltage lies between VTH and (VGS – VTH) then we say that the transistor is in linear region and at this state the transistor acts as a variable resistor.

V_GS > V_TH and V_TH < V_DS < (V_GSVGS – V_TH) => MOSFET acts as a variable Resistor

Saturation Region: In this region the gate voltage is much greater than threshold voltage and the drain current is at its maximum value and the transistor is in fully ON state. In this region the transistor acts as a closed circuit.

The gate voltage at which the transistor ON and starts the current flow through the channel is called threshold voltage. This threshold voltage value range for N-channel devices is in between 0.5V to 0.7V and for P-channel devices is in between -0.5V to -0.8V.

The behavior of a MOSFET transistor in depletion and enhancement modes depending on the gate voltage is summarized as follows.

Applications

• MOSFETs are used in digital integrated circuits, such as microprocessors.
• Used in calculators.
• Used in memories and in logic CMOS gates.
• Used as analog switches.
• Used as amplifiers.
• Used in the applications of power electronics and switch mode power supplies.
• MOSFETs are used as oscillators in radio systems.
• Used in automobile sound systems and in sound reinforcement systems.

Conclusion

A complete beginner’s guide to introduction of MOSFET. You learned the structure of a MOSFET, different types of MOSFET, their circuit symbols, an example circuit using a MOSFET to control an LED and also few areas of applications.