For the Smart Home system, the main task is to control household appliances from a control device, be it an Arduino-type microcontroller, or a Raspberry PI-type microcomputer, or any other. But it won’t be possible to do this directly, let’s figure out how to control a 220 V load with Arduino.

A microcontroller is not enough to control AC circuits for two reasons:

1. At the exit microcontroller a constant voltage signal is generated.

2. The current through the microcontroller pin is usually limited to 20-40 mA.

We have two options for switching using a relay or using a triac. The triac can be replaced by two thyristors connected back-to-back (this is the internal structure of the triac). Let's take a closer look at this.

Controlling a 220 V load using a triac and microcontroller

The internal structure of the triac is shown in the picture below.

The thyristor works as follows: when a forward bias voltage is applied to the thyristor (plus to the anode and minus to the cathode), no current will pass through it until you apply a control pulse to the control electrode.

I wrote impulse for a reason. Unlike a transistor, a thyristor is a SEMI-CONTROLLED semiconductor switch. This means that when the control signal is removed, the current through the thyristor will continue to flow, i.e. it will remain open. In order for it to close, you need to interrupt the current in the circuit or change the polarity of the applied voltage.

This means that while maintaining a positive pulse on the control electrode, the thyristor in the alternating current circuit will transmit only the positive half-wave. A triac can pass current in both directions, but since it consists of two thyristors connected towards each other.

The polarity of control pulses for each of the internal thyristors must correspond to the polarity of the corresponding half-wave; only if this condition is met, alternating current will flow through the triac. In practice, such a scheme is implemented in the common .

As I already said, the microcontroller produces a signal of only one polarity; in order to match the signal, you need to use a driver built on an optosimistor.

Thus, the signal turns on the internal LED of the optocoupler, it opens the triac, which supplies the control signal to the power triac T1. MOC3063 and similar ones can be used as an optodriver, for example, the photo below shows MOC3041.

Zero crossing circuit - phase transition detector circuit through zero. Needed to implement various types of triac regulators on a microcontroller.

If the circuit does not have an optodriver, where the matching is organized through a diode bridge, but, unlike the previous version, there is no galvanic isolation. This means that at the first voltage surge, the bridge may break through and high voltage will appear at the microcontroller pin, which is bad.

When turning on/off a powerful load, especially an inductive one, such as motors and electromagnets, voltage surges occur, so a snubber RC circuit must be installed in parallel with all semiconductor devices.

Relay and Arduino

To control a relay with an Arduino, you need to use an additional transistor to amplify the current.

Please note that a reverse conduction bipolar transistor (NPN structure) is used; it can be the domestic KT315 (beloved and known to everyone). A diode is needed to dampen bursts of self-induction EMF in the inductance; this is necessary so that the transistor does not fail from the high applied voltage. Why this occurs will be explained by the commutation law: “The current in an inductance cannot change instantly.”

And when the transistor is closed (the control pulse is removed), the energy of the magnetic field accumulated in the relay coil needs to go somewhere, which is why a reverse diode is installed. Once again, I note that the diode is connected in the REVERSE direction, i.e. cathode to positive, anode to negative.

You can assemble such a circuit with your own hands, which is much cheaper, plus you can use one designed for any DC voltage.

Or buy a ready-made module or a whole shield with a relay for Arduino:

The photo shows a homemade shield, by the way, it uses KT315G to amplify the current, and below you see the same factory-made shield:

Conclusion

Safe control of an AC load implies, first of all, all the information described above is valid for any microcontroller, not just the Arduino board.

The main task is to provide the necessary voltage and current to control the triac or relay and galvanic isolation of the control circuits and the AC power circuit.

In addition to safety for the microcontroller, in this way you protect yourself so that you do not receive electrical injury during servicing. When working with high voltage, you must follow all safety rules, comply with the PUE and PTEEP.

These schemes can also be used. Triacs and relays in this case act as an intermediate amplifier and signal matcher. On powerful switching devices, the coil control currents are large and depend directly on the power of the contactor or starter.

Alexey Bartosh

Transistor

A transistor is a semiconductor device that allows you to control a stronger signal using a weak signal. Because of this property, they often talk about the ability of a transistor to amplify a signal. Although in fact, it does not enhance anything, but simply allows you to turn on and off a large current with much weaker currents. Transistors are very common in electronics, because the output of any controller can rarely produce a current of more than 40 mA, therefore, even 2-3 low-power LEDs cannot be powered directly from the microcontroller. This is where transistors come to the rescue. The article discusses the main types of transistors, the differences between P-N-P and N-P-N bipolar transistors, P-channel and N-channel field-effect transistors, discusses the main subtleties of connecting transistors and reveals their scope of application.

Do not confuse a transistor with a relay. A relay is a simple switch. The essence of its work is to close and open metal contacts. The transistor is more complex and its operation is based on an electron-hole transition. If you are interested in learning more about this, you can watch an excellent video that describes the operation of a transistor from simple to complex. Don’t be confused by the year the video was produced - the laws of physics have not changed since then, and a newer video that presents the material so well could not be found:

Types of transistors

Bipolar transistor

The bipolar transistor is designed to control weak loads (for example, low-power motors and servos). It always has three outputs:

Collector - a high voltage is supplied, which the transistor controls

• Base - current is supplied or turned off to open or close the transistor

Emitter (English: emitter) - “output” output of a transistor. Current flows through it from the collector and base.

The bipolar transistor is controlled by current. The more current supplied to the base, the more current will flow from the collector to the emitter. The ratio of the current passing from the emitter to the collector to the current at the base of the transistor is called the gain. Denoted as hfe (in English literature it is called gain).

For example, if hfe= 150, and 0.2 mA passes through the base, then the transistor will pass a maximum of 30 mA through itself. If a component that draws 25 mA (such as an LED) is connected, 25 mA will be provided to it. If a component that draws 150 mA is connected, it will only be provided with the maximum 30 mA. The documentation for the contact indicates the maximum permissible values ​​of currents and voltages base-> emitter And collector -> emitter . Exceeding these values ​​leads to overheating and failure of the transistor.

Funny pictures:

NPN and PNP bipolar transistors

There are 2 types of polar transistors: NPN And PNP. They differ in the alternation of layers. N (from negative) is a layer with an excess of negative charge carriers (electrons), P (from positive) is a layer with an excess of positive charge carriers (holes). More information about electrons and holes is described in the video above.

The behavior of transistors depends on the alternation of layers. The animation above shows NPN transistor. IN PNP transistor control is the other way around - current flows through the transistor when the base is grounded and is blocked when current is passed through the base. As shown in the diagram PNP And NPN differ in the direction of the arrow. The arrow always points to the transition from N To P:

Designation of NPN (left) and PNP (right) transistors in the diagram

NPN transistors are more common in electronics because they are more efficient.

Field effect transistor

Field-effect transistors differ from bipolar transistors in their internal structure. MOS transistors are the most common in amateur electronics. MOS is an acronym for metal-oxide-conductor. The same in English: Metal-Oxide-Semiconductor Field Effect Transistor, abbreviated as MOSFET. MOS transistors allow you to control high powers with relatively small sizes of the transistor itself. The transistor is controlled by voltage, not current. Since the transistor is controlled by electrical field, the transistor got its name - field howl.

Field effect transistors have at least 3 terminals:

Drain - high voltage is applied to it, which you want to control

Gate - voltage is applied to it to control the transistor

Source - current flows through it from the drain when the transistor is “open”

There should be an animation with a field-effect transistor, but it will not differ in any way from a bipolar transistor except for the schematic display of the transistors themselves, so there will be no animation.

N channel and P channel field effect transistors

Field-effect transistors are also divided into 2 types depending on the device and behavior. N channel(N channel) opens when voltage is applied to the gate and closes. when there is no voltage. P channel(P channel) works the other way around: while there is no voltage at the gate, current flows through the transistor. When voltage is applied to the gate, the current stops. In the diagram, field-effect transistors are depicted slightly differently:

By analogy with bipolar transistors, field transistors differ in polarity. The N-Channel transistor was described above. They are the most common.

P-Channel when designated differs in the direction of the arrow and, again, has an “inverted” behavior.

There is a misconception that a field effect transistor can control alternating current. This is wrong. To control alternating current, use a relay.

Darlington transistor

It is not entirely correct to classify the Darlington transistor as a separate type of transistor. However, it is impossible not to mention them in this article. The Darlington transistor is most often found in the form of a microcircuit that includes several transistors. For example, ULN2003. The Darlington transistor is characterized by the ability to quickly open and close (and therefore allows you to work with) and at the same time withstand high currents. It is a type of compound transistor and is a cascade connection of two or, rarely, more transistors connected in such a way that the load in the emitter of the previous stage is the base-emitter junction of the transistor of the next stage, that is, the transistors are connected by collectors, and the emitter of the input transistor is connected to the base day off. In addition, the resistive load of the emitter of the previous transistor can be used as part of the circuit to speed up the closing. Such a connection as a whole is considered as one transistor, the current gain of which, when the transistors are operating in the active mode, is approximately equal to the product of the gains of all transistors.

Transistor connection

It is no secret that the Arduino board is capable of supplying a voltage of 5 V to the output with a maximum current of up to 40 mA. This current is not enough to connect a powerful load. For example, if you try to connect an LED strip or motor directly to the output, you are guaranteed to damage the Arduino output. It is possible that the entire board will fail. Additionally, some connected components may require more than 5V to operate. The transistor solves both of these problems. It will help, using a small current from the Arduino pin, to control a powerful current from a separate power supply, or using a voltage of 5 V to control a higher voltage (even the weakest transistors rarely have a maximum voltage below 50 V). As an example, consider connecting a motor:

In the diagram above, the motor is connected to a separate power source. Between the motor contact and the power supply for the motor, we placed a transistor, which will be controlled using any Arduino digital pin. When we apply a HIGH signal to the controller output from the controller output, we will take a very small current to open the transistor, and a large current will flow through the transistor and will not damage the controller. Pay attention to the resistor installed between the Arduino pin and the base of the transistor. It is needed to limit the current flowing along the microcontroller - transistor - ground route and prevent short circuits. As mentioned earlier, the maximum current that can be drawn from the Arduino pin is 40 mA. Therefore, we will need a resistor of at least 125 Ohm (5V/0.04A=125 Ohm). You can safely use a 220 Ohm resistor. In fact, the resistor should be selected taking into account the current that must be supplied to the base to obtain the required current through the transistor. To select the correct resistor, you need to take into account the gain factor ( hfe).

IMPORTANT!! If you connect a powerful load from a separate power supply, then you need to physically connect the ground (“minus”) of the load power supply and the ground (“GND” pin) of the Arduino. Otherwise, you won’t be able to control the transistor.

When using a field effect transistor, a current limiting resistor on the gate is not needed. The transistor is controlled solely by voltage and no current flows through the gate.

Over time, each user Arduino thinks about controlling not only LEDs and devices with voltages up to 5 volts, but also about controlling solenoids, motors, LED strips, etc., which use 12 volts or more. This article will look at how you can work with high voltage using MOSFET And arduino.

This article will discuss MOSFET transistor - metal-oxide-semiconductor field-effect transistor, in particular** RFP30N06LE**, but you can also work with others.

Let's begin with MOSFET It's a transistor, but of a special type.
Transistors have 3 outputs, which have 2 simple functions, the first is switching, the second is amplification (in this example, the first function is considered - a switch). The outputs are named as follows: Input (Source), aka Source, Output (Drain) - Drain, and Control (Gate, Shutter) - Gate. When sending a high level signal to Gate (control pin), transistor turns on and allows current to flow from Source to Drain.

So we will connect our motor, solenoid or lamp to V+, but not to ground (V-). We connect the ground to the drain (Drain) of the transistor. When our Arduino sends a high level signal to the Gate transistor, it switches the transistor (connects Source and Drain) and completes the circuit for the motor, solenoid, or lamp.

We connect the motor to Arduino (diagram 1)

Connect the solenoid to the Arduino (diagram 2)

Connect the llama to the Arduino (diagram 3)

Connection / Why is the diode used?

This scheme is quite simple. The only part that raises questions is the use Pull down resistor. Resistor holds Gate low when Arduino does not send a high level signal. The point is that if the wires are bad, for example, the signal may float, and when Arduino does not send a signal, residual voltage may remain and transistor may turn on spontaneously. Resistor It also pulls the residual stress towards the ground.

You can also notice a diode in diagrams 1 and 2. When connecting a device with a coil (Coil), be it a relay, solenoid or motor, always use a diode. What happens if we don't use it? When you stop feeding the coil, the reverse voltage, sometimes up to several hundred volts, is sent back. It only lasts a few microseconds, but it's enough to kill our MOSFET. So this diode allows current to flow one way, usually in the wrong orientation, and does nothing. But when a voltage surge occurs and current flows in the opposite direction, the diode allows it to flow back to the coil rather than to the transistor.

We will need a diode that is fast enough to respond to recoil, and strong enough to carry the load. Diodes are suitable for us 1N4001 or SB560. If you need additional protection, you can use an opto-isolator between Arduino and a transistor. The opto-isolator isolates both sides of the circuit, and high voltage will not be able to return to the microcontroller, and will not kill it.

Also be sure to connect the diode correctly! A stripe (usually silver) to the plus (V+), otherwise it will be of no use, and can make it even worse.

Disadvantages/Limitations

Transistors such as RFP30N06LE suitable for controlling powerful devices from your Arduino, but they have some limitations. This current configuration only makes sense for switching DC current, so don't try this with an AC source as well MOSFET-transistors have limitations such as voltage and current. RFP30N06LE can handle switching up to 60V, and the current is limited to 30A (with a heatsink and proper connection), it is also extremely important to use a heat sink when the current is more than a few amperes, since in this case a fairly large amount of heat is generated when the transistor operates.

You can usually just solder a curved piece of metal to the back, just to dissipate the heat. Please note that when using several transistors, do not solder to a common heatsink, use a separate heatsink for each transistor, since these transistors have the back connected to the Output (Drain)! It is important. I also want to note that for AC current it is better to use a relay.

Fade it / Use PWM

You know on Arduino There is PWM(PWM) outputs, why don't we use them? Yes, PWM- this is what allows you to use analogWrite(PIN, value). PWM not really an analog output. Arduino really pulsates (very quickly) from 0 to 5V so the average voltage is somewhere between 0 and 5V. We can connect to PWM output our transistor and control the brightness of the light, motor speed, etc. as if we had connected them directly to Arduino. To do this, you just need to make sure that the transistor is connected to PWM exit Arduino.

Code/Sketch for Arduino

You probably won't need this code, you just send a high level signal to Gate and BAM... It works. But I've sketched out the code for you so you can test it using PWM. (Only makes sense for a motor or light bulb, not a solenoid).

//////////////////////////////////////////////// //////////////// //Released under the MIT License - Please reuse change and share //Simple code to output a PWM sine wave signal on pin 9 /////// //////////////////////////////////////////////// ///////// #define fadePin 3 void setup())( pinMode(fadePin, OUTPUT); ) void loop())( for(int i = 0; i<360; i++){ //convert 0-360 angle to radian (needed for sin function) float rad = DEG_TO_RAD * i; //calculate sin of angle as number between 0 and 255 int sinOut = constrain((sin(rad) * 128) + 128, 0, 255); analogWrite(fadePin, sinOut); delay(15); } }

MOP (in bourgeois MOSFET) stands for Metal-Oxide-Semiconductor, from this abbreviation the structure of this transistor becomes clear.

If on the fingers, then it has a semiconductor channel that serves as one plate of the capacitor and the second plate is a metal electrode located through a thin layer of silicon oxide, which is a dielectric. When voltage is applied to the gate, this capacitor is charged, and the electric field of the gate pulls charges to the channel, as a result of which mobile charges appear in the channel that can form an electric current and the drain-source resistance drops sharply. The higher the voltage, the more charges and lower the resistance, as a result, the resistance can drop to tiny values ​​- hundredths of an ohm, and if you raise the voltage further, a breakdown of the oxide layer and the Khan transistor will occur.

The advantage of such a transistor, compared to a bipolar one, is obvious - voltage must be applied to the gate, but since it is a dielectric, the current will be zero, which means the required the power to control this transistor will be scanty, in fact, it only consumes at the moment of switching, when the capacitor is charging and discharging.

The disadvantage arises from its capacitive property - the presence of capacitance on the gate requires a large charging current when opening. In theory, equal to infinity on infinitely small periods of time. And if the current is limited by a resistor, then the capacitor will charge slowly - there is no escape from the time constant of the RC circuit.

MOS transistors are P and N duct. They have the same principle, the only difference is the polarity of the current carriers in the channel. Accordingly, in different directions of the control voltage and inclusion in the circuit. Very often transistors are made in the form of complementary pairs. That is, there are two models with exactly the same characteristics, but one of them is N channel, and the other is P channel. Their markings, as a rule, differ by one digit.

My most popular MOP transistors are IRF630(n channel) and IRF9630(p channel) at one time I made about a dozen of them of each type. Possessing a not very large body TO-92 this transistor can famously pull through itself up to 9A. Its open resistance is only 0.35 Ohm.
However, this is a fairly old transistor; now there are cooler things, for example IRF7314, capable of carrying the same 9A, but at the same time it fits into an SO8 case - the size of a notebook square.

One of the docking problems MOSFET transistor and microcontroller (or digital circuit) is that in order to fully open until completely saturated, this transistor needs to drive quite a bit more voltage onto the gate. Usually this is about 10 volts, and the MK can output a maximum of 5.
There are three options:

But in general, it is more correct to install a driver, because in addition to the main functions of generating control signals, it also provides current protection, protection against breakdown, overvoltage, as an additional bauble, optimizes the opening speed to the maximum, in general, it does not consume its current in vain.

Choosing a transistor is also not very difficult, especially if you don’t bother with limiting modes. First of all, you should be concerned about the value of the drain current - I Drain or I D you choose a transistor based on the maximum current for your load, preferably with a margin of 10 percent. The next important parameter for you is VGS- Source-Gate saturation voltage or, more simply, control voltage. Sometimes it is written, but more often you have to look at the charts. Looking for a graph of the output characteristic Dependency I D from VDS at different values VGS. And you figure out what kind of regime you will have.

For example, you need to power the engine at 12 volts, with a current of 8A. You screwed up the driver and only have a 5 volt control signal. The first thing that came to mind after this article was IRF630. The current is suitable with a margin of 9A versus the required 8. But let’s look at the output characteristic:

If you are going to use PWM on this switch, then you need to inquire about the opening and closing times of the transistor, choose the largest one and, relative to the time, calculate the maximum frequency of which it is capable. This quantity is called Switch Delay or t on,t off, in general, something like this. Well, the frequency is 1/t. It’s also a good idea to look at the gate capacity C iss Based on it, as well as the limiting resistor in the gate circuit, you can calculate the charging time constant of the RC gate circuit and estimate the performance. If the time constant is greater than the PWM period, then the transistor will not open/close, but will hang in some intermediate state, since the voltage at its gate will be integrated by this RC circuit into a constant voltage.

When handling these transistors, keep in mind the fact that They are not just afraid of static electricity, but VERY STRONG. It is more than possible to penetrate the shutter with a static charge. So how did I buy it? immediately into foil and don’t take it out until you seal it. First ground yourself to the battery and put on a foil hat :).

Using optothyristors

Optosimistors MOS301x, MOS302x, MOS303x, MOS304x, MOS306x, MOS308x
Optosimistors belong to the class of optocouplers and provide very good galvanic isolation (about 7500 V) between the control circuit and the load. These radioelements consist of an infrared LED connected via an optical channel to a bidirectional silicon triac. The latter can be supplemented with an unlocking circuit that is triggered when the supply voltage passes through zero.
These radioelements are especially indispensable when controlling more powerful triacs, for example, when implementing high voltage or high power relays. Such optocouplers were conceived to communicate between logic circuits with low voltage levels and a load powered by a mains voltage of 220 V. The optosimistor can be placed in a small-sized DIP package with six pins; its pinout and internal structure are shown in Fig. 1.

The table shows the classification of optosimistors according to the magnitude of the forward current through the IFT LED, which opens the device, and the maximum forward repeating voltage that the triac can withstand at the output (VDRM). The table also notes the property of the triac to open when the supply voltage passes through zero. To reduce interference, it is preferable to use triacs that open when the supply voltage passes through zero.

As for elements with zero supply voltage detection, their output stage is triggered when the supply voltage exceeds a certain threshold, usually 5 V (maximum 20 V). The MOS301x and MOS302x series are more often used with resistive loads or in cases where the load supply voltage must be turned off. When a triac is in a conducting state, the maximum voltage drop across its terminals is usually 1.8V (maximum 3V) at a current of up to 100mA. The holding current (IH), which maintains the conductivity of the output stage of the optosimistor, is equal to 100 μA, whatever it is (negative or positive) during the half-cycle of the supply voltage.
The off-state leakage current of the output stage (ID) varies depending on the optosimistor model. For optosimistors with zero detection, the leakage current can reach 0.5mA if the LED is energized (current flowing IF).
The infrared LED has a reverse leakage current of 0.05 µA (maximum 100 µA), and a maximum forward voltage drop of 1.5 V for all optosimistor models. The maximum permissible LED reverse voltage is 3 volts for models MOS301x, MOS302x and MOS303x and 6 volts for models MOS304x. MOSZO6x and MOSZO8x.
Maximum permissible characteristics
The maximum permissible current through the LED in continuous mode is no more than 60mA.
The maximum pulse current in the conducting state of the output stage switch is no more than 1 A.
The total power dissipation of the optosimistor should not exceed 250 mW (maximum 120 mW for the LED and 150 mW for the output stage at T - 25˚C).

Application of optosimistors

Figure 2 a-e shows various diagrams of typical applications of optosimistors, differing from each other in the nature of the load and the methods of connecting the load and power.
Resistance Rd
The calculation of the resistance of this resistor depends on the minimum forward current of the infrared LED, which guarantees the triggering of the triac. Therefore, Rd = (+V - 1.5) / IF.
For example, for a transistor control circuit for an optosimistor with a supply voltage of +5 V (Fig. 3) and an open transistor voltage (Uke us) equal to 0.3 V, +V will be 4.7 V, and IF should be in the range between 15 and 50 ma for MOS3041. IF - 20 mA should be taken taking into account the decrease in LED efficiency over the service life (5 mA reserve), fully ensuring the operation of the optocoupler with a gradual weakening of the current. Thus we have:
Rв = (4.7 - 1.5) / 0.02 = 160 Ohm.
You should select a standard resistance value, that is, 150 Ohms for MOS3041 and a resistance of 100 Ohms for MOS3020.
Resistance R
Resistor R does not need to be included when the load is purely resistive. However, if the triac is protected by an RP - CP circuit, most often called a spark-extinguishing circuit, resistor R makes it possible to limit the current through the control electrode of the optosimistor. Indeed, in the case of an inductive load, the current passing through the triac and the voltage applied to the circuit are in antiphase. Since the triac ceases to be a conductor when the current passes through zero, the CP protection circuit capacitor can discharge through the optosimistor. Then resistor R limits this discharge current. The minimum value of its resistance depends on the maximum voltage of the capacitor and the maximum permissible current for the optosimistor, therefore for a supply voltage of 220 V:
Rmin = 220 V x 1.41 / 1A - 311 Ohm.
On the other hand, too large an R value can lead to malfunction. Therefore, they accept R - 330 or 390 Ohms.
RG resistance
The RG resistor is needed only when the input resistance of the control electrode is very high, that is, in the case of a sensitive triac. The value of resistor RG can be in the range from 100 to 500 ohms.
Resistors RG and R introduce a delay in unlocking the triac, which will be more significant the higher the resistance of these resistors. Chain Ra - Ca
To limit the rate of change in voltage dV/dt at the output of the optosimistor, a snubber circuit is needed (Fig. 2d).
The choice of the value of the resistor Ra depends on the sensitivity of the triac and the voltage Va, starting from which the triac should operate. Thus we have:
R + Ra = Va / IG.
For a triac with control current IG = 25mA and trigger voltage Va = 20V we get: R + Ra = 20 / 0.025 - 800 Ohm
or: Ra = 800 - 330 = 470 Ohm.
In order for the triac to switch quickly, the following condition must be met: dV / dt = 311 / Ra x Ca.
For MOS3020, the maximum dV / dt value is 10 V/µs.
Thus: Ca = 311 / (470 x 107) = 66 nF.
We choose: Ca = 68 nF.
Comment.
As for the snubber chain, experimental values ​​are generally preferable to theoretical calculations.
Protection
It is strongly recommended to protect the triac and optosimistor when operating on an inductive load or when interference frequently affects the network.
For a triac, a spark-extinguishing RC circuit is simply necessary. For an optosimistor with zero detection, such as the MOS3041, this is desirable. The resistance of resistor R should be increased from 27 Ohms to 330 Ohms (except for the case when the controlled triac is insensitive).
If a model without zero detection is used, then the snubber chain Ra - Ca is required.