The 555 timer is widely used in control devices, for example, in PWM - speed controllers for DC motors.
Anyone who has ever used a cordless screwdriver has probably heard a squeaking sound coming from inside. This is the whistling of the motor windings under the influence of the pulse voltage generated by the PWM system.
It is simply indecent to regulate the speed of an engine connected to a battery in another way, although it is quite possible. For example, simply connect a powerful rheostat in series with the motor, or use an adjustable linear voltage regulator with a large radiator.
A variant of a PWM regulator based on a 555 timer is shown in Figure 1.
The circuit is quite simple and is based on a multivibrator, albeit converted into a pulse generator with an adjustable duty cycle, which depends on the ratio of the charge and discharge rates of capacitor C1.
The capacitor is charged through the circuit: +12V, R1, D1, the left side of the resistor P1, C1, GND. And the capacitor is discharged along the circuit: upper plate C1, right side of resistor P1, diode D2, pin 7 of the timer, bottom plate C1. By rotating the slider of resistor P1, you can change the ratio of the resistances of its left and right parts, and therefore the charging and discharging time of capacitor C1, and, as a consequence, the duty cycle of the pulses.
Figure 1. PWM regulator circuit on a 555 timer
This scheme is so popular that it is already available in the form of a set, as shown in the following figures.
Figure 2. Schematic diagram of a set of PWM regulators.
Timing diagrams are also shown here, but, unfortunately, the part values are not shown. They can be seen in Figure 1, which is why it is shown here. Instead of bipolar transistor TR1, without altering the circuit, you can use a powerful field effect one, which will increase the load power.
By the way, another element has appeared in this diagram - diode D4. Its purpose is to prevent the timing capacitor C1 from discharging through the power source and the load - the motor. This ensures stabilization of the PWM frequency.
By the way, with the help of such circuits you can control not only the speed of a DC motor, but also simply an active load - an incandescent lamp or some kind of heating element.
Figure 3. Printed circuit board of a PWM regulator kit.
If you put in a little work, it is quite possible to recreate this using one of the programs for drawing printed circuit boards. Although, given the small number of parts, it will be easier to assemble one copy using a hinged installation.
Figure 4. Appearance of a set of PWM regulators.
True, the already assembled branded set looks quite nice.
Here, perhaps, someone will ask a question: “The load in these regulators is connected between +12V and the collector of the output transistor. But what about, for example, in a car, because everything there is already connected to the ground, the body, of the car?”
Yes, you can’t argue against the mass; here we can only recommend moving the transistor switch to the gap in the “positive” wire. A possible version of such a scheme is shown in Figure 5.
Figure 5.
Figure 6 shows the MOSFET output stage separately. The drain of the transistor is connected to +12V of the battery, the gate simply “hangs” in the air (which is not recommended), a load is connected to the source circuit, in our case a light bulb. This figure is shown simply to explain how a MOSFET transistor works.
Figure 6.
In order to open a MOSFET transistor, it is enough to apply a positive voltage to the gate relative to the source. In this case, the light bulb will light up at full intensity and will shine until the transistor is closed.
In this figure, the easiest way to turn off the transistor is to short-circuit the gate to the source. And such a manual closure is quite suitable for checking the transistor, but in a real circuit, especially a pulse circuit, you will have to add a few more details, as shown in Figure 5.
As mentioned above, an additional voltage source is required to turn on the MOSFET transistor. In our circuit, its role is played by capacitor C1, which is charged via the +12V circuit, R2, VD1, C1, LA1, GND.
To open transistor VT1, a positive voltage from a charged capacitor C2 must be applied to its gate. It is quite obvious that this will only happen when transistor VT2 is open. And this is only possible if the optocoupler transistor OP1 is closed. Then the positive voltage from the positive plate of capacitor C2 through resistors R4 and R1 will open transistor VT2.
At this moment, the input PWM signal must be at a low level and bypass the optocoupler LED (this LED switching is often called inverse), therefore, the optocoupler LED is off and the transistor is closed.
To turn off the output transistor, you need to connect its gate to the source. In our circuit, this will happen when transistor VT3 opens, and this requires that the output transistor of the optocoupler OP1 be open.
The PWM signal at this time is at a high level, so the LED is not shunted and emits the infrared rays assigned to it, the optocoupler transistor OP1 is open, which as a result turns off the load - the light bulb.
One of the options for using such a scheme in a car is daytime running lights. In this case, motorists claim to use high beam lamps turned on at full intensity. Most often, these designs are on a microcontroller; there are plenty of them on the Internet, but it’s easier to do it on a 555 timer.
Drivers for MOSFET transistors on 555 timer
The 555 integrated timer found another application in three-phase inverters, or as they are more often called variable frequency drives. The main purpose of “frequency drivers” is to regulate the rotation speed of three-phase asynchronous motors. In the literature and on the Internet you can find many schemes of homemade frequency drives, interest in which has not disappeared to this day.
In general the idea is this. The rectified mains voltage is converted into three-phase using the controller, as in an industrial network. But the frequency of this voltage can change under the influence of the controller. The methods of change are different, from simply manual control to regulation by an automatic system.
The block diagram of a three-phase inverter is shown in Figure 1. Points A, B, C show the three phases to which the asynchronous motor is connected. These phases are obtained by switching transistor switches, which are shown in this figure as special IGBT transistors.
Figure 1. Block diagram of a three-phase inverter
The inverter power switch drivers are installed between the control device (controller) and the power switches. Specialized microcircuits such as IR2130 are used as drivers, allowing you to connect all six keys to the controller at once - three upper and three lower, and in addition, it also provides a whole range of protections. All details about this chip can be found in the Data Sheet.
And everything would be fine, but such a microcircuit is too expensive for home experiments. And here our old friend integrated timer 555, also known as KR1006VI1, comes to the rescue again. The diagram of one arm of a three-phase bridge is shown in Figure 2.
Figure 2. Drivers for MOSFET transistors on a 555 timer
KR1006VI1 operating in Schmitt trigger mode are used as drivers for the upper and lower switches of power transistors. When using a timer in this mode, it is enough to simply obtain a gate opening pulse current of at least 200 mA, which ensures fast switching of the output transistors.
The transistors of the lower keys are connected directly to the common wire of the controller, so there are no difficulties in controlling the drivers - the lower drivers are controlled directly from the controller by logical signals.
The situation with the upper keys is somewhat more complicated. First of all, you should pay attention to how the upper key drivers are powered. This method of nutrition is called “booster”. Its meaning is as follows. The DA1 microcircuit is powered by capacitor C1. But how can it be charged?
When transistor VT2 opens, the negative plate of capacitor C1 is practically connected to the common wire. At this time, capacitor C1 is charged from the power source through diode VD1 to a voltage of +12V. When the transistor VT2 closes, the diode VD1 will also close, but the energy reserve in the capacitor C1 is enough to trigger the DA1 chip in the next cycle. To achieve galvanic isolation from the controller and among themselves, the upper keys must be controlled through optocoupler U1.
This power supply method allows you to get rid of the complexity of the power supply and get by with just one voltage. Otherwise, three isolated windings on the transformer, three rectifiers and three stabilizers would be required. More details about this method of power supply can be found in the descriptions of specialized microcircuits.
Boris Aladyshkin, http://electrik.info
Good evening friends! This is my first review of anything in my life, so I’m happy to listen to criticism and advice.
The goods were bought with their own money. Details below.
I was prompted to order this regulator by my respected kirich. Therefore, I first ordered exactly the same PWM regulator, but then, for a change, I ordered the hero of today’s review.
The order was placed on October 29, but it only reached me in Lobnya near Moscow on December 3. The product was packed in a standard bag with bubble wrap and generously wrapped in foam:
Package
The kit includes only the control board itself and a 100 kOhm variable resistor, which is connected directly to the board using a HU-3 connector with a wire length of 19 cm, which is quite convenient for installation.
The soldering of power traces seemed simply terrible to me. I didn’t think that our Asian friends would skimp on solder. There are also many traces of unwashed flux visible. Maybe I'm just that lucky:
I don’t pretend to be a soldering guru, so I decided to correct the situation a little. I think if someone received payment after my hands, they wouldn’t be much different from the Chinese:
The regulator is built on the NE555P timer, so I think it makes no sense to talk about the entire circuit, and I’m afraid I don’t have enough knowledge for this yet =).
The operating voltage range is 12-60 Volts and the maximum current is 20 Amps. By the way, in one of the photos you can see a 20 Ampere fuse, which in theory should save you from exceeding the rated current.
Now let's check it in action. For power I will use an old power supply from a laptop with 19 Volts and 4.74 Amps, and a motor from some kind of screwdriver with 18 Volts:
Video of the work itself. I apologize for the slight shaking, because... I filmed it on my phone, but I don’t have a tripod for this:
To buy or not is everyone's business. I bought this for a mini drill press that I hope to start building in the coming year. Of course, the network is full of schemes on this topic, but for now, as a beginner, I wanted a ready-made solution.
Thank you all for your attention, I look forward to your comments!
Instead of kote
Any modern power tool or household appliance uses a commutator motor. This is due to their versatility, i.e. the ability to operate on both alternating and direct voltage. Another advantage is the efficient starting torque.
However, the high speed of the commutator motor does not suit all users. For a smooth start and the ability to change the speed of rotation, a regulator was invented, which is quite possible to make with your own hands.
Operating principle and types of commutator motors
Each electric motor consists of a commutator, stator, rotor and brushes. The principle of its operation is quite simple:
In addition to the standard device, there are also:
Regulator device
There are many schemes of such devices in the world. Nevertheless, they can all be divided into 2 groups: standard and modified products.
Standard device
Typical products are distinguished by ease of manufacture of the idynistor and good reliability when changing engine speed. As a rule, such models are based on thyristor regulators. The operating principle of such schemes is quite simple:
Thus, the speed of the commutator motor is adjusted. In most cases, a similar scheme is used in foreign household vacuum cleaners. However, you should know that such a speed controller does not have feedback. Therefore, when the load changes, you will have to adjust the speed of the electric motor.
Changed schemes
Of course, the standard device suits many fans of speed controllers to “dig” into the electronics. However, without progress and improvement of products, we would still be living in the Stone Age. Therefore, more interesting schemes are constantly being invented, which many manufacturers are happy to use.
The most commonly used are rheostat and integral regulators. As the name implies, the first option is based on a rheostat circuit. In the second case, an integral timer is used.
Rheostatic ones are effective in changing the number of revolutions of the commutator motor. High efficiency is due to power transistors, which take part of the voltage. Thus, the current flow is reduced and the motor works with less effort.
Video: speed control device with power maintenance
The main disadvantage of this scheme is the large amount of heat generated. Therefore, for smooth operation, the regulator must be constantly cooled. Moreover, the cooling of the device must be intensive.
A different approach is implemented in an integral regulator, where an integral timer is responsible for the load. As a rule, transistors of almost any type are used in such circuits. This is due to the fact that it contains a microcircuit with large output current values.
If the load is less than 0.1 ampere, then all the voltage goes directly to the microcircuit, bypassing the transistors. However, for the regulator to operate effectively, it is necessary that there be a voltage of 12V at the gate. Therefore, the electrical circuit and the supply voltage itself must correspond to this range.
Overview of typical circuits
You can regulate the rotation of the shaft of a low-power electric motor by connecting a power resistor in series with no. However, this option has very low efficiency and the inability to smoothly change speed. To avoid such a nuisance, you should consider several regulator circuits that are used most often.
As you know, PWM has a constant pulse amplitude. In addition, the amplitude is identical to the supply voltage. Consequently, the electric motor will not stop even when running at low speeds.
The second option is similar to the first. The only difference is that an operational amplifier is used as the master oscillator. This component has a frequency of 500 Hz and produces triangular-shaped pulses. Adjustment is also carried out using a variable resistor.
How to make it yourself
If you don’t want to spend money on purchasing a ready-made device, you can make it yourself. This way, you can not only save money, but also gain useful experience. So, to make a thyristor regulator you will need:
- soldering iron (to check functionality);
- wires;
- thyristor, capacitors and resistors;
- scheme.
As can be seen from the diagram, the regulator controls only 1 half-cycle. However, for testing performance on a regular soldering iron, this will be quite enough.
If you don’t have enough knowledge to decipher the diagram, you can familiarize yourself with the text version:
The use of regulators allows for more economical use of electric motors. In certain situations, such a device can be made independently. However, for more serious purposes (for example, monitoring heating equipment), it is better to purchase a ready-made model. Fortunately, there is a wide selection of such products on the market, and the price is quite affordable.
You can adjust the rotation speed of the shaft of a low-power commutator motor by connecting it in series to its power supply circuit. But this option creates a very low efficiency, and in addition there is no possibility of smoothly changing the rotation speed.
The main thing is that this method sometimes leads to a complete stop of the electric motor at low supply voltage. Electric motor speed controller The DC circuits described in this article do not have these disadvantages. These circuits can also be successfully used to change the brightness of 12-volt incandescent lamps.
Description of 4 electric motor speed controller circuits
First scheme
The rotation speed is changed by variable resistor R5, which changes the duration of the pulses. Since the amplitude of the PWM pulses is constant and equal to the supply voltage of the electric motor, it never stops even at a very low rotation speed.
Second scheme
It is similar to the previous one, but the operational amplifier DA1 (K140UD7) is used as the master oscillator.
This op-amp functions as a voltage generator producing triangular-shaped pulses and having a frequency of 500 Hz. Variable resistor R7 sets the rotation speed of the electric motor.
Third scheme
It is unique, built on it. The master oscillator operates with a frequency of 500 Hz. The pulse width, and therefore the engine speed, can be changed from 2% to 98%.
The weak point in all the above schemes is that they do not have an element for stabilizing the rotation speed when the load on the DC motor shaft increases or decreases. You can resolve this problem using the following diagram:
Like most similar regulators, the circuit of this regulator has a master voltage generator that produces triangular pulses with a frequency of 2 kHz. The entire specificity of the circuit is the presence of positive feedback (POS) through elements R12, R11, VD1, C2, DA1.4, which stabilizes the rotation speed of the electric motor shaft when the load increases or decreases.
When setting up a circuit with a specific motor, resistance R12, choose a PIC depth at which self-oscillations of the rotation speed do not occur when the load changes.
Parts of electric motor rotation controllers
In these circuits, it is possible to use the following replacements of radio components: transistor KT817B - KT815, KT805; KT117A can be replaced with KT117B-G or 2N2646; Operational amplifier K140UD7 on K140UD6, KR544UD1, TL071, TL081; timer NE555 - S555, KR1006VI1; microcircuit TL074 - TL064, TL084, LM324.
When using a more powerful load, the KT817 key transistor can be replaced with a powerful field-effect transistor, for example, IRF3905 or similar.
To perform many types of work on wood, metal or other types of materials, it is not high speeds that are required, but good traction. It would be more correct to say - the moment. It is thanks to him that the planned work can be completed efficiently and with minimal power losses. For this purpose, DC (or commutator) motors are used as a drive device, in which the supply voltage is rectified by the unit itself. Then, to achieve the required performance characteristics, it is necessary to adjust the speed of the commutator motor without loss of power.
Features of speed control
It is important to know, what each engine consumes when rotating not only active, but also reactive power. In this case, the level of reactive power will be higher, which is due to the nature of the load. In this case, the task of designing devices for regulating the rotation speed of commutator motors is to reduce the difference between active and reactive powers. Therefore, such converters will be quite complex, and it is not easy to make them yourself.
You can construct only some semblance of a regulator with your own hands, but there is no point in talking about saving power. What is power? In electrical terms, it is the current drawn multiplied by the voltage. The result will give a certain value that includes active and reactive components. To isolate only the active one, that is, to reduce losses to zero, it is necessary to change the nature of the load to active. Only semiconductor resistors have these characteristics.
Hence, it is necessary to replace the inductance with a resistor, but this is impossible, because the engine will turn into something else and obviously will not set anything in motion. The goal of lossless regulation is to maintain torque, not power: it will still change. Only a converter can cope with such a task, which will control the speed by changing the duration of the opening pulse of thyristors or power transistors.
Generalized controller circuit
An example of a controller that implements the principle of controlling a motor without power loss is a thyristor converter. These are feedback proportional integrated circuits that provide strict regulation characteristics, ranging from acceleration and braking to reverse. The most effective is pulse-phase control: the repetition rate of the unlocking pulses is synchronized with the network frequency. This allows you to maintain torque without increasing losses in the reactive component. The generalized diagram can be represented in several blocks:
- power controlled rectifier;
- rectifier control unit or pulse-phase control circuit;
- tachogenerator feedback;
- current control unit in the motor windings.
Before delving into a more precise device and principle of regulation, it is necessary to decide on the type of commutator motor. The control scheme for its performance characteristics will depend on this.
Types of commutator motors
At least two types of commutator motors are known. The first includes devices with an armature and an excitation winding on the stator. The second includes devices with an armature and permanent magnets. It is also necessary to decide, for what purpose is it necessary to design a regulator:
Motor design
Structurally, the engine from the Indesit washing machine is simple, but when designing a controller to control its speed, it is necessary to take into account the parameters. Motors may have different characteristics, which is why the control will also change. The operating mode is also taken into account, which will determine the design of the converter. Structurally, the commutator motor consists from the following components:
- An armature, it has a winding laid in the grooves of the core.
- Collector, a mechanical rectifier of alternating mains voltage, through which it is transmitted to the winding.
- Stator with field winding. It is necessary to create a constant magnetic field in which the armature will rotate.
When the current in the motor circuit, connected according to the standard circuit, increases, the field winding is connected in series with the armature. With this inclusion, we also increase the magnetic field acting on the armature, which allows us to achieve linearity of characteristics. If the field remains unchanged, then it will be more difficult to obtain good dynamics, not to mention large power losses. It is better to use such motors at low speeds, since they are more convenient to control at small discrete movements.
By organizing separate control of the excitation and armature, it is possible to achieve high positioning accuracy of the motor shaft, but the control circuit will then become significantly more complicated. Therefore, we will take a closer look at the controller, which allows you to change the rotation speed from 0 to the maximum value, but without positioning. This might come in handy, if a full-fledged drilling machine with the ability to cut threads will be made from a washing machine engine.
Scheme selection
Having found out all the conditions under which the motor will be used, you can begin to manufacture a speed controller for the commutator motor. You should start by choosing a suitable scheme that will provide you with all the necessary characteristics and capabilities. You should remember them:
- Speed regulation from 0 to maximum.
- Providing good torque at low speeds.
- Smooth speed control.
Looking at many schemes on the Internet, we can conclude that few people are creating such “units”. This is due to the complexity of the control principle, since it is necessary to organize the regulation of many parameters. Thyristor opening angle, control pulse duration, acceleration-deceleration time, torque rise rate. These functions are handled by a circuit on the controller that performs complex integral calculations and transformations. Let's consider one of the schemes, which is popular among self-taught craftsmen or those who simply want to put to good use an old motor from a washing machine.
All our criteria are met by a circuit for controlling the rotation speed of a brushed motor, assembled on a specialized TDA 1085 microcircuit. This is a completely ready-made driver for controlling motors that allow you to adjust the speed from 0 to the maximum value, ensuring torque maintenance through the use of a tachogenerator.
Design Features
The microcircuit is equipped with everything necessary for high-quality engine control in various speed modes, from braking to acceleration and rotation at maximum speed. Therefore, its use greatly simplifies the design, while simultaneously doing all universal drive, since you can choose any speed with a constant torque on the shaft and use it not only as a drive for a conveyor belt or drilling machine, but also for moving the table.
The characteristics of the microcircuit can be found on the official website. We will indicate the main features that will be required to construct the converter. These include: an integrated frequency-to-voltage conversion circuit, an acceleration generator, a soft starter, a Tacho signal processing unit, a current limiting module, etc. As you can see, the circuit is equipped with a number of protections that will ensure stable operation of the regulator in different modes.
The figure below shows a typical circuit diagram for connecting a microcircuit.
The scheme is simple, so it is quite reproducible with your own hands. There are some features that include limit values and speed control method:
If you need to organize a motor reverse, then for this you will have to supplement the circuit with a starter that will switch the direction of the excitation winding. You will also need a zero speed control circuit to give permission for reverse. Not shown in the picture.
Control principle
When the rotation speed of the motor shaft is set by a resistor in output circuit 5, a sequence of pulses is formed at the output to unlock the triac by a certain angle. The speed of rotation is monitored by a tachogenerator, which occurs in digital format. The driver converts the received pulses into an analog voltage, which is why the shaft speed is stabilized at a single value, regardless of the load. If the voltage from the tachogenerator changes, the internal regulator will increase the level of the output control signal of the triac, which will lead to an increase in speed.
The microcircuit can control two linear accelerations, allowing you to achieve the dynamics required from the engine. One of them is installed on the Ramp 6 pin of the circuit. This regulator is used by washing machine manufacturers themselves, so it has all the advantages to be used for domestic purposes. This is ensured by the presence of the following blocks:
Usage similar scheme provides full control of the commutator motor in any mode. Thanks to forced acceleration control, it is possible to achieve the required acceleration speed to a given rotation speed. Such a regulator can be used for all modern washing machine motors used for other purposes.