PWM converter with current stabilization. Switching voltage stabilizer - the principle of operation of the stabilizer. What is pulse width modulation

The principle of pulse-width modeling (PWM) has been known for a long time, but it began to be used in various circuits relatively recently. It is a key point for the operation of many devices used in various fields: uninterruptible power supplies of various powers, frequency converters, voltage, current or speed control systems, laboratory frequency converters, etc. It has proven itself excellently in the automotive industry and in production as an element for controlling the operation of both service and powerful electric motors. The PWM regulator has proven itself when working in various circuits.

Let's look at some practical examples showing how you can regulate the speed of an electric motor using electronic circuits that include a PWM controller. Let's assume that you need to change the speed of the electric motor in the heating system of your car. Quite a useful improvement, isn't it? Especially in the off-season, when you want to regulate the temperature in the cabin smoothly. The DC motor installed in this system allows you to change the speed, but it is necessary to influence its EMF. With the help of modern electronic elements this task can be easily accomplished. To do this, a powerful field-effect transistor is switched on in the engine. It is controlled by, as you may have guessed, PWM. With its help, you can change the speed of the electric motor within a wide range.

How does a PWM regulator work in circuits? In this case, a slightly different control scheme is used, but the operating principle remains the same. As an example, we can consider the operation of a frequency converter. Such devices are widely used in production to regulate the speed of motors. To begin with, the three-phase voltage is rectified using a Larionov bridge and partially smoothed out. And only after that it is fed to a powerful bipolar assembly or module based on field-effect transistors. It is controlled by a microcontroller-based device. It generates control pulses, their width and frequency necessary to generate a certain speed of the electric motor.

Unfortunately, in addition to good performance characteristics, circuits that use a PWM controller usually experience strong noise in the power circuit. This is due to the presence of inductance in the windings of electric motors and the line itself. They combat this with a wide variety of circuit solutions: install powerful surge protectors in AC circuits or install a freewheeling diode in parallel with the motor in DC power supply circuits.

Such circuits are characterized by fairly high operational reliability and are innovative in the field of controlling electric drives of various powers. They are quite compact and well controlled. The latest modifications of such devices are widely used in production.

Presented to your attention is a circuit assembled on the basis of the NE 555 timer (domestic analogue of KR1006VI1).

Rice. 1 PWM voltage stabilizer circuit

The schematic diagram of the stabilizer is shown in Fig.1. Generator on DA1 ( NE 555), similar to that described in, works on the phase-pulse principle, because The pulse width remains unchanged and equal to hundreds of microseconds, and only the distance between the two pulses (phase) changes. Due to the low current consumption of the microcircuit (5...10 mA), I increased the resistance of R4 almost 5 times, which made its thermal regime easier. The key stage on VT2, VT1 is assembled according to the “common emitter - common collector” circuit, which minimized the voltage drop on VT1. The power amplifier uses only 2 transistors, because the high output current of the microcircuit (according to 200 mA) allows you to directly control powerful transistors without an emitter follower. Resistor R5 is necessary to exclude through current through the emitter-base transitions VT1 and collector-

Fig.2

emitter VT2, which for open transistors are connected as two diodes. Due to the relatively low speed of this circuit, it was necessary to lower the frequency of the generator (increasing the capacitance of C1). The input voltage should be the maximum possible, but not exceed 40...50 V. The resistance of resistor R8 can be calculated using the formula

So, if the input voltage is 40 V, and at the output it should vary within 0...25 V, then the resistance R8 is approximately 6 kOhm. The most significant disadvantage of switching stabilizers compared to linear ones is that due to the pulse mode of operation, a high ripple coefficient (“whistle”) is observed at the output, which is very difficult to eliminate. It is advisable to include another similar filter in series with filter L1-C3.

The most significant advantage of this circuit is its high efficiency, and with a load current of up to 200 mA, a radiator on VT1 is not needed. A drawing of the stabilizer printed circuit board is shown on Fig.2. The board is attached to the radiator using the VT1 transistor soldered to it, but it can be attached to the chassis separately from the transistor. The length of the connecting wires in this case should not exceed 10...15 cm. Resistor R7

Imported, variable; instead, you can use a trimmer or variable, which is located outside the board. The length of the wires in this case is not critical. Choke L1 is wound on a ring with an outer diameter of 10...15 mm with wire d=0.6...0.8 mm until filled, the choke of the additional filter is wound with the same wire on a coil from the transformer, the number of turns should be maximum. Transistor VT2 - any average power (KT602, KT817B...G).
Capacitor C1 is better than film (with low leakage). It is advisable to fill the L1 throttle with paraffin, because it whistles quite loudly.

A. KOLDUNOV

The use of various types of technology in everyday life is an indispensable attribute of modern society. But not all devices are designed to connect to a standard 220V power supply. Many of them consume energy with voltages ranging from 1 to 25V. To supply it, special equipment is used.

However, its main task is not so much to reduce the output parameters, but to maintain their stable level in the network. This can be solved using a stabilization device. But as a rule, such devices are quite cumbersome and not very convenient to use. The best option is a switching voltage stabilizer. It differs from linear ones not only in dimensions, but also in its operating principle.

What is a pulse stabilizer

A device consisting of two main components:

Integrating;
Adjustments.

At the first stage, energy is accumulated and then released. The control unit supplies current and, if necessary, interrupts this process. Moreover, unlike linear models, in pulsed models this element can be in a closed or open state. In other words, it works like a key.

Pulse device device

The scope of application of such devices is quite wide. However, they are most often used in navigation equipment, and a pulse stabilizer should be purchased to connect:

LCD TVs
Power supplies used in digital systems;
Low-voltage industrial equipment.

Pulse boost voltage stabilizers can also be used in networks with alternating current to convert it to direct current. Devices of this class are also used as power sources for high-power LEDs and recharging batteries.

How the equipment works

The operating principle of the device is as follows. When the regulating element is closed, energy is accumulated in the integrating element. This causes an increase in voltage. When the switch is opened, electricity is gradually transferred to consumers, leading to a decrease in voltage.

Watch the video and see how the device works:

Such a simple way of operating the device allows you to save energy, and in addition made it possible to create a miniature unit.

The following parts can be used as a regulatory element:

Thyristor;
Transistors.

The integrating units of the device are:

Throttle;
Battery;
Capacitor.

The design features of the stabilizer are related to the way it works. There are two types of devices:

With a Schmitt trigger.

Let's look at the differences between these two types of pulse voltage stabilizers.

PWM models

PWM model

Devices of this type have some differences in design. They consist of two main elements, as well as:

Generator;
Modulator;
Amplifier.

Their work is directly dependent on the input voltage, as well as the duty cycle of the pulses.

When the key is opened, energy is transferred to the load and the amplifier is switched on. It compares the voltage values and, having determined the difference between them, transmits the gain to the modulator.

The final pulses must have a duty cycle deviation that is proportional to the output parameters. After all, the position of the key depends on them. At specific duty cycle values, it opens or closes. Since impulses play the main role in the operation of the device, they gave it its name.

Devices with a Schmitt trigger

This type of pulse voltage stabilizer is characterized by a minimal set of elements. The main role in it is given to the trigger, which includes a comparator. The task of this element is to compare the output voltage value with the maximum permissible.

Let's watch a video of the operating principle of a device with a Schmitt trigger:

The operation of the device is as follows. When the maximum voltage is exceeded, the trigger switches to the zero position and opens the key. At the same time, the throttle discharges. But as soon as the voltage reaches a minimum value, it switches from 0 to 1. This leads to the closure of the switch and the flow of current into the integrator.

Although such devices have a fairly simple design, they can only be used in certain areas. This is explained by the fact that pulse voltage stabilizers can be step-down or step-up.

Classification of devices

The division of devices into types is carried out according to various criteria. So, based on the ratio of voltage at the input and output, the following types of devices are distinguished:

Inverting;
Randomly changing voltage.

The following parts can be used as a key:

Transistors;
Thyristors.

In addition, there are differences in the operation of pulsed DC voltage stabilizers. Based on this, they are classified into models operating on:

Based on pulse width modulation;
Two-position.

Advantages and disadvantages of stabilizers

Modular stabilizer

Like any other device, a modular stabilizer is not ideal. It has its pros and cons that you should be aware of. The advantages of the device include:

Easy to achieve stabilization;
High efficiency;
Voltage equalization over a wide range;
Stable output parameters;
Compact dimensions;
Soft start.

The disadvantages of the device include, first of all, its complex design. The presence of a large number of specific elements in it does not allow achieving high reliability. In addition, the disadvantage of a pulsed DC voltage stabilizer is:

Creation of a large number of frequency interference;
Difficulty in performing repair work;
The need to use devices that compensate for power factor.

Allowable frequency range

Operation of this device is possible at a sufficiently high conversion frequency, which is its main difference from devices with a network transformer. Increasing this parameter allowed us to achieve minimal dimensions.

For most models, the frequency range can be from 20 to 80 kHz. However, when choosing both key and PWM devices, you need to take into account the higher harmonics of the currents. In this case, the upper value of the parameter has certain restrictions that meet the requirements for radio frequency equipment.

Application of devices in AC networks

Devices of this class are capable of converting direct current at the input into the same at the output. If you plan to use them in an alternating current network, you will need to install a rectifier and a smoothing filter.

However, you should know that as the voltage at the input of the device increases, the output current decreases and vice versa.

Possible using a bridge rectifier. But in this case it will be a source of odd harmonics and the use of a capacitor will be required to achieve the required power factor.

Review of manufacturers

When choosing a stabilizer, pay attention not only to its technical characteristics, but also to its design features. The brand of the manufacturer is also important. It is unlikely that a device manufactured by a company unknown to a wide range of buyers will be of high quality.

Smartmodule products

Therefore, most consumers prefer to choose models belonging to popular brands, such as:

Hobbywing;
Smartmodule.

The products of these companies are of high quality, reliable and designed for a long service life.

Conclusion

The use of household appliances and other electrical appliances has become an essential condition for a comfortable life. But in order to ensure that your devices do not fail during unstable power grids, you should think in advance about purchasing a stabilizer. Which model to choose depends on the parameters of the equipment used. If you plan to connect modern LCD TVs, monitors and similar devices, then the ideal option is a switching stabilizer.

Every radio amateur is familiar with the NE555 microcircuit (analogous to KR1006). Its versatility allows you to design a wide variety of homemade products: from a simple single-vibrator pulse with two elements in the harness to a multi-component modulator. This article will discuss the circuit for switching on a timer in the mode of a rectangular pulse generator with pulse-width adjustment.

Scheme and principle of its operation

With the development of high-power LEDs, NE555 again entered the arena as a dimmer, recalling its undeniable advantages. Devices based on it do not require deep knowledge of electronics, are assembled quickly and work reliably.

It is known that the brightness of an LED can be controlled in two ways: analog and pulse. The first method involves changing the amplitude value of the direct current through the LED. This method has one significant drawback - low efficiency. The second method involves changing the pulse width (duty factor) of the current with a frequency from 200 Hz to several kilohertz. At such frequencies, the flickering of LEDs is invisible to the human eye. The circuit of a PWM regulator with a powerful output transistor is shown in the figure. It is capable of operating from 4.5 to 18 V, which indicates the ability to control the brightness of both one powerful LED and an entire LED strip. The brightness adjustment range ranges from 5 to 95%. The device is a modified version of a rectangular pulse generator. The frequency of these pulses depends on the capacitance C1 and resistances R1, R2 and is determined by the formula: f=1/(ln2*(R1+2*R2)*C1), Hz

The operating principle of the electronic brightness control is as follows. At the moment the supply voltage is applied, the capacitor begins to charge through the circuit: +Usupply – R2 – VD1 –R1 –C1 – -Usupply. As soon as the voltage on it reaches the level of 2/3U, the internal timer transistor will open and the discharge process will begin. The discharge begins from the top plate C1 and further along the circuit: R1 – VD2 –7 IC pin – -U supply. Having reached the 1/3U mark, the timer power transistor will close and C1 will again begin to gain capacity. Subsequently, the process is repeated cyclically, forming rectangular pulses at pin 3.

Changing the resistance of the trimming resistor leads to a decrease (increase) in the pulse time at the timer output (pin 3), and as a result, the average value of the output signal decreases (increases). The generated sequence of pulses is supplied through the current-limiting resistor R3 to the gate VT1, which is connected according to a circuit with a common source. The load in the form of an LED strip or sequentially connected high-power LEDs is connected to the open drain circuit VT1.

In this case, a powerful MOSFET transistor with a maximum drain current of 13A is installed. This allows you to control the glow of an LED strip several meters long. But the transistor may require a heat sink.

Blocking capacitor C2 eliminates the influence of interference that may occur along the power circuit when the timer is switched. The value of its capacitance can be any within the range of 0.01-0.1 µF.

Board and assembly parts of the brightness control

The single-sided printed circuit board has dimensions of 22x24 mm. As you can see from the picture, there is nothing superfluous on it that could raise questions.

After assembly, the PWM dimmer circuit does not require adjustment, and the printed circuit board is easy to make with your own hands. The board, in addition to the tuning resistor, uses SMD elements.

DA1 – IC NE555;
VT1 – field effect transistor IRF7413;
VD1,VD2 – 1N4007;
R1 – 50 kOhm, trim;
R2, R3 – 1 kOhm;
C1 – 0.1 µF;
C2 – 0.01 µF.

Transistor VT1 should be selected depending on the load power. For example, to change the brightness of a one-watt LED, a bipolar transistor with a maximum permissible collector current of 500 mA will be sufficient.

The brightness of the LED strip must be controlled from a +12 V voltage source and match its supply voltage. Ideally, the regulator should be powered by a stabilized power supply specifically designed for tape.

The load in the form of individual high-power LEDs is powered differently. In this case, the dimmer's power source is a current stabilizer (also called an LED driver). Its rated output current must match the current of the LEDs connected in series.