PWM, PWM controller. Scheme

One of the approaches used to significantly reduce heating losses of power components of radio circuits is the use of switching operating modes of installations. With such systems, the electrical power component is either open - at this time there is virtually zero voltage drop across it, or open - at this time zero current is supplied to it. Power dissipation can be calculated by multiplying current and voltage. In this mode, it is possible to achieve an efficiency of about 75-80% or more.

What is PWM?

To obtain a signal of the required shape at the output, the power switch must be opened only for a certain time, proportional to the calculated output voltage. This is the principle of pulse width modulation (PWM). Next, a signal of this shape, consisting of pulses varying in width, enters the filter area based on an inductor and a capacitor. After conversion, the output will be an almost ideal signal of the required shape.

The scope of PWM is not limited to switching stabilizers and voltage converters. Using this principle when designing a powerful audio frequency amplifier makes it possible to significantly reduce the device's energy consumption, leads to miniaturization of the circuit and optimizes the heat transfer system. The disadvantages include the mediocre quality of the output signal.

Formation of PWM signals

Creating PWM signals of the desired shape is quite difficult. However, the industry today can delight with wonderful special chips known as PWM controllers. They are inexpensive and completely solve the problem of generating a pulse-width signal. Familiarization with their typical design will help you navigate the structure of such controllers and their use.

The standard PWM controller circuit assumes the following outputs:

• Common output (GND). It is implemented in the form of a leg, which is connected to the common wire of the device’s power supply circuit.
• Power pin (VC). Responsible for power supply of the circuit. It is important not to confuse it with its neighbor with a similar name - the VCC pin.
• Power control pin (VCC). As a rule, the PWM controller chip takes over control of the power transistors (bipolar or field-effect). If the output voltage decreases, the transistors will open only partially, and not completely. Rapidly heating up, they will soon fail, unable to cope with the load. In order to exclude this possibility, it is necessary to monitor the supply voltage at the input of the microcircuit and not allow it to exceed the design mark. If the voltage at this pin drops below that set specifically for this controller, the control device turns off. Typically, this pin is connected directly to the VC pin.

Output control voltage (OUT)

The number of pins of a microcircuit is determined by its design and operating principle. It’s not always possible to immediately understand complex terms, but let’s try to highlight the essence. There are microcircuits on 2 pins that control push-pull (double-arm) cascades (examples: bridge, half-bridge, 2-stroke inverse converter). There are also analogues of PWM controllers for controlling single-ended (single-arm) cascades (examples: forward/reverse, boost/buck, inverting).

In addition, the output stage can be single- or two-cycle in structure. Push-pull is mainly used to drive a voltage dependent FET. To quickly close, it is necessary to achieve rapid discharge of the gate-source and gate-drain capacitors. For this purpose, the push-pull output stage of the controller is used, the task of which is to ensure that the output is shorted to a common cable if it is necessary to close the field-effect transistor.

PWM controllers for high-power power supplies can also have output switch controls (drivers). It is recommended to use IGBT transistors as output switches.

The main problems of PWM converters

When operating any device, it is impossible to completely eliminate the possibility of breakdown, and this also applies to converters. The complexity of the design does not matter; even the well-known TL494 PWM controller can cause operational problems. Malfunctions have a different nature - some of them can be detected by eye, while detection of others requires special measuring equipment.

To use a PWM controller, you should familiarize yourself with the list of main device malfunctions, and only later - with options for eliminating them.

Troubleshooting

One of the most common problems is breakdown of key transistors. The results can be seen not only when trying to start the device, but also when examining it with a multimeter.

In addition, there are other faults that are somewhat more difficult to detect. Before checking the PWM controller directly, you can consider the most common cases of breakdowns. For example:

• The controller stalls after starting - a break in the OS loop, a current drop, problems with the capacitor at the filter output (if any), or the driver; Perhaps the control of the PWM controller has gone wrong. It is necessary to inspect the device for chips and deformations, measure the load indicators and compare them with standard ones.
• The PWM controller does not start - one of the input voltages is missing or the device is faulty. Inspecting and measuring the output voltage can help, or, as a last resort, replacing it with a known working analogue.
• The output voltage differs from the nominal voltage - there is a problem with the OOS loop or with the controller.
• After the start, the PWM on the power supply goes into protection if there is no short circuit on the keys - incorrect operation of the PWM or drivers.
• Unstable operation of the board, the presence of strange sounds - a break in the OOS loop or RC chain, degradation of the filter capacity.

In conclusion

Universal and multifunctional PWM controllers can now be found almost everywhere. They serve not only as an integral component of power supplies for most modern devices - standard computers and other everyday devices. Based on controllers, new technologies are being developed that can significantly reduce resource consumption in many areas of human activity. Owners of private houses will benefit from battery charge controllers from photovoltaic batteries, based on the principle of pulse-width modulation of the charge current.

The high efficiency makes the development of new devices based on the PWM principle very promising. Secondary power sources are not the only area of ​​activity.

The modern power supply market offers the developer a wide selection of various electronics products, each of which, to one degree or another, is ready to solve the problems assigned to engineers. This article aims to review and help select the optimal solutions from the proposals of the most well-known players in the switching power supply market.

Introduction

Previously, power systems in the functional diagram at the design stage were very often given attention at the final stage; many experts underestimated their ability to improve the product as a whole. Recently, trends in the development of the electronics industry have brought to the forefront for developers such tasks as reducing energy consumption, weight and size characteristics, development time and the final cost of the product. Such requirements have changed the once secondary attitude towards the power supply units of the device, because in many respects the ability of the final product to be competitive and withstand stringent market requirements depends on them.

Today, the leading position in this area is traditionally occupied by Power Integration. The products of this company are well known, the application technology has been proven many times, which is the factor that tips the scales in its favor.

As competing products, consider the power supply offering from Fairchild Semiconductor. This company has long established itself in the field of power electronics, offering inexpensive, high-quality and multifunctional solutions. As a rule, the products of this manufacturer are focused on areas that require a high degree of reliability and performance.

Power supplies

Virtually all electronics products require DC power from a battery or power source. In addition, most devices have increased requirements for its quality. The voltage must be regulated and protected from ripples that occur. There are three types of power converters:

• DC\DC converter;
• AC\DC power supply;
• DC\AC inverter.

An ideal source should generate the required voltage values, despite changes in ambient temperature, load or input voltage. Moreover, it must be 100% effective. In Fig. 1 you can see the shortcomings of the real power supply.

Rice. 1. Real power supply

Today there are linear and. Pulse conversion is interesting because of its high efficiency and power density. The table compares some of the main features of linear and switching power supplies. Voltage and current stability is usually better with linear power supplies, sometimes by an order of magnitude, but switching power supplies often use linear output stabilizers that improve the output voltage parameters.

Table. Comparison of switching and linear power supplies

Finally, switching power supplies have a wider input voltage range. The input voltage range of linear power supplies usually does not exceed 10% of the rated value, which has a direct impact on efficiency. For pulsed sources, the effect of changing the input voltage on the efficiency is very small or absent altogether, and a wide operating range of input voltages makes it possible to work with large changes in the mains voltage (up to 40%). The most commonly used (due to its advantages) is the flyback converter circuit (Fig. 2). Many microcircuits for controlling these converters have been developed. There are both microassemblies that use an external power transistor, and those that include a power element in their composition, which reduces its dimensions.

Rice. 2. Diagram of a flyback converter with a matching transformer and galvanic isolation

In the recent past, the implementation of pulse width modulation and performance monitoring was carried out using discrete elements. The emergence of integrated circuits that take on these functions greatly simplified the development process and reduced the overall dimensions of power supplies several times (Fig. 3). Leaders in the production of power supply control integrated circuits are Power Integrations and Fairchild Semiconductor.

Rice. 3. Evolution of power supplies

Power Integrations Voltage Regulators

In the circuit design of modern switching power supplies (SMPS), PWM regulators, made in small-sized planar packages with six pins, have become widely popular. The housing type designation can be SOT-23-6, SOT-23-6L, SOT-26, TSOP-6, SSOT-6. The appearance and location of the pins are shown in the figure below. In this case, the left fragment of the picture shows the code marking LD7530A

Pin assignment:
1 - GND. (Common wire).
2 - FB. (FeedBack - Feedback). Input for controlling the duration of pulses using a signal from the output voltage. Sometimes may be designated COMP (input comparator).
3 - RI/RT/CT/COMP/NC - Depending on the type of microcircuit, it can be used for the frequency-setting RC circuit (RI/RT/CT), or for organizing protection, as the input of a PWM shutdown comparator at a threshold value at its input specified in the document. In some types of microcircuits this input may not be used in any way (NC - No Connect).
4 - SENSE, otherwise CS (Current Sense) - Input from the current sensor at the source of the key.
5 - VCC - Supply voltage input and start of the microcircuit.
6 - OUT (GATE) - Output for controlling the gate (Gate) of the key.

Functionally, such regulators operate on the principle of the previously popular xx384x series PWM microcircuits, which have proven themselves well in terms of reliability and stability.

Some difficulties often arise when replacing or choosing an analogue for such PWM regulators due to the use of code markings in the designation of the type of microcircuits. The situation is complicated by a large number of component manufacturers who do not always make documentation available to the masses; also, not all manufacturers of finished devices supply repair service centers with circuit diagrams, so repairmen often have to study actual circuit solutions based on installed components and wiring connections directly on the board.

In practice, PWM microcircuits are often found with marking codes EAxxx and Eaxxx. Official documentation for them is not found in the public domain, but there are discussions on forums and pieces of pictures from PDF from System General, which publishes them as SG6848T and SG6848T2. Drawing is attached.

We present to the attention of craftsmen tables compiled from information available on the Internet and PDF documents for selecting analogues when replacing the most common six-legged planar PWM with pinout: pin1 - GND, pin2 - FB (COMP), pin4 - Sense, pin5 - Vcc, pin6 - OUT .
Their main difference is the application and purpose of pin 3.

PWM controllers (PWM), without using pin 3.

PWM controllers (PWM) with a 95-100 kOhm resistor installed on pin 3.

Using the PWMs listed below, the frequency should be set with resistor RT (RI) from pin 3 to ground. Usually its nominal value is 95-100 kOhm for a frequency of 65-100 KHz. For more details, see the attached documentation. PDF files are packaged in RAR.

PWM controllers in which pin 3 is used differently.

When using the PWM controllers listed below, you should pay attention to pin 3, which can be used to organize protection - thermal or against exceeding the input voltage.
The frequency can be fixed at 65kHz, or set by the value of the capacitor at pin 3.
When replacing any microcircuits with analogues, carefully study the documentation. PDF files are packaged in RAR archive.

When we come across an unfamiliar word or concept in some literature, we want to quickly find out its definition. Knowing precise definition You can further trace the scope and methods of application of the main character of a particular concept. Today we will take a closer look at such a concept as a PWM controller.

Shima concept

Before defining the mentioned phrase, you should find out or just remind yourself of the principle of heating the power components of a radio circuit. Their essence lies in the operation of several switching modes. All electrical power components in such radio circuits are always in two states. The first is open, and the second is revealed. What is the difference between these two conditions? In the first case, the component has zero current. In the second, the component has a zero voltage value. The end result of the interaction of electrical power components with the required voltage can be considered the receipt of a signal of the form that is needed according to the established rules.

A shim is a special modulator designed to control the opening time of a power switch. The time for opening the key is set taking into account the voltage received. Get ideal option processing of a signal is possible only if the signal has passed through all the necessary stages without difficulty before being converted. What are these stages and what does the formation of such a signal consist of?

Features of the PWM controller

The process of creating shim signals is very difficult. To facilitate this process, special microcircuits were invented. It is the microcircuits involved in the formation of PWM signals that are called PWM controllers. Their existence in most cases helps to completely solve the problem with the formation of wide-pulse signals. To more easily understand the mission and significance of the shim controller, it is necessary to become familiar with the features of its structure. Today it is known that any PWM controller actively used in electronics has the following components:

• Power output. Bears great responsibility for the electrical supply of all existing circuits. Often The power pin is confused with the power control pin. It is important to know that despite the similar words in the name, these two concepts have completely different characteristics. This will once again clearly prove your familiarity with the power control pin.
• Power control pin. This component of the microcircuit monitors the state of voltage indicators directly at the pin of the microcircuit. The main task of the power control output is to prevent the design level from being exceeded. There is one serious danger, namely voltage reduction on the way out. If the voltage is reduced, the transistors begin to open halfway. Due to incomplete opening, they heat up quickly and can ultimately fail quickly. That's why moderate tension- this is the key to long-term operation of transistors in PWM controllers.
• general exit. The third main element of the scheme has the shape of a leg. This leg, in turn, is connected to the common wire of the circuit, which is responsible for powering the entire system.

All three components are very important. If at least one of the elements fails for some reason, the performance of the entire microcircuit deteriorates noticeably or stops completely.

Chip management systems

It is important to know not only what PWM controller chips are made of, but also what types of systems themselves exist. Currently, there are two main widely available pulse modulation systems in which PWM control takes an active part. Here are some of their features:

But you can get the desired signal at the output using both software and hardware methods.

Hardware method. The signal is received in this way using a special timer, which is initially built into the digital system. Such a timer generates or facilitates the inclusion of pulses at certain stages of signal output.

Software method. In this case, signals are received by executing special software commands. The software method has more options than hardware. At the same time, using this method of receiving signals can take up a lot of memory.

What can we say about the “heart of the system”. The shim controller, which is actively used in digital modulators, has its advantages. It is worth remembering the following:

• Low cost.
• Stable job.
• High reliability.
• Possibility to save energy.
• high signal conversion efficiency.

All of these advantages make the digital system more popular among consumers.

• Analog modulator. The operating principle of an analog modulator is fundamentally different from the operating principle of a digital one. The whole essence of the operation of such a modulator is to compare two signals. These signals differ in frequency order. The operational amplifier is the main element of the analog modulator, which is responsible for comparing signals. Comparison of signals is carried out at the output. The amplifier uses two signals as a comparison. The first is a high-frequency sawtooth voltage. The second signal is low frequency voltage. After comparison, rectangular pulses appear. The duration of the pulses directly depends on the modulating signal.

PWM controller in switching power supplies

Many electrical appliances today are equipped with special power supplies. These blocks help transform one type of voltage into another. IN Two devices take part in the energy conversion process:

• Switching power supply.
• analog transformer devices.

In this article we will pay more attention to the first device, since it is the one that uses the PWM controller.

Scheme of operation of a switching power supply

This device was born just a few decades ago. However, it has already become popular and in demand. Switching power supply consists of the following parts:

1. Filter condensate.
2. Key power transistor.
3. A network rectifier consisting of several elements.
4. Rectifier diodes of the output system.
5. Power chokes. The choke helps correct the resulting voltage.
6. Switching power supply. It is from here that the voltage is converted into a power circuit.
7. Output voltage control circuits.
8. Storage filter container;
9. Optocoupler;
10. Master oscillator.
11. feedback circuits.

Knowing the composition of the pulse unit, you should familiarize yourself with the principle of its operation.

Operating principle of the pulse unit

Operating principle of the pulse unit consists of delivering a stabilized supply voltage based on the principle of interaction between the elements of an inert system. Here are the step-by-step steps that clearly demonstrate the essence of the activity of such a power supply:

• Transfer of mains voltage to the rectifier (carried out using special wires).
• Using a rectifier filter, the voltage is smoothed. Capacitors also take part in this process.
• With the help of a diode input bridge, sinusoids are rectified. Next, with the participation of a transistor system, the passing sinusoids must be converted into high-frequency pulses. Often the pulses are rectangular in shape.

But the question arises, what role do PWM controllers play in the pulse unit? We will try to answer this in the next subheading.

The role of the shim controller in the operation of the pulse unit

PWM controllers play an important role in the pulse block. It is responsible for processes associated with pulse width modulation. The PWM controller promotes the generation of pulses that have the same frequency, but at the same time different switching durations. All supplied pulses correspond to a certain logical unit. The pulses not only have the same frequency, but also the same amplitude. Duration of operation of a logical unit may change during its operation. Such changes help to best manage the operation of the electronic system.

Thus, the PWM controller is one of the important chains involved in the operation of the pulse unit. In some types, in addition to the PWM controller, the successful functioning of the power supply is ensured by a pulse transformer and a special cascade of power switches.

In what areas are switching power supplies used? First of all, in electronics. This will be discussed further.

Features of the chip or how a laptop can work

Computer power supply and the role of the PWM controller in it All modern computers, including laptops, are equipped with switching power supplies. The units installed in a laptop or a regular computer contain an individual PWM controller chip. The standard chip is considered to be the TL494CN chip.

First of all, it is worth mentioning the main task of the TL494CN chip. So, the main task of the circuit is pulse width modulation. In other words, the microcircuit produces voltage pulses. Some pulses are adjustable, others are not. The microcircuit provides approximately 6 ways to output signals. Let us mention some interesting details of each pin of the laptop chip.

First conclusion. Considered to be the positive input of the error signal amplifier. The voltage level at the first pin has a significant impact on the operation of subsequent pins. If the voltage at the second pin is low, the error amplifier output will have low readings. On the contrary, at increased voltage error amplifier performance will increase.

Second conclusion. The second pin is, on the contrary, a negative output for the amplifier. Here, voltage indicators have a slightly different effect on the amplifier. So, at high voltage (higher than at the first pin), the amplifier output has low performance. In the case of low voltage, the amplifier has high data.

Third conclusion. Serves as a kind of contact point. Changes in voltage level depend on the two diodes equipped with the internal amplifier. When the signal level changes on at least one diode, the voltage level of the entire amplifier changes. In some cases, the third pin provides the rate of change of pulse width.

Fourth conclusion. Capable of controlling the duty cycle range of all output pulses. The level of incoming voltage in the fourth pin affects the width of the pulses in the PWM controller chip.

Fifth conclusion. The fifth conclusion faces a slightly different task. It connects the lead-up capacitor to a given microcircuit. The capacity of the connected condensate has a significant impact on the frequency of the output pulses of the PWM controller.

Sixth conclusion. Serves to connect a timing register, which also affects the frequency.

All these six pins contribute to the fulfillment of the main task assigned to the PWM controller microcircuit - the output of pulses with wide modulation. And this action, in turn, affects the operation of the pulse unit, and therefore the operation of the laptop.

If the shim - the controller fails

At times, PWM circuit controllers and the power supply (including those built into the laptop) can break down and fail. In such cases, you will need to identify faults (in some cases it is necessary to check the power source, in others it is worth checking the circuit itself). Multimeters were developed for this purpose. Multimeters carefully examine performance Shim - controllers and, if necessary, help eliminate malfunctions. The most common reasons why these devices should be checked are unstable operation of the board and changes in voltage readings. If you eliminate them, the technique will work.

In certain conditions it is necessary to install autonomous power supply systems. An integral part of them are modules with rechargeable batteries. Such units can be charged from various power sources, which do not always provide stable input parameters.

The optimal situation in such conditions is to use devices or elements that can take control of this charging process. In such a case, the main role is played by the PWM controller in the circuit.

Active Processes

These controllers are most often used to work with alternative energy sources, which include:

• wind turbines;
• modules with solar panels;
• blocks with hydraulic turbines;
• diesel power supplies.

This makes them popular in modern homes and businesses.

In the global scientific community, PWM stands for pulse-width modulation (PWM), which in translation means pulse-width modulation. In fact, this is an operation of controlling the power approaching the consumer by correcting the duty cycle of pulses with a constant frequency.

There are several types of PWM power controller:

• digital;
• analog;
• with two levels;
• with three levels.

VIDEO: Operating principle of the UC3843 PWM controller in a switching power supply

Installation required

Controllers are required for circuits that contain lead-acid batteries. This is due to the fact that such batteries negatively perceive both overcharging and significant discharge. In the first case, rapid failure of the battery may occur due to boiling of the electrolyte or even explosion of cans with it. In the second case, the process leads to the destruction of the plates.

The PWM controller also helps alkaline batteries by blocking their overcharging. This element breaks the circuit, disconnecting the load from the power source.

PWM elements are often built into switching power supplies or uninterruptible power supplies. They are also found in inverters.

Typically, disconnection occurs when a twelve-volt battery reaches a level of 10.5 or 11 V. In this case, after 10 hours of continuous operation, the capacity drop will be from 100% to approximately 20%. In the process of faster discharge, the capacity will decrease.

Under certain conditions, it is possible to adjust the shutdown voltage during the manufacturing or tuning process. However, what dominates the shelves is not the voltage regulator, but a device with a standard level of output parameters.

You should not skimp on high-quality equipment for your own solar or wind power station; we recommend purchasing exclusively branded equipment with a long service life.

The table will help you navigate the costs:

Based on the cost proportions, it is obvious that PWM elements are not a large cost item in the circuit. At the same time, they play an important role in ensuring the efficiency of the system, extending the life of the remaining equipment.

Types of controllers

Several types of such elements are common in photovoltaic circuits. They are differentiated not only by cost, but also by operating algorithms, methods of setting current parameters, etc.

The simplest ones in design simply break the circuit and block the source from it when a certain voltage is reached, for example, a level of 14.4 V. When it drops to a level of 12-13 V, the power supply again assembles the circuit for charging. In this cycle, the battery charge level is approximately 60%. Stable undercharging leads to the formation of sulfation on the lead plates and soon failure of the power source.

This type is practically not mass-produced, but is found among homemade craftsmen. They produce elements for savings at bargain prices, although in the end the savings turn out to be an illusion due to the imminent breakdown of the battery.

PWM regulators are a more advanced technology and allow you to recharge the battery up to 100%. The process involves several stages of battery charging:

• the maximum current is supplied to the terminals, which allows the battery to consume all of it supplied from the sun to the modules at a given minute;
• with a PWM charge, the voltage level reaches the set parameter and the parameter is constantly maintained in order to avoid gas formation in the banks (the current slowly decreases);
• equalization occurs, because for most batteries it is natural to receive a charge to the level of gas formation when the voltage on all containers with electrolyte is equalized (the plates are cleaned and the liquid inside is mixed);
• stabilization and gradual reduction of voltage is carried out when the battery receives a full charge, preventing overheating.

Manufacturers offer their controllers even with special informative elements:

• light indication;
• liquid crystal screens;
• multifunctional monitors.

In certain models there is functionality that allows you to determine the battery charge level. With this option, you can customize the operation for a specific battery, prolonging its service life.

For some products, there is an indication in the certificate that it is possible to indicate the charge level in % (state of charge SOC), but this option does not always work correctly.

To monitor SOC as reliably as possible, it is necessary to monitor several battery charging cycles and carry out independent calculations using rather cumbersome formulas.

Popular brands

In budget models, percentages are indicated approximately. This applies to EPSolar brand models. Manufacturers from Morningstar have completely abandoned SOC and provide information to the user about the battery voltage in volts. Percentage readings from the following brands are considered more reliable:

• Steca PR1010-3030;
• Tarom;
• Power Tarom.

Chinese manufacturers of EPSolar are the most popular in the market for this electronics. Their products are optimal in terms of cost and quality, while their arsenal includes models that have absorbed the maximum amount of functionality. The high quality of components and assembly distinguishes the brand from competitors such as Steca Solar. There are models with timers for turning off/on different night lights.

The German brand Steca is more expensive. European quality is tied to the value of the currency, so not everyone can choose such models.

Choosing the right controller

During the selection process, you should pay attention to the input parameters. It is regulated by manufacturers. The parameter is indicated in the technical data of the device. This value must correspond to the XX voltage of the battery or the sum of the XX voltages of several solar units in a series connection. It is recommended to add a 20% margin.

The total design power of the battery is selected to be no more than the multiplied value of the system voltage and output current. In this case, we also set a margin of 20%. If it is not possible to carry out calculations yourself, then you should contact specialists in electrical engineering.

VIDEO: How to test any PWM (PWM) controller