In the world of modern electronics and circuit design, you can often hear the mysterious abbreviation PWM. For a beginner, this may seem like a complex term from higher mathematics or quantum physics, but in reality everything is much simpler. PWM is Pulse Width Modulation, a method of controlling the power supplied to a load by varying the duration of pulses at a constant frequency.
Imagine an ordinary light switch that you flip at incredible speed, turning the light bulb on and off. If you do this quickly enough, the human eye will not notice the flickering, and the lamp will burn evenly, but with less brightness. It is this principle that underlies Pulse Width Modulation (PWM), as it is called internationally.
Understanding what shim means in electronics is critical not only for engineers developing devices, but also for ordinary users. The quality of implementation of this method determines whether your eyes will hurt from the monitor, how efficiently the fan motor will work, and even how long your smartphone’s battery will last.
The physical principle of operation of pulse width modulation
The method is based on the use of rectangular pulses. The key parameter here is duty cycle or duty cycle (Duty Cycle). This is the ratio of the time when the signal is in the active state (logical one) to the period of complete oscillation.
If we imagine an oscillogram, we will see alternating high and low voltage levels. By changing the width of the “high” rectangle, we change the average voltage value over the period. At the same time, the pulse amplitude remains unchanged, which makes the method very effective.
The repetition rate of these pulses also plays a huge role. In power electronics it can be several kilohertz, while in audio technology or LED control it reaches tens and hundreds of kilohertz. The higher the frequency, the easier it is to filter out ripple in the output.
⚠️ Attention: Low PWM frequency (less than 200-300 Hz) can cause noticeable flicker, which, although not always visible to the eye, can lead to fatigue and headaches.
There are several types of modulation, but in household appliances the most common type is pulse width. It allows you to transmit analog signals over digital communication channels and effectively manage powerful loads.
Where is PWM used in modern technology?
The scope of application of the technology is incredibly wide. Almost any device that requires smooth adjustment of power or speed uses this principle. This is not just a theoretical concept, but a daily reality.
In computer technology PWM used to control the rotation speed of cooling fans. The processor itself decides how much “air” it needs right now and sends the corresponding signal to the cooler controller.
In Class D audio devices, amplifiers operate exclusively in pulse mode. This allows you to achieve colossal efficiency (more than 90%) with minimal heat generation, which is critical for portable acoustics.
List of main applications:
- 💡 Adjusting the brightness of smartphones, TVs and monitors (LED backlighting).
- 🚗 Control of electric motors in electric vehicles and hybrid systems.
- 🔋 Chargers and voltage converters (DC-DC converters).
- 🎛️ Servo drives in robotics and automation systems.
A special place is occupied by battery charging. Smart power controllers use sophisticated PWM-based algorithms to quickly and safely charge lithium-ion batteries without overheating them.
PWM in display backlight systems
For most users, their acquaintance with the term began with a discussion of smartphone screens and monitors. In OLED and some IPS matrices, the brightness is adjusted precisely by changing the duty cycle of the backlight pulses.
When you turn the brightness on your phone down to minimum, the pulse frequency may drop and the duty cycle may become very small. The screen actually flashes quickly. For many people this goes unnoticed, but sensitive users immediately feel discomfort.
There is a concept DC Dimming is an alternative method of adjusting brightness by changing the voltage rather than the pulse frequency. It is free of flicker, but can distort color reproduction at low brightness levels.
| Parameter | PWM (PWM) | DC Dimming |
|---|---|---|
| Operating principle | Changing the pulse duration | Voltage change |
| Effect on color | Color rendering is stable | Possible distortion at minimum |
| Effect on the eyes | Possible fatigue at low frequencies | Safe for eyesight |
| Energy efficiency | High | Average |
⚠️ Attention: If you feel pain in your eyes when using your smartphone in the dark, try increasing the screen brightness or turning on eye protection mode, if available in the settings.
Modern flagship smartphones often use hybrid systems. At high brightness, PWM works at a high frequency, and at low brightness, it switches to DC Dimming or high-frequency PWM (thousands of Hertz), which is already safe.
How to check your screen for PWM?
Take the camera of another smartphone, point it at the screen of the device you are testing and reduce the brightness to minimum. If there are dark stripes on the camera screen, PWM is present. The wider the bands and the slower they move, the lower the frequency and the more harmful it is to the eyes.
Advantages and disadvantages of pulse control
Why did engineers around the world choose this method? The answer lies in efficiency. Linear power regulators, which eliminate excess voltage by turning it into heat, are irrevocably a thing of the past where savings are important.
Efficiency pulse converters reaches 95-98%. This means that almost all the energy goes towards doing useful work rather than heating the surrounding air. This allows the devices to be made compact and lightweight.
However, there is a downside to the coin. Pulse processes generate electromagnetic interference. If the device is poorly assembled, it can produce noise in the radio range and affect the operation of sensitive audio equipment.
Main advantages of the technology:
- 📉 Minimal heat dissipation (no need for huge radiators).
- ⚖️ Possibility of precise and smooth adjustment of parameters.
- 💰 Cheap components and ease of implementation in microcircuits.
The disadvantages include the difficulty of filtering the output signal and those very high-frequency interferences. Additionally, the flicker mentioned above is a significant ergonomic drawback for some users.
When choosing a power supply for an audio system, always pay attention to the ripple level. Cheap PWM blocks can add unpleasant background to the sound of speakers.
The effect of low-frequency PWM on human health
The safety issue of using devices with low-frequency modulation is acute. Although there is no direct proven connection with serious diseases, the subjective feelings of users cannot be ignored.
The human eye is capable of perceiving changes in light up to a certain frequency (critical frequency of flicker fusion). However, even if you do not see flicker, the pupil may reflexively try to adapt to the changing light flux, which causes overstrain of the eye muscles.
This leads to symptoms known as "computer vision syndrome": dryness, redness, headache and decreased concentration. This is especially noticeable when working in low light conditions.
Experts recommend paying attention to the parameter Flicker Free when purchasing monitors. This marking means that the manufacturer used a flicker-free circuit or a very high PWM frequency that is safe for eyesight.
For long-term work with text and code, choose monitors labeled Flicker-Free or DC Dimming to maintain eye health for years to come.
Technical features and frequency ranges
Different electronics industries consider different frequencies to be “safe” or “working.” In power electronics where high currents are switched, frequencies can be kept relatively low (20-100 kHz) to reduce switching losses.
In audio engineering, the PWM frequency goes into the ultrasonic range (300-500 kHz and above) in order to easily filter out the carrier frequency and leave only pure sound. Here the requirements for the quality of filtration components are very high.
For screens, the situation is as follows: frequencies below 200 Hz are considered harmful. Frequency 240 Hz and higher (standard TÜV Rheinland) is already considered safe for most users, since flickering is no longer perceived by the nervous system.
Engineers are constantly seeking the balance between frequency and efficiency. Increasing the frequency makes it possible to reduce the dimensions of transformers and capacitors, but increases the switching losses of transistors and the level of radiated interference.
☑️ What to look for when choosing a monitor
Comparison of analog and digital control
Traditional analog regulation (linear) involves the use of a variable resistor or linear stabilizer. The voltage is simply “cut off” or extinguished. This is a simple but wasteful method.
Digital PWM control allows you to transmit a control signal over one line, encoding information in pulse duration. This is the foundation for controlling modern microcontrollers and complex automation systems.
In analog circuits, the signal is subject to noise and interference. A digital PWM signal is much more resistant to interference, since the receiver only cares about the presence or absence of a pulse at a certain point in time, and not its exact amplitude.
However, to obtain pure constant current or voltage at the output of a PWM circuit, quality inductors and capacitors are required. Without them, the output will not be a straight line, but a “saw”, which can be critical for sensitive electronics.
⚠️ Attention: When assembling PWM power regulators yourself, follow the electrical safety rules. Working with high voltages and currents requires qualification and insulation.
Prospects for the development of modulation technologies
Technologies do not stand still. Classical PWM is being replaced by more complex methods, such as pulse frequency modulation (PFM) and their combinations. This allows you to further increase efficiency in specific operating modes.
LED lighting is implementing standards to ensure there is no visible or invisible flicker. Consumers are becoming more educated and demanding quality products, which is forcing manufacturers to abandon cheap, low-efficiency solutions.
The development of wide-gap semiconductors (silicon carbide, gallium nitride) makes it possible to raise the operating frequencies of converters to megahertz values. This paves the way for the creation of ultra-compact power supplies with hundreds of watts of power, the size of a credit card.
Understanding the principles of electronics operation helps not only in choosing equipment, but also in proper operation. By knowing how your device works, you can extend its life and protect your own health.
Is PWM harmful for all people?
No, sensitivity is individual. About 10-15% of the population is particularly susceptible to flicker, even at high frequencies. Others may not notice the effect for years, but eye fatigue can accumulate unnoticed.
Is it possible to remove PWM programmatically?
In most cases, no, since this is a hardware feature of the backlight control circuit. However, on some Android smartphones there are root rights and special modules that switch the control to DC Dimming mode.
Why do cheap LED lamps often flicker?
Manufacturers save on smoothing capacitors in the power driver. As a result, the current sinusoid is not leveled out, and the lamp flashes 100 times per second (in time with the mains frequency of 50 Hz), which is very harmful to vision.