This section provides an overview for pwms as well as their applications and principles. Also, please take a look at the list of 6 pwm manufacturers and their company rankings.
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A PWM stands for "pulse width modulation" and is a technology for generating pulse waves of various widths. Pulse waves are digital signals, but by combining various pulse waves, they can be converted into various pseudo-analog signals, including sine waves.
A PWM is a technology that modulates the pulse width with a fixed period. There is also a PFM technology that modulates the frequency with a constant pulse width, but both are used for switching between energized and de-energized.
PWMs are used to control the voltage of power supplies and to control the energizing and de-energizing cycles of semiconductors. In particular, it is often used to control DC motors efficiently. By controlling the time of voltage application to the motor, it is possible to control the running voltage.
In addition, when generating modulated AC current in an inverter circuit, PWMs can be used to generate pulse voltages with various widths, which can then be synthesized to perform DC-AC conversion. PWMs are used not only in inverter circuits but also in controlling switching power supplies and dimming LEDs without affecting the light color.
PWMs circuit, which perform pulse width modulation, use transistors to generate pulse waves of various widths by repeatedly switching the circuit on and off.
PWMs modulate the pulse width over a fixed period, so the duty cycle is varied. Duty cycle is the pulse width divided by the period, expressed in "% (percentage)." In voltage control, the running voltage is the product of the pulse voltage and duty cycle, and a duty cycle of 100% is the same as when a DC power supply is used.
When voltage control is performed using PWMs, the power supply is turned off for a period, which makes it more power efficient than using a DC power supply that works steadily. In addition, in digital circuits such as microcontrollers, pseudo-analog signals can be generated simply by synthesizing pulse waves, making it possible to construct analog conversion circuits composed entirely of digital circuits without the use of D/A converters or other devices.
When dynamically controlling a load with an electronic circuit, there are two methods: one is to control the load with a constant voltage and the other is to control the load with a constant current, and the other is to control the load with PWMs.
Recently, more energy-efficient methods have become the trend due to environmental and energy issues. The reasons for the low efficiency of linear methods, such as constant voltage control and constant current control, are as follows.
For example, if a regulated power supply with a maximum voltage of 10 V and current capacity of 2 A is used at 5 V 2 A, the power loss consumed in the power supply circuit is (12 V - 5 V) x 2 A = 14 W when the input voltage of the power supply is 12 V. The power consumed in the load is 5 V x 2 A = 10 W.
The power consumed by the load is 5V x 2A = 10W. 1.4 times the power consumed by the load is consumed as a loss in the circuit. This is not only wasteful power consumption but also increases the cost, size, and weight of the circuit due to the large number of components used.
On the other hand, PWMs control does not change the output voltage, but varies the pulse width according to the output. For example, with PWMs at 10 V and a duty ratio of 50%, the apparent drive voltage is 5 V, which means that there is no theoretical loss and the actual efficiency is very high.
In PWMs control, the term duty ratio is often used. In a PWMs waveform with a duty ratio of 50%, the H and L pulses are the same width.
Changing the duty ratio changes the apparent voltage. For example, when the duty ratio is changed from 0% to 25% to 50% to 75% to 100% with 10V PWMs, the apparent voltage to the load changes from 0V to 2.5V to 5V to 7.5V to 10V.
Although a microcontroller requires a D/A converter to output an analog signal, it is possible to create a pseudo analog signal by using PWMs, which has a moderate switching frequency and a programmable duty ratio. In this case, it is possible to generate an appropriate analog signal up to the digital signal level at the I/O pins.
In this case, an appropriate LPF must be inserted in the I/O pin to remove the PWMs switching frequency component and its harmonic components.
As mentioned above, PWMs control is often used to control motor operation and to increase the efficiency of inverters. This generates noise at various switching frequencies, which range from 30 to 40 Hz.
This frequency is approximately 30 to 40 MHz, which not only causes noise problems for the surrounding people and environment but also affects AM radios and sensors that use low frequency bands. Therefore, some sort of noise countermeasure is often required. Specific measures include, in the case of inverter equipment, covering the equipment with a housing, shortening the power cable, and inserting noise filters such as ferrites or LC chokes.
In some cases, PWMs control allows the user to change this switching frequency, so it is another option to try. Lowering the switching carrier frequency reduces the overall switching noise itself, but generally increases the noise of the motor.
There are examples of products that reduce motor-specific generated noise by employing a modulation method that actively distributes the switching carrier frequency from low to high frequencies.
*Including some distributors, etc.
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