PWM


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PWM

pulse width modulation
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PWM

(Pulse Width Modulation) A modulation technique that generates variable-width pulses to represent the amplitude of an analog input signal. Like its fixed-width pulse density modulation (PDM) cousin, the output switching transistor is on more of the time for a high-amplitude signal and off more of the time for a low-amplitude signal. The digital nature (fully on or off) of the PWM circuit is less costly to fabricate than an analog circuit that does not drift over time. See PDM.

Power Supplies, Motors and Bulbs
PWM is widely used in the common "switch-mode" power supplies that convert AC power to DC for computers and other electronic devices. It is also used to control the speed of a DC motor and the brightness of a bulb. For example, if the line were closed for 1ms, opened for 1ms and continuously repeated, the target would receive an average of 50% of the voltage and run at half speed or half brightness. If the line were closed for 1ms and open for 3ms, the target would receive an average of 25%.

Audio Amplifiers and LCD Screens
PWM is used in audio amplifiers to generate output signals for cellphone speakers to high-power stereo systems. Due to the fully on/off nature of the PWM output, PWM amplifiers produce less heat than traditional analog amplifiers. See Class D amplifier.

In concert with amplitude modulation, PWM is used to deliver the required intensity to the liquid crystals in the pixels of an LCD panel. See LCD.
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References in periodicals archive ?
Therefore, the selection of PWM or SFM mode is dependent on the sensing current and output [ER.sub.o].
For the first time, expressions were obtained for determining the pulsation factors of the automatic control system of interfering harmonics of a semiconductor converter with a two-way PWM for different values of the damping coefficient and the controlled parameter.
The reality is that switching losses are less than proportional to current, but that the DC link voltage is also typically 15% reduced, so that at least a factor 3-4 reduction occurs in switching loss compared to a 60[degrees] bus clamped PWM and 4-8 compared to a centered PWM.
Diagram of the double update PWM method for the deadbeat current controller is shown in Figure 2, including the double closed-loop control and double update PWM.
Value increment (I) signifies PWM outputs' increase or decrease coefficient.
Valve hit and hold specifications Specification Valve A Valve B (FKM, Silicone Seal) Hit Voltage Level Rated Voltage Rated Voltage Minimum Hit Time 50 ms 20 ms Maximum Hit Time 20 Sec N/A Hold (PWM) 5 kHz Min., 15 kHz 5 kHz Min., 15 kHz Frequency Recommended Recommended Hold Nominal 50% 50% Duty Cycle Specification Valve C Valve D (EPDM Seal) Hit Voltage Level Rated Voltage Rated Voltage Minimum Hit Time 50 ms 25 ms Maximum Hit Time N/A 50 ms Hold (PWM) 5 kHz Min., 15 kHz 1 kHz Min., 20 kHz Frequency Recommended Recommended Hold Nominal 50% 50-60% Duty Cycle
Control scheme of pump regulation: PV(f)--flow process variable, ml/s; SP(f)--set point flow, ml/s; MV (PWM code)--manipulated variable, 0...
For switched boost inverter, a modified unipolar sine PWM switching technique is used [9].
In accordance with this purpose, a PWM driver control system [33,34], which can adjust the current value of model filter solenoid system within three regions with time, is designed and the effects of this system on the filter performance is investigated.
Nevertheless, this paper analyzes the PWM rectifier with a different approach.
With the development of power electronics and control theory, in order to improve the control performance and reduce system cost and harmonics, numerous modern control strategies have been studied and applied in an attempt to the control system of three-phase PWM rectifier [9-15].
Measurements related to impact of the PWM control frequency onto efficiency of Permanent Magnet Synchronous Motors (PMSM) were carried out within the first zone of the motor control due to operation of the motor with the load torques up to 6 Nm.