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Field-gradient coils in MRI machines are driven by relatively high-power PWM amplifiers. Historically, a crude form of PWM has been used to play back PCM digital sound on the PC speaker, which is driven by only two voltage levels, typically 0 V and 5 V. By carefully timing the duration of the pulses, and by relying on the speaker's physical ...
It is analogous to pulse-width modulation (PWM), in which the magnitude of an analog signal is encoded in the duty cycle of a square wave. Unlike PWM, in which the width of square pulses is varied at a constant frequency, PFM fixes the width of square pulses while varying the frequency.
Vs may be greater than 10 V so that a maximum intended value of Rc produces a 10 V maximum control voltage. Rc must be adjusted to a value of 0 ohms (a direct short) to return a 0 V control voltage. As a practical matter, many 0-10 V dimming control inputs can be operated by replacing the variable control resistor with an electronic switch.
Servo and receiver connections A diagram showing typical PWM timing for a servomotor. Servo control is a method of controlling many types of RC/hobbyist servos by sending the servo a PWM (pulse-width modulation) signal, a series of repeating pulses of variable width where either the width of the pulse (most common modern hobby servos) or the duty cycle of a pulse train (less common today ...
This unit is wired in series with the load. Diodes (D2, D3, D4 and D5) form a bridge, which generates pulsed DC. R1 and C1 form a circuit with a time constant. As the voltage increases from zero (at the start of every halfwave) C1 charges up. When C1 is able to make Zener diode D6 conduct and inject current into the SCR, the SCR fires. When the ...
The following table compares cathode-ray tube (CRT), liquid-crystal display (LCD), plasma and organic light-emitting diode (OLED) display device technologies. These are the most often used technologies for television and computer displays.
If the supply has a DC output, its time base is of no importance in deciding when to pulse the supply on or off, as the value that will be pulsed on and off is continuous. PFC differs from pulse-width modulation (PWM) in that it addresses supplies that output a modulated waveform, such as the sinusoidal AC waveform that the national grid outputs.
AC/DC converters are used every time an electronic device is connected to the mains (computer, television etc.). These may simply change AC to DC or can also change the voltage level as part of their operation. AC/AC converters are used to change either the voltage level or the frequency (international power adapters, light dimmer).