Patent ID: 8203287

Claim:
A pulse-width modulation (PWM) control device comprising a load; a rectifier being connected to a power module and rectifying a truncated sinusoidal voltage from the power module to a pulsating truncated direct current (DC) voltage; a PWM control module being connected to the power module, generating a PWM control signal and comprising a boost circuit being connected to the rectifier, receiving and boosting the pulsating truncated DC voltage to high DC voltage; a comparator being connected to the power module, sensing zero crossings of the truncated sinusoidal voltage in order to indicate both the duty cycle and frequency of the truncated sinusoidal voltage; a phase-locked loop (PLL) circuit is connected to the comparator, receiving a signal that is indicative of the frequency and phase of the truncated sinusoidal voltage, generating a control signal with fixed frequency and a phase synchronized to the phase of the truncated sinusoidal voltage; a duty cycle detector being connected to the power module and the PLL circuit, determining a duty factor of the truncated sinusoidal voltage emanating from the power module and generating a PWM control signal that converts the control signal from the PLL circuit to the same duty factor as that of the truncated sinusoidal voltage; and a PWM controllable ballast being driven by the boost circuit, being controlled by the PWM control signal and being used for limiting current to a proper value for the load.