Experimental PWM Controlled Device

Using Pulse-Width Modulation (PWM) for LEDs powering, the frequency should be high enough so that the human eye does not notice flicker. High frequency also allows for a significant energy efficiency: most LEDs have a peak of the efficiency close to the maximum current allowed. Thus, the pulse switching on the current maximum with brightness adjustment by changing the duty ratio gives a greater efficiency compared to current adjustment. Current modes in this case are below the nominal, which leads to an increase in the service life of the lamp. The driver topology offered by some manufacturers, despite a number of advantages, such as a small number of components, a high power factor and efficiency, has a serious drawback - a large flicker rate at the frequency of 100 Hz (about 30%). This circumstance makes such drivers unsuitable for the use in lighting workplaces where this indicator is limited. It is known that high-frequency pulsations have less effect on the eyes than low-frequency ones, so manufacturers try to shift the pulsations to the high-frequency part of the spectrum, where they will be invisible and harmless. The analytical studies of the inertial properties of vision have shown that a significant factor in the formation of visual sensations is not only the frequency, but also the signal's duty cycle. Therefore, for experimental studies, the authors made a device, that can simultaneously change the frequency and duty cycle. The article presents a block diagram of the device and electrical scheme. The device is tested for the operation in various modes.