Week 18

Progress:

4.1.2 Working Topology

            LEDs use solid state semiconductor technology similar to those used in modern microprocessors. The parts of an LED are two semiconductor materials layered on substrate and powered by a low direct-current voltage; electrons released from the negative n-type layer combine with holes from the positive p-type. When electron-hole pairs are combined, a photon of light is emitted from the active layer. The semiconductor is often called a chip. The chips can be packaged in a variety of optical refracting forms to enhance the light output. The most common type has been the bullet-shape (T-1) that encases the chip in a 5mm epoxy package. Current advances in chip packaging configurations now allow for improved directional control of the light output, better thermal management and overall flexibility in design of light fixtures.

Incandescent lamp creates light by heating a thin filament to a high temperature above 2500 °C and then turns the heat to the visible light. Hence, over 90% for the energy is transfer to the invisible infrared light or heat.

To let the fluorescent lamp and the halogen lamp glow up, the energy is used to produce ultraviolet light and then the electricity is passed across the tube through the mercury vapor to make the phosphor coating glow or fluorescent. Hence, the efficiency for the fluorescent lamp will be decreased during the process of the generation of the ultraviolet light and converting the ultraviolet light to the visible light.

                The working topology for LEDs is much simpler. The simplest topology is by using a current limit resistor to control the current passing through the LEDs. Developing the DC-DC converter with current regulation can make the power circuit more reliable.