Power Supplies for LED Driving
Including detailed examples of what works and why, this practical, hands-on book covers the design trade-offs involved in LED driving applications, from low-power to UB-LEDs and beyond.
TABLE OF CONTENTS Power Supplies for LED Driving
Chapter 11: Selecting Components for LED Drivers
This chapter will be very practical in orientation. It will describe how different materials and component types can affect the performance of LED drivers. This will be detailed, showing how the physical construction of components could have an effect.
11.1 Discrete Semiconductors
Atoms of materials have a core (nucleus) of positively charged proton and uncharged neutrons. They have negatively charged electrons orbiting around this nucleus, like planets around the Sun. When atoms combine, they share electrons in their outer orbit (the valence band). Lighter atoms, like silicon, are most stable when there are eight electrons in their outer orbit. Semiconductors are (usually) made from silicon, which has four electrons in its outer orbit.
The addition of a small amount of material (dopant) with either three or five electrons in their atom's outer orbit can create an imbalance because, when combined with the four electrons of silicon, there are either seven or nine electrons in the outer orbit. When doped with material having three electrons in the valence band (boron (B), aluminium (Al), gallium (Ga) or indium (In)), the resultant outer orbit has seven electrons and a hole where an electron is missing. This hole appears as a free positive charge and is called P-type semiconductor. This is shown in Figure 11.1, diagram A.
Figure 11.1: P-Type and N-Type Semiconductors
When doped with material having five electrons in the valence band (phosphorous (P), arsenic (As) or antimony (Sb)), the resultant outer orbit has nine electrons which means that there is a...
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