This power-supply circuit illustrates most of the details that seldom get mentioned in textbooks, but are essential in the real world. The extra component count in this circuit pays handsomely in ensuring a power supply that is robust under field conditions. Although this extra care in design might appear to be a display of unnecessary compulsiveness, in fact it is hard-nosed cost-effectiveness -- each field failure under warranty costs the manufacturer at least a hundred dollars in real shipping and repair costs, not to mention the tarnished reputation produced by persistent failure.