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I ntroduction We can divide regulators into two major types : Linear regulators Switching mode regulators In this article, we will introduce you to the linear regulators and then we will get to the magical switching supplies! Linear regulators Fig.1 Linear regulator shown in fig.2 produces DC regulated output from a higher DC input supply by simply putting a transistor in series between the input and the output. Fig.2 This series transistor  (called “ series–pass transistor ” or simply “ pass transistor ”) is operated in the linear(ohmic) region of its VI curve. That’s it,  Transistor Q1 acts as a variable resistance that drops the excess voltage across it. So it can be represented as shown in fig.3 . Fig.3 Using simple math, the voltage drop across the resistor is the difference between input and output voltages (this term is called the “headroom”) V = V (in)-V(out) If we want to calculate the dissipated (wasted) p