Inrush limiter also provides short-circuit protection

摘要

For containing large amounts of bulk capacitance, controlling inrush currents poses problems. The simplest approach involves placing an inrush-limiting resistor in series with the capacitor bank, but a resistor wastes power and adds a voltage drop. The circuit in Figure 1 addresses these problems and provides an additional benefit. At start-up, bipolar PNP transistor Q{sub}2 holds N-channel power MOSFET transistor Q{sub}1 off until the voltage across capacitor C{sub}1 reaches a high enough level to turn off Q{sub}2. During this interval, resistor R{sub}1 supplies C{sub}1 and the rest of the circuit with start-up current. When Q{sub}2 turns off, Q{sub}1 turns on and provides a low-resistance path across R{sub}1. When you shut off external power, the circuit resets as C{sub}1 discharges.