an inverter, another inverting amplifier is required to control it, increasing schematic complexity compared to simple linear regulator. Power FETs may be preferable in order to reduce power consumption, yet this poses problems when the regulator is used for low input voltage, since FETs usually require 5 to 10 V to close completely. Power FETs may also increase the cost. Efficiency and heat dissipation The power dissipated in the pass element and internal circuitry () of a typical LDO is calculated as follows: where is the quiescent current required by the LDO for its internal circuitry. Therefore, one can calculate the efficiency as follows: where However, when the LDO is in full operation (i.e., supplying current to the load) generally: . This allows us to reduce to the following: which further reduces the efficiency equation to: It is important to keep thermal considerations in mind when using a low drop-out linear regulator. Having high current and/or a wide differential between input and output voltage could lead to large power dissipation. Additionally, efficiency will suffer as the differential widens. Depending on the package, excessive power dissipation could damage the LDO or cause it to go into thermal shutdown. Quiescent current Among other important characteristics of a linear regulator is the quiescent current, also known as ground current or supply current, which accounts for the difference, although small, between the input and output currents of the LDO, that is: Quiescent current is current drawn by the LDO in order to control its internal circuitry for proper operation. The series pass element, topologies, and ambient temperature are the primary contributors to quiescent current. Many applications don't require an LDO to be in full operation all of the time (i.e. supplying current to the load). In this idle state the LDO still draws a small amount of quiescent current in order to keep the internal circuitry ready in case a load is presented. When no current is being supplied to the load, can be found as follows: Filtering In addition to regulating voltage, LDOs can also be used as filters. This is especially useful when a system is using switchers, which introduce a ripple in the output voltage occurring at the switching frequency. Left alone, this ripple has the potential to adversely affect the performance of oscillators, data converters, and RF systems being powered by the switcher. However, any power source, not just switchers,