Introduction to Linear Voltage Regulators Krishna Kishore Reddy K 2010H223084H

Power Supply System for a Laptop

CMOS linear regulators can be categorized as low supply current, large current, high voltage, high-speed, LDO, and so on. The first considerations for choosing a linear regulator are input voltage (VI), output voltage (VO), and output current (IO). PI = PO + PD

Types of voltage regulators Switching regulators: A switching regulator takes in a DC voltage, converts it into a high- frequency voltage, then filters this AC voltage to convert it back into a DC voltage at the output. Linear regulators: Linear regulators use a transistor operated in its linear region as a variable resistor in a voltage divider network to obtain the desired output voltage. Linear regulators are less efficient than switching regulators because the transistor at the output, usually a PMOS, is always dissipating power in the form of heat. Output voltage ripple and noise is lower than in switching regulators. Cascaded regulators: Switching and Linear regulators architectures are cascaded. LDO regulators: Low DropOut (LDO) regulator, named for the small difference between its required supply voltage and the desired output voltage. Feedback is used to modulate the gate voltage and control output impedance

CMOS linear regulators are widely used in battery-powered portable electronics devices because of their low dropout and low supply current characteristics. Some Specifications: Dropout voltage is defined as the difference between the unregulated supply voltage and regulated output voltage. Decreasing the area of a voltage regulator also improves portability. The higher the bandwidth of a regulator, the more quickly it can react to changes in input and power supply and keep the output voltage constant.

Performance Regulated Output Voltage (V olt ) : The output regulated voltage (V olt ) represents minimum and maximum amounts in continuous mode (DC). Output Current (I OUT ) The output current (I OUT ) is measured under specified conditions. Dropout Voltage (V D ) The dropout voltage is the minimum voltage drop across the regulator to maintain output voltage regulation The LDO type requires the least voltage across it, while the standard type requires the most. Quiescent Current (I Q ) Quiescent current (I Q ) is measured in amperes (A) during the idling state. Quiescent current is also called operating current or ground current. Quiescent current never makes it to the load, but flows from the battery to power the regulator itself. Operating Temperature: This is the ambient temperature range through which the device is designed to operate. Ripple Rejection Rate =20*Log (change in output voltage / change in input voltage)

The power from a voltage converter changes dramatically for different applications. A buck converter produces the low DC voltage required by a microprocessor. A boost converter increases the battery voltage to the level required by the disk drive. A DC-to-AC converter produces the high frequency AC voltage that supplies the display. The energy efficiency of a DC–DC converter is The power consumed by the parasitic impedances of the components within a voltage converter is

Vo = VREF × (R1 + R2) / R2

Schematic Diagram of a LDO

References _Chips/IC_Voltage_Regulators Digital Designer’s Guide to Linear Voltage Regulators and Thermal Management – Texas Instruments ELE 3520 Electronic Hardware Computer Analysis and Description