Introduction to Linear Voltage Regulators

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Introduction to Linear Voltage Regulators
Krishna Kishore Reddy K 2010H223084H
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Power Supply System for a Laptop
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The first considerations for choosing a linear
regulator are input voltage (VI), output voltage
(VO), and output current (IO).
PI PO PD
CMOS linear regulators can be categorized as low
supply current, large current, high voltage,
high-speed, LDO, and so on.
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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
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CMOS linear regulators are widely used in
battery-powered portable electronics devices
because of their low dropout and low supply
current characteristics. Some Specifications Dr
opout 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.
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Performance Regulated Output Voltage (Volt)  
     The output regulated voltage (Volt)
represents minimum and maximum amounts
in continuous mode (DC). Output Current (IOUT) 
     The output current (IOUT) is measured under
specified conditions. Dropout Voltage (VD)      
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 (IQ)      
Quiescent current (IQ) 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
20Log (change in output voltage /
change in input voltage)
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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 DCDC
converter is
The power consumed by the parasitic impedances of
the components within a voltage converter is
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Vo VREF (R1 R2) / R2
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Schematic Diagram of a LDO
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References http//www.globalspec.com/Specificati
ons/Semiconductors/Power_Management_Chips/IC_Volta
ge_Regulators Digital Designers Guide to Linear
Voltage Regulators and Thermal Management Texas
Instruments ELE 3520 Electronic Hardware
Computer Analysis and Description