Linear and Switching Voltage Regulators: Principles, Advantages, and Disadvantages, Slides of Microelectronic Circuits

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Microelectronics

Unit-3: a)Voltage Regulator

b) Frequency and Compensation Techniques

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 Drop Out (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 Types of voltage regulators

• (^) 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 (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)*

Generalized Circuit for Linear Voltage Regulator

Advantages Of Linear Regulator

• The ripple contents in the output voltage waveforms is very low.
• No RFI/EMI, as the power device is not operated as switch.
• High speed transistor need to be used. Disadvantages Of Linear Regulator
• The efficiency of linear regulators is very low of the order of 40% to 50%. This is due to the operation of series pass power device in the active region.
• Large heat sink for the power transistor is required bulkly.
• A large bulkly 50Hz transformer is required.

Switching Voltage Regulator/Swit

ch Mode Power

Supply

• The block diagram shows that the SMPS is also basically a series regulator. Then how is it different from linear power supply?
• In SMPS, the series pass transistor does not operate in its active region. Instead it operates as a switch.
• The basic switch mode power supply consists of four components namely the unregulated dc voltage source Vin, an electronic switch S, a pulse generator and a filter. OPERATION : The pulse generator generates rectangular pulse which are applied to the control terminal of an electronic switch. This switch is turned on and off with the help of these rectangular pulses.
• The switch is an electronic switch which is typically a transistor or MOSFET. It is used in its saturation and cut-off regions and not in active region.

 (^) The designing of a voltage regulator using MOSFET and some components is very simple which is shown above. This circuit uses two push buttons denoted with SW1 & SW2 which are used for controlling the power of o/p voltage. This voltage regulator is also called push- button voltage regulator because by using these two switches, the power can be increased or decreased within the output section.  (^) Turn on the voltage regulator circuit & push any button, we can observe the main difference within the output. The load used in the output of this circuit is a 12V DC light. Once you press the SW1 switch this circuit will generate more current throughout the IRF MOSFET to make the light ON. Similarly, when you press the SW2 switch, it will decrease the flow of current throughout the MOSFET to make the light OFF.