Voltage Regulators and PLL

Analog Circuits: Voltage Regulators and PLL

Contents

Describe Voltage Regulation using Series and Shunt Regulators 2

Describe characteristics of Voltage Regulators 3

List and describe various types of Voltage Regulators 4

Describe Three-terminal Voltage Regulator ICs 5

Describe Fixed and Adjustable Voltage Regulator ICs 6

Recall Dual Power Supply 7

Describe the types and block diagram of SMPS 8

Differentiate between Linear Power Supply and SMPS 9

Describe block diagram and working of PLL 11

Describe the PLL IC 565 12

Describe Voltage Regulation using Series and Shunt Regulators

Voltage regulation is the process of maintaining a stable output voltage despite changes in input voltage or load conditions. Series and shunt regulators are two commonly used techniques to achieve voltage regulation in electronic circuits.

  1. Series Regulator:
    • In a series regulator, a series pass element (usually a transistor) is placed in series with the load and the input voltage source.
    • The series pass element acts as a variable resistance, adjusting its resistance to maintain a constant output voltage.
    • A feedback mechanism is employed to compare the output voltage with a reference voltage and control the series pass element accordingly.
    • The series regulator actively regulates the voltage by adjusting the resistance in the series path to compensate for variations in the input voltage or load conditions.
  2. Shunt Regulator:
    • In a shunt regulator, a shunt element (usually a Zener diode or voltage reference) is connected in parallel with the load.
    • The shunt element provides a stable reference voltage, and it conducts excess current to maintain a constant voltage across the load.
    • When the input voltage increases, the shunt element diverts the excess current away from the load, preventing the output voltage from rising too much.
    • Conversely, when the input voltage decreases, the shunt element allows more current to flow through the load, compensating for the voltage drop.
    • The shunt regulator regulates the voltage by providing a path for excess current and maintaining a constant voltage across the load.

Both series and shunt regulators have their advantages and are suitable for different applications. Series regulators are often used when a high current capability is required, while shunt regulators are commonly employed for low power applications or when precise voltage references are needed.

It’s important to note that both series and shunt regulators may include additional components such as resistors, capacitors, and feedback networks to enhance their performance and stability. The specific design and implementation of the regulator depend on the desired voltage regulation requirements and the characteristics of the load and input source.

Describe characteristics of Voltage Regulators

Voltage regulators are electronic devices used to maintain a constant output voltage level from a varying input voltage level. They can be broadly classified into two categories – series and shunt regulators. The main characteristics of voltage regulators are as follows:

  1. Output voltage regulation: The primary function of voltage regulators is to regulate the output voltage to a fixed value regardless of variations in the input voltage or load current. This is achieved by using feedback circuits that monitor the output voltage and adjust the voltage regulation element to maintain a constant output voltage.
  2. Line regulation: This is a measure of the ability of the regulator to maintain a constant output voltage in the presence of variations in the input voltage. It is expressed as the percentage change in output voltage for a given percentage change in input voltage, usually expressed in mV/V or %/V.
  3. Load regulation: This is a measure of the ability of the regulator to maintain a constant output voltage in the presence of variations in the load current. It is expressed as the percentage change in output voltage for a given percentage change in load current, usually expressed in mV/mA or %/mA.
  4. Ripple rejection: This is a measure of the ability of the regulator to reject AC ripple voltage present on the input voltage. It is expressed as the ratio of the AC ripple voltage present on the output voltage to the AC ripple voltage present on the input voltage.
  5. Dropout voltage: This is the minimum voltage difference between the input and output of the regulator required for it to operate within its specified regulation limits.
  6. Quiescent current: This is the current drawn by the regulator when no load is connected to its output. It is also referred to as the standby current or the ground current.
  7. Thermal protection: Voltage regulators may be designed to include thermal protection to prevent damage to the device due to overheating. This is achieved by incorporating temperature sensing circuits that shut down the regulator if the operating temperature exceeds a certain threshold.

Overall, voltage regulators provide stable and reliable power to electronic circuits, which is essential for their proper operation.

List and describe various types of Voltage Regulators

There are several types of voltage regulators, some of which are:

  1. Linear Voltage Regulators: These regulators are widely used and provide a stable output voltage with a relatively low noise level. They work by varying the resistance of a series pass transistor to maintain a constant output voltage.
  2. Switching Voltage Regulators: These regulators work by continuously switching a transistor on and off to regulate the output voltage. They are more efficient than linear regulators but produce more noise.
  3. Zener Diode Voltage Regulators: These regulators use a Zener diode to maintain a constant voltage across the load. They are simple and inexpensive but have a limited current capability.
  4. Integrated Circuit Voltage Regulators: These regulators are designed to be used with integrated circuits and are typically found on the same chip as the IC. They are simple to use and have a low dropout voltage.
  5. Programmable Voltage Regulators: These regulators allow the output voltage to be programmed using external resistors. They are used in applications where the output voltage needs to be adjusted frequently.
  6. High Voltage Regulators: These regulators are used in applications that require high output voltages. They can generate output voltages of up to several hundred volts.
  7. Low Dropout Regulators: These regulators can maintain a stable output voltage even when the input voltage is very close to the output voltage. They are used in applications where a small voltage drop is required.

Describe Three-terminal Voltage Regulator ICs

Three-terminal voltage regulator ICs, also known as linear voltage regulators, are integrated circuits that provide regulated output voltage from a varying input voltage. They are widely used in electronic devices to provide a stable and reliable voltage source for powering other components. The three-terminal voltage regulator ICs typically have three pins: input (VIN), output (VOUT), and ground (GND).

There are mainly two types of three-terminal voltage regulator ICs: positive voltage regulators and negative voltage regulators.

Positive Voltage Regulators:

  • Positive voltage regulators provide a regulated positive output voltage.
  • The most commonly used positive voltage regulator is the 78XX series, where XX represents the output voltage.
  • Examples include 7805 (5V output), 7812 (12V output), and 7809 (9V output).
  • These regulators have a voltage reference, error amplifier, pass transistor, and current limiting circuitry built-in.
  • They require a higher input voltage than the desired output voltage to function properly.
  • They can provide a constant output voltage within their specified voltage range, even with varying input voltage and load conditions.
  • They are available in fixed output voltage versions.

Negative Voltage Regulators:

  • Negative voltage regulators provide a regulated negative output voltage.
  • The most commonly used negative voltage regulator is the 79XX series, where XX represents the output voltage.
  • Examples include 7905 (-5V output), 7912 (-12V output), and 7909 (-9V output).
  • Similar to positive voltage regulators, negative voltage regulators have a voltage reference, error amplifier, pass transistor, and current limiting circuitry.
  • They also require a higher input voltage in magnitude than the desired negative output voltage.
  • They provide a constant output voltage within their specified voltage range, compensating for input voltage and load variations.
  • Negative voltage regulators are also available in fixed output voltage versions.

Three-terminal voltage regulator ICs are popular due to their simplicity of use, compact size, and low cost. They find widespread application in various electronic devices such as power supplies, consumer electronics, industrial equipment, and automotive systems. It is important to choose the appropriate voltage regulator IC based on the required output voltage, current capability, and other specifications to ensure reliable and stable voltage regulation.

Describe Fixed and Adjustable Voltage Regulator ICs

Fixed and adjustable voltage regulator ICs are two types of three-terminal voltage regulators that provide regulated output voltage from a varying input voltage. The main difference between them is the ability to set the output voltage.

Fixed Voltage Regulator ICs:

  • Fixed voltage regulator ICs provide a specific, predetermined output voltage that cannot be adjusted.
  • Examples include the 78XX series (positive voltage regulators) and the 79XX series (negative voltage regulators), where XX represents the fixed output voltage.
  • These regulators have a voltage reference, error amplifier, pass transistor, and current limiting circuitry built-in.
  • They are designed to provide a constant output voltage within their specified voltage range, regardless of changes in input voltage and load conditions.
  • Fixed voltage regulators are widely used in applications where a specific voltage level is required and no adjustment is needed.

Adjustable Voltage Regulator ICs:

  • Adjustable voltage regulator ICs allow for the adjustment of the output voltage within a certain range.
  • The most commonly used adjustable voltage regulator IC is the LM317, which is a positive voltage regulator.
  • These regulators have additional circuitry, such as a voltage divider, that allows the output voltage to be set by external resistors.
  • By selecting appropriate resistor values, the output voltage can be adjusted to the desired level within the specified range.
  • Adjustable voltage regulators provide flexibility in voltage selection and are commonly used when the output voltage needs to be fine-tuned or when multiple voltage levels are required in a single design.

Both fixed and adjustable voltage regulator ICs offer reliable and stable voltage regulation. The choice between them depends on the specific requirements of the application. Fixed voltage regulators are convenient when a specific voltage level is needed without the need for adjustment. Adjustable voltage regulators provide more flexibility and allow for fine-tuning of the output voltage to meet specific requirements.

Recall Dual Power Supply

A dual power supply is a power supply that provides both positive and negative voltage outputs. It is commonly used in electronic circuits that require a reference point (ground) between the positive and negative voltages, such as operational amplifiers, analog-to-digital converters, and other analog circuits. The dual power supply usually consists of a transformer, a rectifier, and a voltage regulator. The transformer converts the AC mains voltage into a lower AC voltage, which is then rectified to produce a DC voltage. The voltage regulator regulates the DC voltage to the desired output level.

For circuits that combine digital control with a high power function, such as an industrial control application, the requirement for two different positive DC voltage outputs is common. First, a regulated and low-noise 5V supply provides power for the digital control elements such as microcontroller chips and digital signal processors. Secondly, the higher voltage output is then used for switching and motor control functions where a lower supply voltage could require excessively high current flow. Such elements may have less stringent noise requirements; indeed, they may generate noise that needs to be isolated from the digital control circuitry.

Another typical dual power supply application is analog signal processing and amplification circuits such as audio equipment. Having positive and negative output voltages of equal magnitude is required for circuits built around operational amplifiers or the processing and conversion of analog signals using analog to digital converters where waveform characteristics need to be preserved. Often, circuits with very low power requirements can use a single power supply linked to a resistive divider circuit that creates a virtual ground. This simple, low-cost solution is effective as long as the power loss and voltage drop across the resistors are acceptable. For higher power or better efficiency, the dual power supply circuit is necessary.

Describe the types and block diagram of SMPS

Switched-mode power supplies (SMPS) are electronic devices that convert electrical power from one form to another, with high efficiency, through the use of electronic switches, capacitors, and inductors. The basic block diagram of an SMPS includes the following stages:

  1. Rectification: The first stage is the conversion of AC voltage to DC voltage using a rectifier circuit.
  2. Input filter: The rectified voltage is then passed through an input filter, which consists of a capacitor and an inductor. The input filter removes any high-frequency noise that may be present on the input voltage.
  3. Power Factor Correction (PFC): Some SMPS also include a PFC stage, which ensures that the power factor of the input voltage is close to unity. This helps to reduce the harmonic distortion of the input current.
  4. DC-DC Converter: The DC voltage from the input filter is then passed through a DC-DC converter, which can be either a buck converter, boost converter, or buck-boost converter, depending on the required output voltage. The DC-DC converter uses a switching transistor to chop the DC voltage into a high-frequency AC voltage, which is then passed through an output filter.
  5. Output filter: The output filter consists of an inductor and a capacitor, which filter out any high-frequency noise that may be present on the output voltage.
  6. Voltage regulation: The final stage of the SMPS is voltage regulation, which ensures that the output voltage remains constant under varying load conditions.

There are two main types of SMPS: AC-DC and DC-DC. AC-DC SMPS are used to convert the AC voltage from the mains supply to a DC voltage that can be used by electronic devices, while DC-DC SMPS are used to convert one DC voltage to another DC voltage, usually at a different voltage level.

Differentiate between Linear Power Supply and SMPS

Linear power supplies and SMPS (Switched-mode power supplies) are two types of power supply systems that convert AC voltage to a stable
DC voltage.
Linear Power Supply:
The Linear Power Supply is a power supplying circuit which is used in electrical and electronic circuit to supply the DC power to the circuit. It consists of a step-down transformer, rectifier, a filter circuit and voltage regulator.

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Drawback of Linear Power Supply

The drawback of the linear power supply is that the use of a voltage regulator requires a sink which increases the size of the power supply. The voltage regulator dissipates power due to which ohmic losses occur, this increases the temperature, and thus a heat sink is required.

As a consequence of using heatsink and transformer of large size the size of the linear power supply becomes more and this makes the power supply bulky to use. Moreover, dissipation caused by variable resistors decreases the efficiency of linear power supply to 25-50%.


Switched Mode Power Supply

The Switched Mode Power Supply operated on the principle of switching using a MOSFET transistor. It consists of a rectifier circuit, a filter circuit, chopper, chopper controller, output transformer and a filter circuit.

The main differences between them are:

  1. Efficiency: Linear power supplies are less efficient than SMPS, as they use a transformer to step down the AC voltage and then regulate it to produce the desired output voltage. This results in significant power loss due to heat dissipation. SMPS, on the other hand, use high-frequency switching techniques to convert the voltage, resulting in less power loss and higher efficiency.
  2. Size and Weight: Linear power supplies are generally larger and heavier than SMPS due to the transformer and other components required for voltage regulation. SMPS are more compact and lightweight due to the higher frequency switching components used.
  3. Noise: Linear power supplies produce less noise than SMPS due to the lack of high-frequency switching components. SMPS generate more electromagnetic interference and noise, which can affect nearby electronic devices.
  4. Cost: Linear power supplies are generally cheaper than SMPS due to their simpler design and lower production costs. However, for high-power applications, SMPS may be more cost-effective due to their higher efficiency and smaller size.
    In summary, while linear power supplies are simple, reliable, and low cost, they are less efficient and larger than SMPS. SMPS are more complex, but offer higher efficiency, smaller size, and lower electromagnetic interference.

Describe block diagram and working of PLL

PLL, short for Phase-Locked Loop, is a feedback control system that generates an output signal that is in phase and frequency synchronization with an input signal. PLLs are widely used in electronic systems for frequency synthesis, clock synchronization, and demodulation of signals.

The block diagram of a PLL typically consists of four main components: a phase detector (PD), a loop filter (LF), a voltage-controlled oscillator (VCO), and a feedback divider (FD). The input signal is fed to the phase detector, which compares the phase of the input signal with the phase of the output signal of the feedback divider. The output of the phase detector is a voltage proportional to the phase difference between the two signals.

The output of the phase detector is then filtered by the loop filter, which removes unwanted noise and adjusts the loop bandwidth. The filtered output of the loop filter is then applied to the control input of the VCO, which generates an output signal whose frequency is proportional to the input voltage.

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The output of the VCO is also fed to the feedback divider, which divides the frequency of the output signal by a fixed integer factor and provides the divided signal to the input of the phase detector. This completes the feedback loop.

The feedback loop adjusts the phase and frequency of the VCO output signal until it matches the input signal. The phase detector compares the phase of the input signal with the phase of the feedback signal, and the loop filter adjusts the control voltage applied to the VCO to minimize the phase difference between the two signals. The VCO output frequency is adjusted until the phase difference becomes zero, which ensures that the output signal is in phase and frequency synchronization with the input signal.

In summary, a PLL is a feedback control system that locks the frequency and phase of an output signal to an input signal by continuously adjusting the control voltage applied to the VCO through the phase detector and loop filter.

Describe the PLL IC 565

The PLL IC 565 is a monolithic phase-locked loop IC which consists of a voltage-controlled oscillator (VCO), a phase detector, and a variable frequency divider. It is commonly used in applications such as FM demodulation, frequency synthesis, and clock recovery.

The VCO generates a sinusoidal waveform whose frequency is controlled by an external input voltage. The phase detector compares the phase of this output signal with that of a reference signal, and generates an error signal which is proportional to the phase difference between the two signals. This error signal is then used to adjust the frequency of the VCO so as to reduce the phase difference.

The frequency divider, also known as the feedback divider, divides the frequency of the VCO output and feeds it back to the phase detector as the reference signal. The output of the frequency divider is also available as an output of the IC. The frequency division ratio of the feedback divider can be set externally using a set of control pins.

The PLL IC 565 is available in various packages such as DIP, SOIC, and TSSOP. It requires a single power supply voltage and can operate over a wide range of frequencies.

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