Unit –III�Voltage Regulators

-10 Marks

Course Outcome

Maintain IC Voltage regulator and SMPS

Introduction

^•Power supply: a group of circuits that convert the standard ac voltage (120 V, 60 Hz) provided by the wall outlet to constant dc voltage

^•Transformer : a device that step up or step down the ac voltage provided by the wall outlet to a desired amplitude through the action of a magnetic field

Introduction

• Rectifier: a diode circuits that converts the ac input voltage to a pulsating dc voltage
• The pulsating dc voltage is only suitable to be used as a battery charger, but not good enough to be used as a dc power supply in a radio, stereo system, computer and so on.

Introduction

• There are two basic types of rectifier circuits:
• Half-wave rectifier
• Full-wave rectifier - Center-tapped & Bridge full-wave rectifier
• In summary, a full-wave rectified signal has less ripple than a half-wave rectified signal and is thus better to apply to a filter.

Introduction

• Filter: a circuit used to reduce the fluctuation in the rectified output voltage or ripple. This provides a steadier dc voltage.
• Regulator: a circuit used to produces a constant dc output voltage by reducing the ripple to negligible amount. One part of power supply.

Voltage Regulation

^•Two basic categories of voltage regulation are:

• line regulation
• load regulation

​

^•The purpose of line regulation is to maintain a nearly constant output voltage when the input voltage varies.

^•The purpose of load regulation is to maintain a nearly constant output voltage when the load varies

Line Regulation

Line regulation: A change in input (line) voltage does not significantly affect the output voltage of a regulator (within certain limits)

Line Regulation

^•Line regulation can be defined as the percentage change in the output voltage for a given change in the input voltage.

Δ means “a change in”

^•Line regulation can be calculated using the following formula:

^⎟ ×100%

⎝ ^IN ⎠

^{⎛ ΔV}OUT ^⎞

Line regulation = ^⎜ _ΔV

ΔV_IN

Line regulation = ^{(ΔVOUT /VOUT )×100%}

Load Regulation

Load regulation: A change in load current (due to a varying R_L) has practically no

effect on the output voltage of a regulator (within certain limits)

Load Regulation

^•Load regulation can be defined as the percentage change in the output voltage from no-load (NL) to full-load (FL).

^VNL

= the no-load output voltage

V_FL = the full-load output voltage

^⎟ ×100%

FL ⎠

V

−V_FL ^⎞

^{⎛ V}NL

Load regulation = ^⎜

⎝

^•Where:

IC Voltage Regulators

^•Regulation circuits in integrated circuit form are widely used.

^•Their operation is no different but they are treated as a single device with associated components.

^•These are generally three terminal devices that provide a positive or negative output.

^•Some types have variable voltage outputs.

^•A typical 7800 series voltage regulator is used for positive voltages.

^•The 7900 series are negative voltage regulators.

^•These voltage regulators when used with heatsinks can safely produce current values of 1A and greater.

^•The capacitors act as line filtration.

IC Voltage Regulators

^•Several types of both linear (series and shunt) and switching regulators are available in integrated circuit (IC) form.

^•Single IC regulators contain the circuitry for:

1. reference source
2. comparator amplifier
3. control device
4. overload protection

^•Generally, the linear regulators are three-terminal devices that provides either positive or negative output voltages that can be either fixed or adjustable.

Fixed Voltage Regulator

^•The fixed voltage regulator has an unregulated dc input voltage V_i applied to one input terminal, a regulated output

dc voltage V_o from a second terminal, and the third terminal connected to ground.

Fixed-Positive Voltage Regulator

^•The series 78XX regulators are the three-terminal devices that provide a fixed positive output voltage.

Fixed Voltage Regulator

^•An unregulated input voltage V_i is filtered by a

capacitor C₁ and connected to the IC’s IN terminal.

^•The IC’s OUT terminal provides a regulated +12 V, which is filtered by capacitor C₂.

^•The third IC terminal is connected to ground (GND)

Fixed Voltage Regulator

Positive-Voltage Regulators in the 78XX Series

Fixed Voltage Regulator

Fixed-Negative Voltage Regulator

^•The series 79XX regulators are the three-terminal IC regulators that provide a fixed negative output voltage.

^•This series has the same features and characteristics as the series 78XX regulators except the pin numbers are different.

Fixed Voltage Regulator

Negative-Voltage Regulators in the 79XX Series

Fixed Voltage Regulator

Fixed-Negative Voltage Regulator

^•The series 79XX regulators are the three-terminal IC regulators that provide a fixed negative output voltage.

^•This series has the same features and characteristics as the series 78XX regulators except the pin numbers are different.

Fixed Voltage Regulator

Negative-Voltage Regulators in the 79XX Series

Fixed Voltage Regulator

Adjustable-Voltage Regulator

^•Voltage regulators are also available in circuit configurations that allow to set the output voltage to a desired regulated value.

^•The LM317 is an example of an adjustable-voltage regulator, can be operated over the range of voltage from

1.2 to 37 V.

Summary

^•Voltage regulators keep a constant dc output despite input voltage or load changes.

^•The two basic categories of voltage regulators are linear and switching.

^•The two types of linear voltage regulators are series and shunt.

^•The three types of switching are step-up, step- down, and inverting.

Summary

^•Switching regulators are more efficient than linear making them ideal for low voltage high current applications.

^•IC regulators are available with fixed positive or negative output voltages or variable negative or positive output voltages.

^•Both linear and switching type regulators are available in IC form.

^•Current capacity of a voltage regulator can be increased with an external pass transistor.

Switched Mode Power Supply