1. Subject Name: LINEAR INTEGRATED CIRCUITS Subject Code: 10EC46
Prepared By: M.PRIYADHARSINI
Department: ECE
Date: 6/03/2015
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2. UNIT 7
VOLTAGE REGULATORS
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3. TOPIC DETAILS Introduction Voltage Regulation Line Regulation
Load Regulation
Series Regulator
Shunt Regulator
IC Voltage Regulator
Switching Regulator
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4. INTRODUCTION
Batteries are often shown on a schematic diagram as the source of DC voltage but usually the actual DC voltage source is a power supply.
There are many types of power supply. Most are designed to convert high voltage AC mains electricity to a suitable low voltage supply for electronics circuits and other devices.
A more reliable method of obtaining DC power is to transform, rectify, filter and regulate an AC line voltage.
A power supply can by broken down into a series of blocks, each of which performs a particular function.
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5. 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
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6. LINE REGULATION
Line regulation: A change in input (line) voltage does not significantly affect the output voltage of a regulator (within certain limits)
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7. LINE REGULATION
Line regulation can be defined as the percentage change in the output voltage for a
given change in the input voltage.
Line regulation calculated using the formula as
Line regulation = (Δ VOUT/ Δ Vin)*100
Line regulation: A change in input (line) voltage does not significantly affect the output voltage of a regulator (within certain limits)
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8. LOAD REGULATION
Load regulation: A change in load current (due to a varying RL) has practically no effect on the output voltage of a regulator (within certain limits)
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9. LOAD REGULATION
Load regulation can be defined as the percentage change in the output voltage from no-load (NL) to full-load (FL).
Load regulation = (VNL – VFL/ VFL)*100
where:
VNL = the no-load output voltage
VFL = the full-load output voltage
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10. TYPES OF REGULATORS
Fundamental classes of voltage regulators are linear regulators and switching regulators.
Two basic types of linear regulator are the series regulator and the shunt regulator .
The series regulator is connected in series with the load and the shunt regulator is connected in parallel with the load.
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11. SERIES REGULATORS
Control element in series with load between input and output.
Output sample circuit senses a change in output voltage.
Error detector compares sample voltage with reference voltage → causes control element to compensate in order to maintain a constant output voltage.
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12. OP-AMP SERIES REGULATORS
Control Element
Error Detector
Sample Circuit
VREF
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13. OP-AMP SERIES REGULATORS
The resistor R1 and R2 sense a change in the output voltage and provide a feedback voltage.
The error detector compares the feedback voltage with a Zener diode reference voltage.
The resulting difference voltage causes the transistor Q1 controls the conduction to compensate the variation of the output voltage.
The output voltage will be maintained at a constant value of:
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14. IC 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.
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15. IC REGULATORS
The fixed voltage regulator has an unregulated dc input voltage Vi applied to one input terminal, a regulated output dc voltage Vo 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.
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16. FIXED REGULATORS
An unregulated input voltage Vi 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)
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17. FIXED VOLTAGE REGULATORS
Positive-Voltage Regulators in the 78XX Series
IC Part OUTPUT VOLTAGE V V V V V V V V
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18. FIXED VOLTAGE REGULATORS
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.
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19. FIXED VOLTAGE REGULATORS
Negative Voltage regulators in the 79XX Series
IC Part OUTPUT VOLTAGE V V V V V V V V
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20. SWITCHED MODE POWER SUPPLY
Switching regulation is the technique by which an unregulated power is efficiently
converted to regulated load power through the use of controlled switching
devices.
Switching voltage regulators are used where it is required to supply a stable
output voltage from a varying input voltage with a minimum power loss even
under varying load conditions.
A simple switching regulator consists of a control switch (transistor), a low pass
filter and sampling network etc..
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21. SWITCHED MODE POWER SUPPLY
In the circuit S is a transistor used as a control switch. It is switched between
saturation and cut-off.
During ‘ON’ mode the switch is in saturation mode with negligible voltage drop across the collector and emitter terminals of the switch where as in ‘OFF’ mode the switch is in cut-off mode with negligible current through the collector and emitter terminals.
On the contrary the voltage-regulating switch, in a linear regulator circuit, always remains in the active region.
Due to this current is not passed continuously through the transistor and hence the power dissipation is reduced to minimum.
The transistor is switched ON and OFF by an electronic pulse width modulator. The filter circuit smoothens the output wave form and the sampling network (R1-R2) controls the duty cycle such that the output voltage remains constant.
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22. IC VOLTAGE REGULATORS
There are basically two kinds of IC voltage regulators:
Multipin type, e.g. LM723C
3-pin type, e.g. 78/79XX
Multipin regulators are less popular but they provide the greatest flexibility and produce the highest quality voltage regulation
3-pin types make regulator circuit design simple
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23. IC VOLTAGE REGULATORS
The LM723 has an equivalent circuit that contains most of the parts of the op-amp voltage regulator discussed earlier.
It has an internal voltage reference, error amplifier, pass transistor, and current limiter all in one IC package.
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24. IC VOLTAGE REGULATORS-HIGH VOLTAGE CONFIGURATION
Design equations:
Choose R1 + R2 = 10 kW,
and Cc = 100 pF.
External pass transistor and
current sensing added in the circuit
To make Vo variable,replace R1 with a pot.
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25. IC VOLTAGE REGULATORS-LOW VOLTAGE CONFIGURATION
Design equations:
IC 723 With external pass transistor and foldback current limiting
Under foldback condition:
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