IC REGULATORS

1. Voltage Regulators

2. Contents
•Introduction
Series op-amp regulator
IC voltage regulators
723 general purpose regulator
Switching regulator
•
•
•
•

3. Introduction
• The function of voltage regulator is to provide a constant stable dc
voltage for powering other electronic circuits.
• Voltage regulators are classified as:
1.
2.
Series or linear regulator
Switching regulator

4. Series or Linear regulator
•
They use a power transistor connected in series between the
unregulated dc input and load.

5. • The output voltage is controlled by the continuous voltage drop
taking place across the series pass transistor.
As transistors works in the active or linear region, these regulators
also known as linear regulators.
• are
Series or Linear regulator

6. •
•
Series or Linear regulator
Advantages Disadvantages
•Simple circuit configuration
•Few external parts
•Low noise
•Relatively poor efficiency
•Considerable heat generation
•Only step-down (buck)
operation

7. Switching regulators
•• A switching regulator is a voltage regulator that uses a switching element to transform the incoming power
supply into a pulsed voltage, which is then smoothed using capacitors, inductors, and other elements.
•Power is supplied from the input to the output by turning ON a switch (MOSFET) until the desired voltage is
reached.
•Once the output voltage reaches the predetermined value the switch element is turned OFF and no input
power is consumed.
•Repeating this operation at high speeds makes it possible to supply voltage efficiently and with less heat
generation.
• This gives improved efficiency over series regulator.

8. Switching regulators
Advantages Disadvantages
•High efficiency
•Low heat generation
•Boost/buck/negative
voltage operation
possible
•More external parts
required
•Complicated design
•Increased noise

9. Series op-amp regulator
• A voltage regulator is a electronic circuit that provides a stable dc
voltage independent of load, temperature and ac line voltage
variations.

10. • The circuit consists of four major components.
1.
2.
3.
4.
Reference voltage circuit (Zener diode)
Error amplifier (Difference amplifier)
Series pass transistor (Q1)
Feedback network (R1 and R2)

11. • The transistor Q1 is connected as an emitter follower and therefore
provide sufficient current gain to drive the load.
• The output voltage is sampled by potential dividers R1 and R2
(feedback network) and feedback to the inverting input terminal of
the op-amp error amplifier.
• If the output voltage increases say due to variation in load current the
sampled voltage βV0 also increases. Which in turn reduces the output
voltage of the difference amplifier due to the 180⁰ phase shift
provided by the op-amp amplifier.

12. IC Voltage Regulator
There are two categories
1. 78XX / 79XX Fixed Voltage Series regulators
2. 723 general purpose regulators

13. Fixed Voltage Series Regulator
• 78XX series are three terminal positive fixed voltage regulators.
• In 78XX, the last two numbers ‘XX’ indicate the output voltage.
• Eg: 7805
7808
+5V
+8V
• 79XX series are three terminal, negative fixed voltage regulators.

14. • Capacitors are connected between input terminal and ground to cancel the
inductive effect due to long distribution leads. Output capacitance
improves the transient response.

15. Characteristics of IC Voltage Regulators
1.

2.

3.

4.
Regulated output voltage(V0)
78XX has output voltage 5, 6, 8 etc.
Unregulated input voltage(Vin)
i.e If V0=5 V then Vin=7 V|𝑉𝑖| ≥ |𝑉0| + 2𝑉
Maximum output current(I0max)
May vary from 0 to maximum rated current
Thermal shutdown
 Has sensors which turns-off the IC when it becomes
celcious)
too hot (125 to 150 deg

16. Limitations
• No short circuit protection
• Output voltage is fixed

17. Important performance parameters

18. Important performance parameters

19. IC regulator used as current source

20. Current booster circuit

21. Important formulas:

22. Fixed regulator used as adjustable regulator

23. 723 General Purpose Regulator

24. 723 General Purpose Regulator

25. IC 723 PIN Diagram

26. IC 723 as low voltage regulator (Vo= 2V to 7V)

27. IC 723 as high voltage regulator (Vo>7V)

28. Switching Regulator