2. Regulated D.C. Power Supply
•Contents:
1. Ordinary D.C. Power Supply
2. Important Terms
3. Regulated Power Supply
4. Types of Voltage Regulators
5. Zener Diode Voltage Regulator
6. Conditions for Proper Operation of Zener Regulator
7. Transistor Series Voltage Regulator
8. Series Feedback Voltage Regulator
9. Short-Circuit Protection
10. Fold-back Current Limiting
11. Transistor Shunt Voltage Regulator
12. Shunt Feedback Voltage Regulator
13. I.C. Voltage Regulators (Commercial I.C.’s)
1. Fixed Positive Voltage Regulators
2. Fixed Negative Voltage Regulators
3. Adjustable Voltage Regulators
4. Dual-Tracking Voltage Regulators
4. • Important Terms
• Load Regulation
LR = V nl – V fl
% LR = (V nl – V fl) / V fl ≈ (V nl – V fl) / V nl
• Source Regulation
SR = V hl – V ll
%SR = (V hl – V ll) / V nom
Regulated D.C. Power Supply
5. • Output Impedance
Z out (CL) = Z out / (1 + AB)
• Ripple Rejection (usually referred in dB)
RR = V r(out) / V r(in)
dB RR = 20 log (V r(out) / V r(in) )
Regulated D.C. Power Supply
8. • Limitations
A zener diode regulator has the following drawbacks :
1. It has low efficiency for heavy load currents. It is because if the
load current is large, there will be considerable power loss in the
series limiting resistance.
2. The output voltage slightly changes due to zener impedance as
Vout= Vz+ I zZ z. Changes in load current produce changes in
zener current. Consequently, the output voltage also changes.
Therefore, the use of this circuit is limited to only such applications
where variations in load current and input voltage are small.
Regulated D.C. Power Supply
9. • Types of Voltage Regulators
Regulated D.C. Power Supply
10. • Zener Diode Voltage Regulator (shunt voltage regulator)
Regulated D.C. Power Supply
11. • Conditions for Proper Operation of Zener Regulator
1. The zener must operate in the breakdown region or
regulating region i.e. between IZ (max) and IZ
(min). The current IZ (min) (generally 10 mA)
2. The zener should not be allowed to exceed
maximum dissipation power otherwise it will be
destroyed due to excessive heat.
3. There is a minimum value of RL to ensure that
zener diode will remain in the regulating region i.e.
breakdown region.
Regulated D.C. Power Supply
12. • Transistor Series Voltage Regulator
Vout = VZ − VBE
Regulated D.C. Power Supply
15. • Short-Circuit Protection
Let us consider the example as follows:
Regulated D.C. Power Supply
The input potential is
20 Volts, the output
potential is 10 Volts,
the load is 5 ohms this
would put the load
current 2 Amperes
resulting in the power
dissipated by the main
series Transistor to be
P = Vce x Ic
= (20 – 10) x 2
= 20 Watts
Which means a huge
heat sink
20 V
+
10
-
5Ω
So This valuable transistor
needs Short-Circuit Protection
16. • Short-Circuit Protection
Current Limitting Circuit
Regulated D.C. Power Supply
The Power Disspation in this circuit is about
20 Watts (Too Much Power wasted)
18. •
Regulated D.C. Power Supply
In This Case we may
Make the power less to
about %50 less or even
more
19. • Transistor Shunt Voltage Regulator
Vout = Vz + VBE
A shunt voltage
regulator provides
regulation
by shunting (passing)
current away from the
load to regulate the
output voltage.
Regulated D.C. Power Supply
20. • Drawbacks. A shunt voltage regulator has the following
drawbacks :
1. A large portion of the total current through RS flows
through transistor rather than to the load resulting in a
considerable power loss in RS.
2. There are problems of overvoltage protection in this
circuit.
For these reasons, a series voltage regulator is preferred
over the shunt voltage regulator.
Regulated D.C. Power Supply
22. • IC Voltage Regulators
1. Fixed Positive Voltage Regulators
2. Fixed Negative Voltage Regulators
3. Adjustable Voltage Regulators
4. Dual-Tracking Voltage Regulators
Regulated D.C. Power Supply
27. • IC Voltage Regulators
2. Fixed Negative Voltage Regulators
Regulated D.C. Power Supply
28. • IC Voltage Regulators
3. Adjustable Voltage Regulators
Vout = 1.25 ( ( R2 / R1) + 1)
Regulated D.C. Power Supply
29. Example. In Fig. R2 is adjusted to 2.4 kΩ. Determine the regulated
D.C. output voltage for the circuit.
Solution. The regulated D.C. output voltage for the circuit is
given by ;
Regulated D.C. Power Supply
30. • IC Voltage Regulators
4. Dual-Tracking Voltage Regulators
Regulated D.C. Power Supply
