2. INTRODUCTION
Linear Power Supplies
Switch Mode Power Supply(SMPS)
Complete Switched Mode Regulator
Step Down Or Buck Switching
Regulator
Switching Boost Regulator
(Step Up Converter)
Switching Buck – Boost Regulator
Cuk Regulators
Comparison Of Switching Regulator
Advantage & Disadvantage Of SMPS
3. Linear Power Supplies
• The series pass transistor is the controlling element
which appears in series with thee load. The voltage
across this transistor is automatically adjust to obtain
the regulated output voltage.
• In the linear regulator the series pass transistor is
operated in its active region.
4. • Therefore the voltage across Vce in the on state is high.
As it is carrying the load current, the power dissipation in
the power transistor is very high.
• The output voltage of the linear regulator is adjusted
automatically at the desired level by adjusting the
voltage across the series pass transistor. This voltage is
adjusted by feeding back a part of the output voltage.
• Due to high power dissipation taking place in the series
pass transistor, the efficiency of linear regulator is low.
• The linear regulators are used in those applications
where we need a very low ripple in the output voltage
and where the voltage regulation should be vary low.
The typical application are computers, video games,
printers etc.
5. Advantages Of Linear Regulator
• The ripple contents in the output voltage waveforms is
very low.
• No RFI/EMI, as the power device is not operated as
switch.
• High speed transistor need to be used.
6. Disadvantages Of Linear Regulator
• The efficiency of linear regulators is very low of the
order of 40% to 50%. This is due to the operation of
series pass power device in the active region.
• Large heat sink for the power transistor is required
bulkly.
• A large bulkly 50Hz transformer is required.
7. Switch Mode Power Supply
• The block diagram shows that the SMPS is also
basically a series regulator. Then how is it different
from linear power supply?
• In SMPS, the series pass transistor does not operate
in its active region. Instead it operates as a switch.
• The basic switch mode power supply consists of four
components namely the unregulated dc voltage
source Vin, an electronic switch S, a pulse generator
and a filter.
8.
9. • The pulse generator generates rectangular pulse
which are applied to the control terminal of an
electronic switch. This switch is turned on and off with
the help of these rectangular pulses.
• The switch is an electronic switch which is typically a
transistor or MOSFET. It is used in its saturation and
cut-off regions and not in active region.
• When the switch is on, it connects the unregulated dc
input Vin as it is to the input of the filter and the filter
input is disconnected from the dc input voltage Vin
when the switch is open circuited.
operation
10. • Filter input voltage = Vin …when switch is on.
• Filter input voltage = 0 …when switch is off.
11. • Therefore at the input of the filter we get a rectangular
waveform. The average value of this waveform can be
adjusted by changing either the duty cycle or
frequency of the rectangular pluses produced by the
pulse generator. The duty cycle is defined as,
• Where , ton = On-time of the pulse wavefoam
toff = Off-time of the pulse wavefoam
12. • Typically, the operating frequency of the switching
regulator will be in the range of 10 to 50 KHz. That
means the total time T is of the order of 100 µS to 20
µS.
• The filter then converts the rectangular waveform at its
input into a smooth dc voltage by removing the ripple
contents.
Or
14. • The series pass transistor Q acts as a switch
• The resistor R1 and R1 from a resistive feedback
network. The feedback voltage is given by:
• This feed back voltage is applied at the non – inverting
(+) termiinal of the error amplifier.
• The difference between feedback voltage and the
reference voltage is called as “error”.
• The dc control voltage is compared with the triangular
waveform generated by the triangular wave generator.
Operation
15. • The comparator output is a rectangular waveform.
This waveform is used to turn on and off transistor.
• The rectangular wave foam at the emitter of Q is
filtered by by the LC filter to produce a pure ripple
free dc voltage at the regular output.
• The size of LC components is small.
16. • If the output V0 reduces below the regulated value,
then the feedback voltage decreases. The output
voltage of error amplifier will decrease.
• This will increase the on time of the pulse at the output
of the comparator. Thus on time ton increase to
increase the duty cycle and hence output voltage will
increase. Thus regulation will be practically achieved.
17. Classification Of SMPS
SMPS
Non isolated
converters
Isolated
converters
Buck
regulator
Boost
regulator Buck boost
regulator
Fly back
converters
Forward
converter
Full bridge
converter
Half bridge
converter
18. • Q1 is a power transistor which is turned ON and OFF
by the rectangular pulses applied at its base.
• DFW is a freewheeling diode, while L and C2 form a
low pass filter. Vin is the unregulated power supply.
Step Down Or Buck Switching
Regulator
19. • As discussed earlier, we can vary the average output
voltage by changing either the duty cycle or
frequency.
• The expression for average output voltage is terms
of duty cycle is given by:
Vo = D x Vin
• The duty cycle “D” can be varied between 0 and 1.
Therefore average output voltage V0 will vary
between 0 and Vin.
• Average output voltage Vo is less then or equal to Vin
this circuit is called as the “switching buck regulator”.
20. • When Q1 is on the input dc voltage V gets connected
at the input of the LC filter.
• Energy is given to the LC filter and the load during
this mode of operation. The diode DFW is reversed
biased remains off.
• When Q1 is turned off, there is a self induced voltage
which appears across the inductance L.
• The output voltage can be varied by varying the duty
cycle of the power transistor. The output voltage is
V out = DV where D =
Waveforms And Operation
Mode 1(when Q1 is on)
Mode 2(when Q1 is off)
21.
22. • It needs only one transistor.
• It is a simple circuit.
• The circuit efficiency is high.
• The di/dt of the load current is limited by inductor L.
• Input current is discontinuous and smoothing input
filter is generally required.
• It can procedure an output voltage of only polarity.
Polarity reversa is not possible.
• The output current is unidirectional.
• It needs a separate protection circuit against a
possible short circuit, across the diode path.
Advantages Of Buck Regulators
Disadvantages
23. • The switching boost regulator also called as step up
converter.
Switching Boost Regulator
24. • When Q1 is on the points X and Y are circuited.
So QXY = 0.
• The voltage across indicator is Vin Volts and the
current through it increases linearly.
• The inductor L stores energy during mode 1.
Waveforms And Operation
Mode 1(when Q1 is on)
25. • As soon as Q1 is turned off, the current through L is
suddenly interrupted.
• This will induce a negative voltage across it to
forward bias diode D.
• The stored energy by the L in mode I is delivered to
the load during this mode.
• It possible to obtain an output voltage which is higher
than the supply voltage, therefore it is known as
boost regulator.
Mode 2(when Q1 is off)
26. • The output voltage can be varied by varying the duty
cycle of the output waveform.
• Where D is the duty cycle. This equation shows that
the output voltage is higher then the input voltage for
all the values of D.
• The boost regulator is used in those applications
where output voltage greater than the input voltage
is required.
27.
28. • It can step up the output voltage without a transformer.
• Its efficiency is high due to the use of single transistor.
• The input current is continuous.
• A high peak current flows through the power transistor.
• Output voltage is sensitive to changes in duty cycle D.
So it is difficult to stabilize the regulator.
• A larger filter capacitor and a large inductor is required
to be used.
Advantages Of Boost Regulators
Disadvantages
29. • The buck-boost regulator is a non isolated type
converter and it is also known as inverting regulator.
• The buck-boost regulator is a type of flyback
converter whose operation is very similar to a boost
regulator.
Switching Buck Boost Regulator
30. • When Q1 is turned on, the supply voltage V gets
conneted across the inductance L. The inductance
current starts increasing linearly. Diode is reversed
biased, the inductance will store energy during this
mode of operation.
• As soon as the transistor Q1 is turned off, the current
through L is interrupted abruptly.
• A negative voltage is induced into L which will forward
bias diode D1.
• This mode comes to an end when the current through
diode reduces to zero.
Waveforms And Operation
Mode 1(Q1 is on)
Mode 2(Q1 is off D1 is on)
31. • When all the devices are in the off state, the capacitor
C2 will discharge through the load in this mode of
operation. This circuit is called as inverting as the
output voltage is negative.
• This regulator is used in those applications where
output voltage grater rhen the input voltage with a
negative polarity.
• The waveforms are for the discontinuous condition.
The conduction can be made continuous by increasing
the duty cycle above 50%.
• But with a duty cycle value above 50% the stability
and regulation problem will have to be faced.
• The buck boost regulator has all drawbacks of the
boost regulator.
Mode 3(All devices off)
32.
33. • This circuit produces a negative output voltage without
transformer.
• Its efficiency is high.
• The rate of change of fault current (di/dt) is limited to a
safe value by the inductor L.
• Its very easy to implement the short circuited protection.
• Input current is discontinuous.
• A high peak current flows through the transistor
Advantages Of Boost Regulators
Disadvantages
34. • This circuit is similar to the buck-boost regulator but
it provides an output voltage which is less than or
grater than the input voltage with a polarity reversal.
Cuk Regulator
35. • Initially when the input voltage Vs is applied and the
transistor T is in the off state, the capacitor C1
charges through L1 and DM to a voltage equal to Vs .
• The circuit operation can be divided into two modes.
Waveforms And Operation
36. • At t = 0, transistor T is turned ON and it starts acting
as a closed switch. So current through L1 starts
increasing.
• The voltage across C1 gets applied across Dm to
reverse bias it, and turns it off.
• The inductor L1 continues to store energy. Capacitor
C1 will discharge its energy through the circuit formed
by C1, C2, load and L2.
• Mode 1 comes to end at t = t1.
Mode 1 (o to t1)
37. • At t = t1 the transistor T is turned off. Capacitor C1 is
charged from the input supply and the energy stored
in L2 is transferred to the load.
• The diode Dm and transistor T provide a synchronous
switching action.
• C1 act as a medium to transfer energy from source
to load.
Mode 2 (t1 to t2)
38.
39. • The cuk regulator operation is based on the transfer
of capacitor energy. Hence the input current is
continuous.
• This circuit has low switching losses.
• It has a high efficiency.
• A high value peak current flows through the
transistor.
• Ripple current of the capacitor C1 is high.
• This circuit requires an additional capacitor and an
inductor.
Advantages Of Cuk Regulators
Disadvantages
40. Sr.
No
Parameter
Buck
Regulator
Boost
Regulator
Buck Boost
Regulator
1
Average
Output Voltage
Less then or
equal to input
voltage
Equal to or
grater than input
voltage
Less than equal to
or grater than
input voltage
2
Position Of
Transistor
In series with
the load
In parallel with
the load
In series with the
load
3
Number Of
Transistor
One One One
4
Expression for
Output Voltage
V0 = D x Vin
V0 = Vin
(1 – D)
V0 = D X Vin
1 - D
Comparison Of Switching
Regulators
41. • Low power dissipation in the series pass transistor as
it operates as a switch and not in the active region.
• High efficiency due to reduced power dissipation in
the transistor.
• The smaller size of L and C at high operating
frequencies and need of smaller heat sink for the
series pass transistor.
• Higher power handling capacity.
Advantages Of SMPS
42. • Increased switching loss in the series pass transistor
due to high frequency switching.
• Radio Frequency Interference to the neighbouring
electronics circuits.
• There are no isolation between input and output.
• The load requires separate protection circuitry.
• The transient response is slow as compared to the
linear power supplies.
• Ripple content is the output is higher than that for
linear power supply.
• Load regulation is poor as compared to the linear
regulators.
Disadvantages Of SMPS
