1. Switched Mode Power Supply

2. Contents:-
• General description of Power Supply
• Advantages/Disadvantages of SMPS
• Block diagram of SMPS
• Basic topologies and practical
• requirements
• Working of various SMPS topologies:
1. Flyback Converter
2. Push-pull Converter
3. Half bridge Converter
4. Full bridge Converter
• Applications of SMPS
• Conclusion

3. Power Supply:-
Any device that supplies electric
power to an electric load.
The different types of power
supplies include:
-Battery
-DC power supply
-AC power supply
-Linear regulated power supply
-Switched mode power supply
-Programmable power supply
-Uninterruptible power supply

4. Switched Mode Power Supply:
 An electrical power supply that incorporates a switching
regulator to convert electrical power efficiently.
 It transfers power from a source, to a load, while
converting voltage and current characteristics.
 Voltage regulation is achieved by varying the ratio of on-
to-off time.

5. Advantages of SMPS over Linear Power Supplies:
• 1. Lower weight
• 2. Smaller size
• 3. Higher efficiency
• 4. Lower power dissipation
• 5. Wide ac input voltage range
• 6. Reduced costs
Disadvantages of SMPS:
1. Complexity of the circuit

6. Block diagram of a SMPS
1. Input rectifier stage:
It is used to convert an ac input to dc. A SMPS with dc
input does not require this stage. The rectifier
produces unregulated dc which is then passed through
the filter circuit.

7. • 2. Inverter stage:
– The inverter stage converts DC, whether directly from the input
or from the rectifier stage described above, to AC by running it
through a power oscillator, whose output transformer is very
small with few windings at a frequency of tens or hundreds
of kilohertz.
3. Output transformer:
- If the output required is to be isolated from input, the inverted
AC is used to draw the primary windings of a high frequency
transformer. This converts the voltage up or down to the
required output level on it’s secondary winding.
4. Output rectifier:
- If the dc output is required, the ac output from the transformer
is rectified.
5. Regulation:
- Feedback circuit monitors the output voltage and compares it
with the reference voltage.

8. Factors to be considered while selecting a
topology for a particular application:-
• 1. Is input-to-output dielectric isolation required for the application?
• 2. Are multiple outputs required?
• 3. Does the prospective topology place a reasonable voltage stress
across the voltage semiconductors?
• 4. Does the prospective topology place a reasonable current stress
across the voltage semiconductors?
• 5. How much of the input voltage is placed across the primary
transformer winding or inductor?
• Typical maximum output power available from each topology:
Converter Topology Maximum output power
Flyback 200W
Forward 300W
Push-pull 500W
Half bridge 1000W
Full bridge >1000W

9. Use of non-isolated topologies:
• Non isolated topologies are the simplest, with the three basic types using a
single inductor for energy storage.
Type Power(W) Relative Energy Voltage Relation Features
Cost Storage
Buck 0-1000 1.0 Single 0 ≤ Out ≤ In Continuous
inductor V2=D.V1 current at
output
Boost 0-150 1.0 Single Out ≥ In Continuous
inductor V2=V1.[(1)/(1-D)] current at
input
Buck- 0-150 1.0 Single Out ≤ 0 No
boost inductor V2= -V1[(D)/(1-D)] continuous
current

10. Use of various transformer isolated topologies:

11. Working of various SMPS Topologies:
1. Flyback converter:

12. Mode 1 Operation -- Q1 ON
• Current builds up in the primary winding
• Secondary winding has the opposite polarity D1 OFF
• C maintains the output voltage, supplies load current

13. Mode 2 Operation -- Q1 turned OFF
• Polarity of the windings reverses
• Diode D1 conducts, charging C and providing current to the load RL
• Secondary current falls to 0 before the next cycle begins

14. Waveform Summary:

15. 2. Push-Pull Converter:

16. Operation of the Push-Pull Converter:
• Q1 ON, Vs across the lower primary winding
• Q2 ON, Vs across the upper primary winding

17. 3.Half-Bridge Converter:

18. Mode 1 Operation
• Q1 ON, D1 is conducting
• Energy transferred to the load

19. Mode 2 Operation
• Both transistors are OFF
• D1 continues to conduct due to current in L1

20. Mode 3 Operation:
• Q2 ON, D2 conducting
• Energy transferred to the load

21. Mode 4 Operation
• Both transistors OFF
• D2 continues to conduct due to current in L1

22. Waveform Summary – k<0.5

23. Full-Bridge Converter:

24. Mode 1 Operation
• Q1,Q4 ON, Q2,Q3 OFF
• D1 conducting, energy transferred to the load

25. Mode 2 Operation
• All transistors are OFF
• D1 continues to conduct due to current in L1

26. Mode 3 Operation
• Q2,Q3 are ON, Q1,Q4 OFF
• D2 conducting, energy transferred to the load

27. Mode 4 Operation
• All transistors are OFF
• D2 continues to conduct due to current in L1

28. Waveform Summary – k<0.5

29. Applications of SMPS:-
• 1. Machine tool industries
• 2. Security Systems
• (Closed circuit cameras)
• 3. Support supplies with PLC’s
• 4. Personal Computers
• 5. Mobile Phone chargers

30. SMPS in Indian markets:
iball 600W Antec 750W Cooler master 550W
Rs. 4700 Rs. 6600 Rs. 3800
Seasonic 500W UMAX 450W
Corsair 750W
Rs. 3600 Rs. 570
Rs. 10700

31. Conclusion:
• The most common SMPS topologies: flyback, push-pull,
half bridge and full bridge converters have been outlined.
• Each has it’s own particular operating characteristics and
advantages, which makes it suitable to particular
applications.
• Some of the most common applications of SMPS have
been discussed.
References:
www.wikipedia.org
www.howstuffworks.com
Philips semiconductors manual
Lambda semiconductors manual
Motorola semiconductors manual
Microchip manual

32. Thank you!!