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Switched Mode Power Supply
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 Converter2. Push-pull Converter3. Half bridge Converter4. Full bridge Converter
• Applications of SMPS• Conclusion
• Conclusion
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
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.
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
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.
• 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.
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
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 Cost
Energy Storage
Voltage Relation
Features
Buck 0-1000 1.0 Single inductor
0 ≤ Out ≤ InV2=D.V1
Continuous current at output
Boost 0-150 1.0 Single inductor
Out ≥ InV2=V1.[(1)/(1-D)]
Continuous current at input
Buck-boost
0-150 1.0 Single inductor
Out ≤ 0V2= -V1[(D)/(1-D)]
No continuous current
Use of various transformer isolated topologies:
Working of various SMPS Topologies:
1. Flyback converter:
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
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
Waveform Summary:
2. Push-Pull Converter:
Operation of the Push-Pull Converter:
• Q1 ON, Vs across the lower primary winding• Q2 ON, Vs across the upper primary winding
3.Half-Bridge Converter:
Mode 1 Operation
• Q1 ON, D1 is conducting• Energy transferred to the load
Mode 2 Operation
• Both transistors are OFF• D1 continues to conduct due to current in L1
Mode 3 Operation:
• Q2 ON, D2 conducting• Energy transferred to the load
Mode 4 Operation
• Both transistors OFF• D2 continues to conduct due to current in L1
Waveform Summary – k<0.5
Full-Bridge Converter:
Mode 1 Operation
• Q1,Q4 ON, Q2,Q3 OFF
• D1 conducting, energy transferred to the load
Mode 2 Operation
• All transistors are OFF• D1 continues to conduct due to current in L1
Mode 3 Operation
• Q2,Q3 are ON, Q1,Q4 OFF
• D2 conducting, energy transferred to the load
Mode 4 Operation
• All transistors are OFF• D2 continues to conduct due to current in L1
Waveform Summary – k<0.5
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
SMPS in Indian markets:
iball 600WRs. 4700
Antec 750WRs. 6600
Cooler master 550WRs. 3800
Corsair 750WRs. 10700
Seasonic 500WRs. 3600
UMAX 450WRs. 570
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.orgwww.howstuffworks.comPhilips semiconductors manualLambda semiconductors manualMotorola semiconductors manualMicrochip manual
Thank you!!
Questions?