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?