Switch Mode Power supply (SMPS) with Active PFC and PC interface.

1. Introduction:-

Switch mode power supply (SMPS) is a type of an electronic power converter which switches current at a fast rate to increase, decrease, regulate or condition the output voltage or current.

In other words like every other power supply SMPS transfers the power from input to the output like every other power supply but has many advantages in the department of efficiency, cost, size, weight and regulation.

That being said the most important aspect of a switch mode power supply is the high switching frequency. All SMPS operates at a very high switching frequency typically from 25 KHz to 1MHz.

• Isolated.
• Non-isolated

Isolated power supplies have an electrical isolated between input and output In order to achieve that a transformer is used.

Non-isolated power supplies do not have an electrical isolation between input and output. It uses an inductor for voltage conversions.

1. Overview:-

The electric energy is not normally used in the form in which it was produced or distributed. Practically all electronic systems require some form of energy conversion. A device that transfers electric energy from a given source to a given load using electronic circuits is referred to as power supply. Of course, it does not really supply power, it just converts it, so "converter" is a more accurate term for such a device.

A typical application of a DC power supply unit (PSU) is to convert utility AC voltage into a set of regulated DC voltages required for electronic equipment. The energy flow in a modern PSU is controlled with power semiconductors, which can operate in different modes. In original systems they operated in linear mode. Nowadays in most PSUs semiconductors are continuously switching on and off with high frequency. Such units are referred to as switched mode power supplies or SMPS. They offer greater efficiency compared with linear supplies because they can control energy flow with low losses: when a switch is on, it has low voltage drop and will pass any current imposed on it; when it is off, it blocks the flow of current.

As the result, in such a switch the power dissipation which is the product of voltage and current, can be relatively low in both states. Switching mode units are also smaller in size and lighter in weight due to the reduced size of passive components and lower heat generation. The industry trend toward miniaturization, advancements in semiconductor technology, as well as various energy efficiency regulations have made "switcher" the dominant type of PSU across practically the full spectrum of applications. Most PSU manufactured today for AC input applications also include a PFC front end.

In general, SMPS converters can be classified into four types according to the form of input and output voltages: AC to DC (also called off-line DC power supply), DC to DC (voltage or current converter), AC to AC (frequency changer or cycloconverter), and DC to AC (inverter).

2. Objectives:-

The objectives of the project are:-

• Achieve high efficiency (>85%).
• High power factor (>0.95).
• Controlling and monitoring through a computer.
• Universal input voltage.
• Reduce mains noise and harmonics.
• Minimize EMI (electromagnetic interference).
• Implement variable voltage regulation
• Minimize RFI (radio frequency interference).

3. Power Factor:-

Power factor is the ratio of real power to apparent power:-

Real power (watts) produces real work; this is the energy transfer component (example electricity-to-motor rpm).Reactive power is the power required to produce the magnetic fields (lost power) to enable the real work to be done, where apparent power is considered the total power that the power company supplies.

When the power factor is not equal to 1, the current waveform does not follow the voltage waveform. This results not only in power losses, but May also cause harmonics that travel down the neutral line and disrupt other devices connected to the line. The closer the power factor is to 1, the closer the current harmonics will be to zero since all the power is contained in the fundamental frequency.

Since an SMPS uses DC voltage so the mains AC voltage is rectified and filtered, circuit is shown below:-

One problem with SMPS that they do not use any form of power factor correction is that, the input capacitor will only charge when input voltage is close to peak voltage or when input voltage is greater than the capacitor voltage. The capacitor discharges when the input voltage starts going lower than the peak voltage and re-charges when the peak approaches. A capacitor has a very low ESR (electrical series resistance) resulting in very high current when recharging. As a result the current only flows during the peak input voltages resulting in a highly distorted and peaky current waveform having a low power factor. Illustrated in the figure below:-

A switch mode power supply has a power factor of 0.5 to 0.6. Which by any standards is very low. Ideally power factor should be close to 1. With passive PFC, power factor can be improved up to 0.75. With active PFC it can be improved up to 0.99.

4. Active Power Factor Correction (PFC):-

The power factor of an SMPS can be improved by smoothing out the peak currents. The current draw can be averaged out over the whole cycle improving the power factor. In order to do that the input capacitor have to charge over the whole cycle to accumulate energy.

The heart of active PFC is a boost converter. It is placed between the rectifier and input capacitor. So the boost converter receives a fully rectified AC line voltage with no bulk filtering. So the input voltage it receives ranges from zero to peak voltage to zero again. The frequency is twice the line frequency. It boosts the lower voltages to allow the input capacitor to charge during the dips in the input voltage. The boost converter is shown below:-

5. PC Interface:-

In industries all the processes as automated i.e. controlled

by a computer for centralized control. All the sensor data is received by the computer which then further processes the data and acts accordingly. Power supply is the most important component in any electrical or electronic device. It’s monitoring and control is also necessary. It would be really convenient if it can be monitored and controlled through a centralized computer. It would also be easy to implement protections and current limiting through sensor data from the equipment being powered.

For PC interface an arduino would be used as it has an integrated USB interface. The output voltage and current would be monitored and the pulse width in the SMPS controller would be varied according to the voltage and current regulation values.
Related Work:



PCB designing ( simulation and hardware design )

2. 1. Studying Magnetic material
   2. Power electronics
   3. Soldering
   4. Mains voltage safety
   5. Protections
   6. Thermal management.
   7. Arduino development environment.

3. Hardware and Software Requirements:

1. Software:-

1. Lab view.
2. LTsplice
3. Cadsoft eagle
4. Arduino IDE

2. Hardware:-

1. Oscilloscope
2. Multimeter.
3. Dummy load.
4. Power factor meter.
5. Spectrum analyzer (for measuring harmonics).

4. Advantages And Disadvantages of SMPS:-

1. Advantages:

• Much more efficient as compared to linear power supplies because it uses components as switches rather than resistive elements.
• Protection against excessive output voltage by quick acting guard circuits
• Smaller in size and lighter in weight.
• Cheaper at higher power levels (sometimes in lower power as well).
• Regulation is easy and efficient to implement.
• Lower idle power consumption.

1. Disadvantages:-

• The circuit is much more complex as compared to linear PSUs.
• EMI/RFI which is inherent in SMPS is difficult to suppress.
• Electronic noise at the output and input terminals.
• PCB layout is critical.

5. Applications and Future:

Switch mode power supplies have applications in various areas. A switched-mode supply is chosen for an application when its weight, efficiency, size, or wide input range tolerance make it preferable to linear power supplies. Initially the cost of semiconductors made switch-mode supplies a premium cost alternative, but current production switch-mode supplies are nearly always lower in cost than the equivalent linear power supply.

In industrial and high power applications SMPS were not used because semiconductor devices were not rugged enough. But now many manufacturers have made rugged and powerful semiconductor devices. SMPS are now being developed and used in high power application offering cost and space savings.

Project timeline

TASK	Duration	Date
Literature review	1 month	September 2014
Choosing required Hardware	1 month	October 2014
Observation of Hardware	1 month	November 2014
Simulation (software) work	1 month	December 2014
Fabrication of PCB	1 month	January 2015
Installation of Hardware	1 month	February 2015
Testing and Result	1 month	March 2015
Progress Report	1 month	April 2015
Final Thesis	1 month	June 2015
Presentation and Demonstration

References:-

1) Application Note 42047 Power Factor Correction (PFC) Basics – Fairchild semiconductor.click

2) Power factor correction (PFC) handbook HBD853 – ON semiconductorpower factor correction

3) Power Factor Correction (PFC) Parts Selection Guide – Infineon.power factor

4) Control techniques for power factor correction converters - L. Rossetto, G.Spiazzi, P. Tenti

5) Power Supply Cookbook - Marty Brown.

6) Practical Switching Power Supply Design - Marty Brown

7) Switching Power Supply Design - Abraham I PressmenSPSD

8) Switch mode power supply reference manual – ON semiconductorB

BY Hashim Elahi university of engineering and Technology peshawar http://mobilezonex.blogspot.com/2014/02/home-made-switch-mode-power-supply.html