The different types of SMPS include the following
- D.C. to D.C. Converter
- Forward Converter:
- Flyback Converter
- Self-Oscillating Flyback Converter
The main power received from the AC main is resolved and filtered as high voltage DC. Then, it is changing at an enormous rate of speed and fed to the main side of the step-down transformer. This transformer is only a segment of the size of an equivalent 50 Hz unit, thus releasing the size and weight problems. The filtered and rectified o/p at the minor side of the transformer. Then it is now sent to the o/p of the power supply. A sample of this o/p is sent back to the button to control the o/p voltage.
In a forward converter, the choke transmits the current when the transistor is leading as well as when it is not. The diode transmits the current through the OFF period of the transistor. Thus, the flow of current into the load during both the periods. The choke stores energy during the ON period and also permits some energy into the o/p load.
In this converter, the magnetic field of the inductor supplies the energy throughout the ON period of the switch. The energy is collapsed into the o/p voltage circuit when the button is in the open state. The duty cycle controls the output voltage.
Self-Oscillating Flyback Converter
This is the most simple converter based on the principle of the flyback. Throughout the conduction time of the switching transistor, the flow of current through the transformer primary switches ramping up linearly with the angle equal to Vin/Lp. The induced voltage in the secondary winding and the feedback winding make the fastest recovery rectifier reverse biased and hold the conducting transistor ON. When the primary current touches a peak value ‘Ip’, where the core activates to saturate, the current inclines to increase very sharply. This cannot be supported by the fixed base drive offered by the feedback winding. As a result, the switching activates to come out of saturation.
Features between SMPS and Linear power Supply
|Features||Linear Power Supply||SMPS|
|Efficiency||25-50 %||65-75 %|
|Ripple value||Even 5 mV possible||Higher 25-50 mV|
|Overall regulation||0.1 %||0.3 %|
|RF interference||None||Can cause problem if not properly shielded|
|Magnetic material||Stalloy or CRGO core||Ferrite core|
|Weight||20-30 W\kg||About 60 W\kg|
|Reliability||More reliable||Depends on the switches|
|Transient response||Faster||Slower (in ms)|
Advantages and Disadvantages
- The main advantage of the SMPS is greater efficiency than linear regulators because the switching transistor dissolves little power when working as a switch.
- The size of SMPS is a smaller size and lighter in weight from the removal of heavy line frequency transformers, and similar heat generation. The standby power loss is frequently much less than transformers.
- Disadvantages of SMPS include better complexity, the generation of high-amplitude, the high-frequency energy that the LPF must block to avoid EMI (electromagnetic interference), harmonic frequencies, and a ripple voltage at the switching frequency.
- The low-cost SMPSs may pair electrical switching noise back onto the main power line, causing interference with equipment connected to the similar phase. Non-power factor corrected power supplies also source harmonic distortion.