What is SMPS?
SMPS stands for “Switched-Mode Power Supply.” It is a type of power supply used in electronic devices and equipment to efficiently convert and regulate electrical power from one form to another. SMPS is commonly used in computers, laptops, smartphones, televisions, and many other devices that require stable and reliable power.
Unlike traditional linear power supplies, which use a continuous voltage regulator to reduce the voltage, SMPS uses a switching regulator to rapidly switch the input voltage on and off at a high frequency. This switching action allows the SMPS to efficiently step up or step down the voltage, depending on the device’s power requirements.
Block Diagram of SMPS
Working Principle of SMPS
In SMPS, the input ac supply is converted into a very high filtered dc voltage. This dc voltage is given to a switching element which may be transistor or MOSFET.
The switching element is switched ON and OFF at a very high speed by a pulse width modulator. The switching frequency for transistor is 40 kHz and for MOSFET 250 kHz. The switching element generates square pulses at this high frequency. The square wave pulses are applied to the primary of a ferrite core transformer. The voltage at the secondary is rectified and filtered to produce rectified output voltage.
For regulation of output voltage, a part of the output voltage is fed back and applied to an error amplifier which compares it to a reference voltage. An error voltage is generated and it is used to control the ON and OFF ratio of a Pulse Width Modulator. The output voltage from PWM control the switching action of the switching element.
If output voltage increases, the error voltage also increases. This decreases the ON time of the switching element and brings the output to the desired value.
If output voltage decreases, the error voltage decreases. This increases the ON time of the switching element and brings the output to the desired value.
Advantages of SMPS
- Low cost
- Higher efficiency
Disadvantages of SMPS
- The control circuit is less reliable.
- Due to EMI effect, operation of SMPS is disturbed.
Application of SMPS
- Used in Personal Computers
- Used in smartphones also.
Circuit diagram of SMPS
Difference between Linear Power Supply and SMPS
| Parameters | Linear Power Supply | SMPS |
|---|---|---|
| 1. Size | Bulky | Small |
| 2. Efficiency | 25% to 50% | 75% to 95% |
| 3. Noise | Low | High |
| 4. Ripple Voltage | 5 mV | 25 mV to 50 mV |
| 5. Magnetic Material | Laminated Iron | Ferrite Core |
| 6. Reliability | More Reliable | Less Reliable |
| 7. R.F. interference | Absent | Present |
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