Switching vs. Transformer Power: What’s the Difference?

Switched-Mode Power Supply (SMPS)

A switched-mode power supply is a type of power supply that uses electronic switching technology. It maintains a stable output voltage or current by controlling the duty cycle of the switching transistor. There are generally two types: isolated and non-isolated.

SMPS provides multiple protection functions, including over-voltage, over-current, over-temperature, and short-circuit protection.

Working Principle of SMPS

The main components of an SMPS include:

• Rectifier bridge

• MOSFET

• Power management IC

• Schottky rectifier diode

• Feedback optocoupler

• Voltage reference regulator (such as TL431)

Working process:

When the output voltage fluctuates → TL431 detects the change → Signals the feedback optocoupler (817) → Sends feedback to the power management IC → Controls the MOSFET switching time → Stabilizes the output voltage.

Advantages of SMPS

1. High Efficiency & Compact Size
   The high switching frequency of SMPS allows for a very small transformer. Voltage regulation is achieved by adjusting the conduction time of the MOSFET operating in saturation mode. This results in minimal core loss, copper loss, and component loss. Since it only includes electronic components, a PCB, and a small transformer, the power supply is compact and lightweight.

2. Wide Input Voltage Range
   SMPS typically supports input voltages from 90V to 240V, making it suitable for use worldwide.

3. Flexible Input Types
   SMPS supports both AC and DC input, enhancing its adaptability in various applications.

Transformer-Based Power Supply

A transformer-based power supply converts voltage based on the principle of electromagnetic induction, and like SMPS, it also has isolated and non-isolated types.

Working Principle of Transformer Power Supply

1. ☞The main components include:

   • Transformer

   • Bridge rectifier

   • Filtering circuit

   • Voltage regulation circuit

2. ☞The transformer operates on electromagnetic induction, consisting of:

   • Primary coil

   • Secondary coil

   • Magnetic core (iron core)

3. ☞AC power is first stepped up or down by the transformer →
   Then rectified into DC by the bridge rectifier →
   Filtered and stabilized through the filtering and regulation circuits →
   Resulting in a stable DC output.

4. ☞Due to the low mains frequency (typically 50/60Hz), the transformer is large in size, and the filter capacitors require high capacitance.
   As a result, the overall power supply tends to be bulkier and heavier.

Advantages of Transformer Power Supply

5. Low Electromagnetic Interference (EMI)
   Transformer-based power supplies do not easily introduce additional interference. They have very low ripple, which is critical for small-signal analog applications (such as audio sources). Therefore, audiophile-grade audio systems still often rely on transformer-based power supplies.

6. Excellent Surge Protection
   The transformer’s structure—two windings and a magnetic core—naturally suppresses sudden voltage changes. This provides strong resistance against high-voltage surges, offering better lightning protection.

Conclusion

This article outlines and compares the advantages of transformer-based power supplies and switched-mode power supplies (SMPS).

• Transformer power supplies remain preferred in high-end audio equipment due to their low EMI, low ripple, and superior surge resistance.

• Switched-mode power supplies, on the other hand, stand out with their high efficiency, compact and lightweight design, wide input voltage compatibility, and support for both AC and DC input, making them a versatile and modern solution for a wide range of applications.