How SMPS works | What Components We Need? Switched Mode Power Supply

Summary

This video provides a clear and detailed explanation of switch mode power supplies (SMPS) and why they outperform traditional linear power supplies. It compares efficiency, size, weight, and cost, showing how SMPS achieve higher performance using high-frequency switching, MOSFET transistors, and smaller ferrite transformers. The video breaks down SMPS into five main blocks—input protection and filter, rectifier and primary filter, switching transistors, transformer and secondary rectifier, and output filter with feedback—explaining the function of each component. Viewers learn how SMPS convert AC to stable DC efficiently, maintain regulated output through feedback, and why these supplies are compact, lightweight, and versatile for modern applications.

Takeaways

• ⚡ Switch Mode Power Supplies (SMPS) are highly efficient, converting AC to DC while regulating voltage and current for specific projects.
• 🏋️ SMPS are much lighter and smaller than linear power supplies, even for higher wattages, due to the use of high-frequency transformers.
• 🔥 Linear power supplies are inefficient, losing power as heat in transformers and regulators, and become bulky for higher loads.
• 🔄 Linear transformers operate at low frequencies (50–60 Hz), requiring heavy metal cores and thick copper windings.
• 🔧 SMPS use MOSFETs switching at high frequencies (>20 kHz) to reduce energy losses and allow smaller transformer designs.
• 🧩 A basic SMPS consists of five blocks: input protection & EMC filter, rectifier & primary filter, switching transistors, transformer & rectifier, and output filter with feedback.
• 🛡️ Input protection includes fuses and EMC filters to remove high-frequency noise and protect the circuit.
• ⚡ The rectifier and primary filter convert AC to pulsating DC and smooth it with capacitors, typically producing ~320V DC from 230V AC in Europe.
• 🔁 Switching transistors (MOSFETs) create high-frequency pulses controlled by a PWM IC, which the transformer steps down to the desired voltage.
• 🔧 Output filters (LC) smooth the rectified pulses, while feedback via optocouplers maintains stable voltage and current.
• 💡 Advanced SMPS designs may include power factor correction, multiple outputs, and enhanced safety and feedback features.
• 🏆 Overall, SMPS offer higher efficiency, lower weight, smaller size, and better voltage control compared to traditional linear power supplies.

Q & A

What does SMPS stand for, and what is its primary function?

SMPS stands for Switch Mode Power Supply. Its primary function is to convert AC voltage to DC voltage while efficiently adjusting the voltage and current as needed for specific applications.

How does an SMPS differ from a linear power supply in terms of efficiency and weight?

An SMPS is much more efficient, lighter, and smaller than a linear power supply because it operates at high frequencies, uses smaller transformers, and dissipates less heat, whereas linear supplies rely on heavy low-frequency transformers and linear regulators that lose energy as heat.

Why are linear power supplies heavy and inefficient?

Linear power supplies are heavy and inefficient because they use low-frequency transformers requiring large cores and many copper windings, and linear regulators dissipate excess power as heat, which increases weight, size, and cost.

What are the five main blocks of a basic SMPS?

The five main blocks of a basic SMPS are: (A) Input protection and EMC filter, (B) Full bridge rectifier and primary filter, (C) Switching transistors with PWM controller, (D) Transformer with secondary rectifier diodes, and (E) Output filter with feedback for voltage regulation.

What is the role of the EMC filter in an SMPS?

The EMC filter removes high-frequency noise from the input AC voltage, ensuring a clean signal before it is rectified, which prevents interference and improves the stability of the power supply.

How do MOSFETs contribute to the efficiency of an SMPS?

MOSFETs operate in switching mode, spending most of their time either fully on (saturation) or fully off (cut-off), which minimizes power dissipation and allows the SMPS to achieve high efficiency.

Why can SMPS transformers be much smaller than linear transformers?

SMPS transformers operate at high frequencies (often above 20 kHz), allowing the use of smaller ferrite cores and shorter windings because inductance requirements are lower at high frequency, reducing size and weight.

What is the purpose of the feedback mechanism in an SMPS?

The feedback mechanism monitors the output voltage (and sometimes current) and sends a signal to the PWM controller to adjust the duty cycle of the MOSFETs, ensuring a stable and accurate output voltage regardless of load variations.

How does the secondary LC filter in an SMPS smooth the output?

The secondary LC filter uses an inductor and capacitor to smooth the rectified high-frequency pulses, charging and discharging quickly to produce a steady DC voltage with minimal ripple.

What are some additional features that high-performance SMPS units may include?

High-performance SMPS units may include multiple output voltages, additional feedback loops, power factor correction circuits, and extra transformers to power digital or low-voltage circuits while maintaining safety and insulation.

Why are Schottky diodes used in SMPS instead of standard diodes?

Schottky diodes have lower forward voltage drop and faster switching times, which makes them ideal for rectifying high-frequency signals efficiently, minimizing power loss in SMPS designs.

How does the high-frequency AC signal generated by MOSFETs become a usable DC voltage?

The high-frequency AC signal from the MOSFETs is applied to a pulse transformer, then rectified by Schottky diodes, and finally filtered by an LC network to produce a smooth DC voltage suitable for powering devices.