Introduction
In our previous articles, we explored the fundamentals of power conversion in An Insight into Power Topologies and Design Considerations and Non-Isolated Switching Power Supplies — Topologies & Use Cases, where we discussed the core concepts behind switching power supplies.
Building on that foundation, this article shifts focus to:
Isolated Switching Power Supplies —
Isolated switching power supplies use a high-frequency transformer to create electrical isolation between the input and output. This isolation not only enhances safety but also expands design flexibility, making these solutions suitable for a wide range of applications, from compact consumer electronics to high-power industrial and server systems.
Throughout this article, we’ll explore the different isolated topologies, their unique design characteristics, and how they strike a balance between efficiency, application scope, and power levels.
1. Flyback Topology
- Power Range: Suitable for low-power applications (<100W)
- Function: They can be seen as a Buck-Boost converter with a transformer, providing both voltage conversion and transformer isolation.
- Key Features: Simple structure, ideal for low-power applications like phone chargers and standby supplies.
- Versatility: Supports both AC-DC and DC-DC conversion.
2. Forward Topology
- Power Range: ~50W to 300W
- Function: The Forward converter is a DC-DC converter that uses a transformer, allowing the output voltage to be higher or lower than the input voltage (depending on the transformer’s turns ratio) and providing electrical isolation between the power supply and the load.
- Key Features: Direct energy transfer to the load, commonly used in medium-power applications such as communication devices and industrial power systems.
3. Half-Bridge Topology
- Power Range: ~100W to 500W
- Function: The Half-Bridge is a DC-AC step-down converter and is a “two-quadrant converter” because the load current can flow in both directions. As with the Buck converter, the input current is discontinuous, requiring an input capacitor to compensate for line inductance and handle the higher frequency components of the input current.
- Key Features: Offers higher conversion efficiency and is widely used in servo drives, LCD TV power supplies, and other medium-to-high power systems.
4. Full-Bridge Topology
- Power Range: Typically >500W
- Key Features: Designed for high-power systems such as server power supplies and UPS systems.
- Structure: Two Half-Bridges can form a Full-Bridge topology, which can generate an AC output from a single voltage source without the need for a neutral line.
- Benefit: Achieves the highest transformer utilization efficiency and the highest output power among standard converter topologies.
5. LLC Resonant Converter
- Key Features: Uses resonance-based technology to significantly reduce switching losses, boosting overall efficiency.
- Structure: The LLC Resonant Converter is a DC-DC switching power supply that utilizes a resonant circuit of inductors and capacitors to efficiently convert energy at a defined frequency.
In an LLC Resonant Converter, two inductors and one capacitor are connected in series, with the load connected in parallel with one of the inductors. - Application: Commonly used in servo drives and high-efficiency power supplies.
Other special topologies
In addition to linear and switching power supplies, there are other special topologies, including,
- Bidirectional Buck-Boost topologies that can transfer energy in both directions, making them suitable for energy storage systems such as battery charge/discharge management.
- The Zeta converter is similar to the SEPIC but maintains the same output polarity as the input.
- The H-Bridge is commonly used in motor drives, such as brushless motor control.
Conclusion
Isolated switching power supplies play a vital role in modern electronics, offering both safety and design flexibility across a wide range of power levels and applications. From simple Flyback converters to high-efficiency LLC resonant designs, each topology serves a unique purpose in balancing performance, cost, and complexity.
In our upcoming article, we’ll take a closer look at the key considerations for choosing the right power topology to suit your specific design needs.
Related Article
An Insight into Power Topologies and Design Considerations
Non-Isolated Switching Power Supplies — Topologies & Use Cases