Push-Pull Converter: Advantages and Disadvantages

This page explores the advantages and disadvantages of Push-Pull DC-DC converters, including their circuit design and operational principles.

What is a Push-Pull Converter?

About DC-DC Converters

A DC-DC converter is an electronic circuit whose primary function is to modify one potential difference (voltage) level to another. It essentially acts as a voltage regulator using switches, inductors, and capacitors for power conversion. DC-DC converters have numerous applications and are classified based on isolation between input and output circuits:

• Isolated DC-DC converter
• Non-isolated DC-DC converter

Isolated DC-DC converters are further divided into subtypes:

• Flyback
• Forward
• Half-bridge
• Full-bridge
• Push-Pull

Push-Pull Converter Circuit and Operation

The following image depicts a typical Push-Pull converter circuit:

A Push-Pull converter utilizes a “push-type” and “pull-type” device configuration. The term “Push-Pull” refers to two switches, each connected to either the positive or negative leg of the DC power supply. It’s a widely used DC/DC chopper due to efficient power handling, minimizing power loss at the switching devices.

Key Features of Push-Pull Converters

• Simple and Compact Gating: Push-Pull converters have straightforward gating requirements, using only two devices in the primary section with a common ground.
• Reduced Noise: They generate less noise on the input line, offer stable input current, and are more efficient in high-energy applications.
• HF Transformer Isolation: High-frequency transformer isolation allows for larger step-up ratios and provides galvanic isolation between utility and modules.
• Voltage-Fed vs. Current-Fed:
  • Voltage-fed schemes require large electrolytic capacitors to manage significant input current ripple, leading to larger volumes, higher costs, and a shorter lifespan for PV systems.
  • Current-fed schemes offer advantages over voltage-fed topologies:
    1. Lower input current ripple
    2. Smaller transformer turns-ratio
    3. Simplified output capacitive filter
    4. No flux imbalance issues
• Current-Fed Challenges: Current-fed choppers experience elevated voltage peaks across the switches during switch-off. Passive RCD snubbers are used to absorb the voltage spike, but this reduces efficiency. Non-dissipative snubbers can recycle absorbed power, but increase circuit complexity.
• Active Clamping: Active clamping is a popular technique that achieves high efficiency and zero-voltage/zero-current switching (ZVZCS) for the devices.
• Voltage Doublers: Voltage doublers can be used to reduce the transformer turns ratio and switch voltage requirements.

Advantages of Push-Pull Converters

Here are the benefits of using a Push-Pull converter:

• No Isolated Power Supply Needed for MOSFETs: Driving MOSFETs in a Push-Pull configuration doesn’t require an isolated power supply.
• Peak Current Sensing: Peak current sensing is necessary to prevent the core from drifting into saturation.
• Versatile Applications: Push-Pull systems are used in various applications like freeway access latch release cables and security break cables.
• Flexible Cables: 7V nineteen cables offer excellent flexibility, making them ideal for pull assemblies.
• Low Cost: Push-Pull converters are generally cost-effective.
• Smaller Transformer Rating: The required transformer rating is smaller compared to a forward converter.

Disadvantages of Push-Pull Converters

Here are the drawbacks of using a Push-Pull converter:

• Flux Walking Phenomena: Push-Pull converters utilize two switches, which are more susceptible to flux walking phenomena.
• Central Tap Transformer: The requirement for a central tap transformer is a significant disadvantage.

Conclusion

Understanding the advantages and disadvantages of Push-Pull converters is crucial for making informed design decisions. By weighing these factors against the specific requirements of an application, engineers can determine if a Push-Pull converter is the optimal choice.