A simple, high efficient Flyback converter for complex applications

Increasing the power density of switch-mode power supplies (SMPS) continues to be driven by the lack of space and increased efficiency requirements.  This trend is evident in the commercial, solar and military market sectors as well as medical.  A low component count in a power supply will facilitate the increase in power density.  One SMPS topology that provides a reduction in the number of components is the flyback converter.  This versatile converter has the ability to boost or buck the input voltage depending on the duty cycle.  The flyback topology is well known for its simple  approach and reduced components.  The flyback converter which uses only one magnetic element and one rectifier is used in both AC/DC and DC/DC power conversion which provides galvanic isolation between the input and output.

LED lighting and laser diodes benefit from the flyback SMPS because of its cost-effective approach to furnishing.  These applications sometimes requires a standalone power supply to operate in the range of 30W to 60W.    Characteristics such as isolation, low total harmonic distortion, constant output current, short circuit protection, open circuit protection, and electromagnetic interference (EMI) compliance are necessary for LED and laser diode applications.

A potential challenge with a flyback converter is that high leakage inductance in the flyback transformer generates high voltage spikes and ringing oscillations due to the parasitic resonance between the primary switch parasitic capacitance and the leakage inductance.  The ringing and voltage spikes could damage the main transistor switch when turned off.  Conventional snubbers or clamps are typically employed to protect the primary switch.  Snubbers can be dissipative and some are non-dissipative.  Recovering this leakage energy from the snubber circuit back to the input or DC bus will help improve the efficiency of the flyback.   Other improvements to a flyback topology can be found by replacing the output diode with a synchronous rectifier for low voltage and high current applications. 

Various exclusive topologies using a combination of the flyback and forward converters have been presented in the literature.  A common goal for these various SMPS circuits is to improve efficiency.  However, the improved efficiency with these novel converters comes at the expense of reduced power density and more complexity.  Increasing the component count could potentially negatively impact the reliability of a power supply.

Through our research and development efforts, engineers at Design Criteria, Inc. (DCI) have developed a cost effective, low component count, flyback converter.  This improved converter has many great features not available in present flyback SMPS.  DCI is naming this topology the self-oscillating flyback converter (SOFC). 

The SOFC is not controlled by off-the-shelf SMPS controllers.  However, it utilizes a proprietary self-oscillating controller to drive the primary and secondary switches which is a principal characteristic in simplifying power supplies and reducing the parts count.  Enhanced reliability is also an important benefit of this self-oscillating circuit.  For off-line applications, the oscillator is capable of starting simply by charging a capacitor from the high voltage rectified line.  This avoids power loss in startup resistive elements.

Through our research projects, engineers at Design Criteria, Inc. (DCI) have developed a cost effective, low component count flyback converter.  This novel topology has many key features not available in present SMPS using a flyback topology.  DCI is naming this topology the self-oscillating flyback converter (SOFC).

Applications for this novel DC-DC converter include:

Compact LED Driver

  • ► Consumer electronics
  • ► Military power supplies
  • ► Handheld devices
  • ► Portable Electronics
  • ► LED lighting
  • ► Medical devices

 

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