Benefits and drawbacks of the LLC Resonant Power Supplies

The resonant topology is, to this day, one of the most efficient for designing SMPS:

The market requiring more efficiency in the areas of LED lighting, server farms, gate automation, battery chargers, vending machines, etc. is a widely known fact.
Besides the marketing driven requirements, many standards impose higher and higher efficiency targets.
This lead to a great revaluation of the LLC (and in some cases LCC) resonant topology in the last few years.
All the major active components manufacturers on the SMPS market have therefore developed controllers allowing the realization of high efficiency converters with low EMI  emissions, with a particularly low circuit complexity.

– efficiency around 94-96% in the simplest circuit solutions, with the possibility of improvement through synchronous rectification and/or other precautions;
– using correctly designed magnetic components, the design is very quick and simplified;
– high frequency currents wave shapes are substantially sinusoidal, with a very limited harmonic content compared to other topologies;
– “ZVS” (zero voltage switching) of MOSFETs that causes a dramatic reduction of losses, reduction/elimination of the heatsink and reduction of stress and generated disturbances, which often cause the most unpredictable and hostile design problems;
– possibility of low power at light load/stand by using the “burst mode” and “PFC stop” functions implemented on many controllers;
– possibility of optimal design for continuous and temporary power even very distant from each other (e.g. our transformer with a size equal to that of a classic EF25 can arrive up to a 500-1000W peak power);
– compared to other topologies, as a result of the previous points, LLC-LCC power supplies have small size and considerably reduced EMI problems.

Critical issues
– optimal designing of the SMPS must necessarily consider also the constraints linked to magnetic components, otherwise it may result in a considerable efficiency reduction.
– the definition of the optimized integrated transformer requires specific skills;
– the necessity of 2 MOSFETs (half bridge) compared to the single MOSFET in flyback converters;
– slightly more expensive controller compared to a flyback converter, but thanks to the lower spending for heatsinks, EMC filter, more compact transformer, etc., the total cost is low for        powers exceeding 40-50W;

If you want to see some of the simplest circuit solutions and the related comparative tests, open the links below:

Original demo boards

Improved demo boards

Our expertise
We can supply standard transformers with already correctly designed resonant tanks, study optimized variants of these tanks and collaborate with the electronic designer defining custom resonant tanks in order to resolve every specific need.
We invested a lot for the capability of giving a quick and reliable technical support.
With the acquired experience and the support of internally developed proprietary software, we are able to design taking into account skin effect, proximity effect, etc., as well as all the structural constraints.

Do not waste your resources:
Even a well-made power supply project is often widely optimizable when reviewed with our proprietary algorithms.
They take into account at the same time the relationships between the various parameters, all the structural constraints and the losses in the tank elements, in particular the magnetic ones, allowing, as widely demonstrated, the highest level of optimization.
Our support to the electronic designer in the initial phases allows, in addition to a drastic reduction in development time, the best results in terms of efficiency, temperatures, costs and dimensions.

The integrated transformer
This definition refers to a transformer with an integrated resonance inductance obtained through controlled magnification of the leakage inductance (see our technical article published on various european industrial electronic magazines: english, german).
Our standard transformers series covers the most common voltage and power requirements.
To this day converters that, for design simplification, use a discrete inductor in addition to the conventional transformer are still quite common, but this choice is inefficient under economic, energy and dimensional aspects.
We can quickly design and sample custom integrated transformers optimized by design. The need for reiterations and resampling is practically non-existent.