Series Resonant Converter Design
RESONANT CONVERTERS THE RESONANT CONVERTERS The resonant switching topology is, to date, one of the most efficient solutions for switch mode power supply design. 'Although in existence for many years, only recently has the LLC resonant converter, in particular in its half-bridge implementation, gained in the popularity it certainly deserves. In many applications, such as flat panel TVs, 85+ ATX PCs or small form factor PCs, where the requirements on efficiency and power density of their SMPS are getting tougher and tougher, the LLC resonant half-bridge with its many benefits and very few drawbacks is an excellent solution.' In fact the introduction of new regulations, both voluntary and mandatory, has brought about a revaluation of the LLC series resonant topology. In LED lighting, to name just one of the infinite applications, the need for more and more efficient power supply systems is pushing power designers in this direction.
High Frequency
All the main manufacturers of active components currently available on the SMPS market have included efficient chips in their product catalogues. With an effectively contained degree of circuit complexity, they allow the realisation of power supplies with 90-96% efficiency, (which can be improved further using synchronous rectifiers instead of output diodes) and reduced EMI/EMC problems in comparison to other topologies thanks to the 'Zero Voltage Switching' and to the substantially sinusoidal high frequency currents. 'Generally speaking, resonant converters are switching converters that include a tank circuit actively participating in determining input-to-output power flow.' The operating principle is based on the characteristic gain curve of the resonant tank', which allows to change the gain by a moderate variation of the switching frequency, thus resulting in an effective regulation of output voltage or current in relation to load and input voltage changes. The resonant 'tank' is a set of two inductive elements and one capacitor (LLC). Even if the use of three different components, i.e.
Half Bridge Series Resonant Converter
An introduction to LLC resonant half-bridge. Two of them generate the well-known series resonant converter and. 2 The LLC resonant half-bridge converter. The PMP20795 reference design uses UCC256301 enhanced LLC controller with integrated driver to provide 24V/12A output from a nominal 380VDC input.
A discrete inductor, a conventional transformer and a capacitor is technically possible, poor results would be obtained on all fronts: cost, size and energy efficiency. The use of an integrated transformer is much more convenient, which has specific features and integrates resonant inductance as described below.
To give an idea of the advantages, if a 150 W integrated transformer is well-dimensioned it can have dimensions of less than 28x29x23 mm, with costs that are obviously more competitive with respect to solutions with discrete inductance. It is therefore evident that the only reason that can lead to this solution is the design difficulty of a coherent tank.
While the designs of the largest manufacturers of electronic equipment generally show a correct structuring of the integrated transformer and other inductive components, mid-sized or small manufacturers - even if all SMPS manufacturers enjoy the same technology advantages in relation to active and passive components - very often do not have the same benefits in regards to fundamental components, such as the integrated transformer and PFC stage inductor, given the specificity of the inductive components and the limitation of resources destined to the project.
Description The PMP20795 reference design uses UCC256301 enhanced LLC controller with integrated driver to provide 24V/12A output from a nominal 380VDC input. UCC256301 provides hybrid hysteresis control (HHC) to enable a fast transient response. In this design, a 1st order system with over 6kHz bandwidth is achieved. In addition, the advanced burst mode allows this converter to achieve less than 200mW power consumption at no load. With 200kHz nominal switching frequency, the converter is able to achieve over 96% peak efficiency. Part Number Name Product Family Sample & Buy Design Kits & Evaluation Modules Adjustable Precision Shunt Regulator Voltage Reference Not Available Wide Vin LLC Resonant Controller With High-Voltage Start Up Enabling Ultra-Low Standby Power Offline and Isolated DC/DC Controllers and Converters Wide Vin LLC Resonant Controller With High-Voltage Start Up Enabling Low Standby Power Offline and Isolated DC/DC Controllers and Converters Technical Documents View the covering authorized use, intellectual property matters and disclaimers.