AN10881
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© NXP B.V. 2011. All rights reserved.
Application note
Rev. 2 — 26 September 2011
5 of 102
NXP Semiconductors
AN10881
TEA1713 resonant power supply control IC with PFC
2. TEA1713
highlights and features
2.1 Resonant conversion
Today’s market demands high-quality, reliable, small, lightweight and efficient power
supplies.
In principle, the higher the operating frequency, the smaller and lighter the transformers,
filter inductors and capacitors can be. On the other hand, the core, switching and winding
losses of the transformer increase at higher frequencies and become dominant. This
effect reduces the efficiency at a high frequency, which limits the minimum size of the
transformer.
The corner frequency of the output filter usually determines the bandwidth of the control
loop. A well-chosen corner frequency allows high operating frequencies to achieve a fast
dynamic response.
Pulse Width Modulated (PWM) power converters, such as flyback, up and down
converters, are widely used in low and medium power applications. A disadvantage of
these converters is that the PWM rectangular voltage and current waveforms cause
turn-on and turn-off losses that limit the operating frequency. The rectangular waveforms
also generate broadband electromagnetic energy that can produce ElectroMagnetic
Interference (EMI).
A resonant DC-to-DC converter produces sinusoidal waveforms and reduces the
switching losses, which provide the possibility of operation at higher frequencies.
Recent environmental considerations have resulted in a need for high efficiency
performance at low loads. Burst mode operation of the resonant converter can provide
this if the converter is required to remain active as is the case for adapter applications.
Why resonant conversion?
•
High power
•
High efficiency
•
EMI friendly
•
Compact
2.2 Power factor correction conversion
Most switch mode power supplies result in a non-linear impedance (load characteristic) to
the mains input. Current taken from the mains supply occurs only at the highest voltage
peaks and is stored in a large capacitor. The energy is taken from this capacitor storage,
in accordance with the switch mode power supply operation characteristics.
Government regulations dictate special requirements for the load characteristics of certain
applications. Two main requirements can be distinguished:
•
Mains harmonics requirements EN61000-3-2
•
Power factor (real power/apparent power)
The requirements work towards a more resistive characteristic of the mains load.