Philips 27PS60S321 manual Frequency Behavior, Start-Up Sequence

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zInterval 4:t3 < t < t00 resonance time In thefourth interval, the energy stored in the drain capacitor C D will start to resonatewith the inductance L P .The voltage and current waveforms are sinusoidal waveforms. Thedrain voltage will drop from V IN +n•V OUT to V

IN -n•VOUT .

Frequency Behavior

The frequency in the QR-mode is determinedby the power stage and is not influenced by the controller (important parametersare L P and C D ). The frequency varieswith the input voltage V IN andthe output power P OUT .If the required output power increases, more energy has to be storedin the transformer. This leads to longer magnetizing t PRIM and demagnetizingt SEC times, whichwill decrease the frequency. See the frequency versus output powercharacteristics below. The frequency characteristic is not onlyoutput power-, but also input voltage dependent. The higher theinput voltage, the smaller t PRIM ,so the higher the frequency will be.

Figure:

Point P1 is the minimum frequency f MIN that occurs at the specifiedminimum input voltage and maximum output power required by the application.Of course the minimum frequency has to be chosen above the audiblelimit (>20 kHz).

Start-Up Sequence

When the rectified AC voltage V IN (via the center tapconnected to pin 8) reaches the Mains

7/8/2004