Philips 27PS60S321 manual Spms

SPMS Page 18 of 32

dependent operation level(Mlevel: between 60 and 100 V), the internal ‘Mlevel switch’ willbe opened and the start-up current source is enabled to charge capacitorC2521 at the V CC pinas shown below.

The ‘soft start’ switch is closed whenthe V CC reachesa level of 7 V and the ‘soft start’ capacitorC SS (C2522, betweenpin 5 and the sense resistor R3526), is charged to 0.5 V. Once the V CC capacitoris charged to the start-up voltage V CC-start(11V), the IC starts driving the MOSFET. Both internal current sourcesare switched ‘off’ after reaching this start-up voltage.Resistor R SS (3524)will discharge the ‘soft start’ capacitor, suchthat the peak current will slowly increase. This to prevent ‘transformerrattle’.

During start-up, the V CC capacitorwill be discharged until the moment that the primary auxiliary windingtakes over this voltage.

Figure:

The moment that the voltage on pin 1 drops below the ‘under voltagelock out‘ level (UVLO = ± 9 V), the ICwill stop switching and will enter a safe restart from the rectifiedmains voltage.

7/8/2004