AN3339 datasheet(24/44 Pages) STMICROELECTRONICS

24 / 44 page

Functional check

AN3339

24/44

Doc ID 18449 Rev 2

cause IC shutdown, therefore providing the system with immunity to short duration

phenomena. If, instead, the overload condition continues, the mentioned procedure for

shutting down the L6599A is activated. Figure 42, 43, and 44 show dead short events on 24

V, 12 V, and 130 V outputs respectively; the voltage on ISEN reaches the second

comparator threshold, the L6599A immediately shuts down and the operation is resumed

after an off-on cycle.

Figure 45 and 46 show the OVP intervention. In the case of overvoltage of one or more of

the resonant outputs the Zener diodes D16, D17, and D29 detect the output voltages and

conduct. Then Q10 conducts and turns on Q9 too. These two transistors are configured as

an SCR that shorts to ground the anode of the U5 optocoupler. In this way the Q7 is no

longer delivering the Vcc to the controllers and stays permanently latched until the mains

voltage is recycled.

Figure 41.

24 V current limitation at full load

and 115 Vac - 60 Hz

Figure 42.

24 V short-circuit at full load and

115 Vac - 60 Hz

CH3: ISEN

CH1: 24 V o/p voltage CH2: CSS

CH4: 24 V o/p current

CH3: ISEN

CH1: LVG

CH2: DELAY

CH4: 24 V o/p current

Figure 43.

12 V short-circuit at full load and

115 Vac - 60 Hz

Figure 44.

130 V short-circuit at full load and

115 Vac - 60 Hz

CH3: ISEN

CH1: LVG

CH2: DELAY

CH4: 24 V o/p current

CH3: ISEN

CH1: LVG

CH2: DELAY

CH4: 24 V o/p current

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