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AN1523 Datasheet(PDF) 10 Page - STMicroelectronics |
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AN1523 Datasheet(HTML) 10 Page - STMicroelectronics |
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10 / 24 page  AN1523 APPLICATION NOTE 10/24 Turn-Off Even at turn off the transition is clean, without any ab- normal behaviour like overshoots or glitches both on the output voltages. Checking the full load condition, a restart attempt is present on the Vcc voltage: it is due to the circuit Q1, Q2,R9, R10, R11, C6 connect- ed to the COMP pin. During the switching off phase the energy in the bulk capacitor is no more refreshed, then the voltage on it starts to decrease. This pro- vides for an increasing of the COMP pin voltage due to the loop intervention which is regulating the output voltage while the input voltage is decreasing. At a certain value the COMP voltage is able to switch on Q1 and then Q2, thus disconnecting the transformer from Vcc, so that the L6590 stops the operation. Be- cause the circuit is switched off externally, the bulk capacitor has still some energy stored and when the Vcc has dropped below the Vccoff the IC detects that residual input voltage higher than its Drain start volt- age (Vdsmin). Hence the L6590 reactivates the inter- nal current source like in a normal start-up, and the voltage on the Vcc pin tends to increase again. But checking the Fig. 17 it is important to note that the Vcc value is far from the Start Threshold voltage (Vc- con), then no any perturbation appears on the output, avoiding any problem.. Figure 16. WAKE UP TIME Vin = 115 Vrms - 50 Hz @FULL LOAD CH1: VPIN1 - DRAIN VOLTAGE CH2: VPIN3 -Vcc CH3: +5VOUT Figure 17. TURN-OFF Figure 18. TURN-OFF Vin = 115 Vrms - 50 Hz @FULL LOAD Vin = 115 Vrms - 50 Hz @STAND-BY CH1: VPIN1 – DRAIN VOLTAGE CH1: VPIN1 – DRAIN VOLTAGE CH2: VPIN3 - Vcc CH2: VPIN3 -Vcc CH3: +5VOUT CH3: +5VOUT |
Similar Part No. - AN1523 |
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Similar Description - AN1523 |
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