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NCP1615 Datasheet(PDF) 22 Page - ON Semiconductor |
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NCP1615 Datasheet(HTML) 22 Page - ON Semiconductor |
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22 / 44 page  NCP1615 http://onsemi.com 22 Figure 18. Current Sense and Zero Current Detection Blocks VOCP S R Q DRV OCP OverStress ZCD signal for valley detection and CCFF CS/ZCD Rsense DRV Q1 D1 CBULK CIN Current Limit Comparator LEB tOVS(LEB) RCS RZCD1 RZCD2 DZCD Vin Vout ACin ZCD Comparator VZCD(rising)/ VZCD(falling) Overstress watchdog timer (toff2) LEB tOCP(LEB) PFCOK SIGNAL The PFCOK pin provides a dedicated 5 V reference when the PFC stage is in regulation. The pin is internally grounded during the following conditions: • During Start−Up: It remains low until the output voltage achieves regulation and the voltage stabilizes at the right level. • Low Output Voltage: If the PFC stage output voltage is below the bulk undervoltage (BUV_Fault) level, this is indicative of a fault. The PFCOK signal then provides a means to disable and protect the downstream converter. • Brownout fault is detected (after discharge of control capacitor). • Low supply voltage: VCC falls below VCC(off). • Feedback undervoltage fault. • Fault condition: A fault detected through the Fault pin. • Open FB pin. • Thermal Shutdown. • Line voltage removal. The circuit schematic of the PFCOK block is shown Figure 19. Figure 19. PFCOK Circuit Schematic PFC_OK R S Q Dominant Reset Latch Q PFCOK OVLflag OFF BUV_fault Line_OVP In_Regulation The PFCOK circuit monitors the current sourced by the OTA. The OTA current reaches zero when the output voltage has reached its nominal level. This is represented in the block diagram by the “In_Regulation” Signal. The PFCOK signal goes high when the current reaches zero or falls below zero. The start−up phase is then complete and the PFCOK signal goes high until a fault is detected. Another signal considered before setting the PFCOK signal is the BUV. The PFCOK signal will remain low until the bulk voltage is above the undervoltage threshold. The PFCOK signal will go low if the bulk voltage drops below its undervoltage threshold. BROWNOUT DETECTION The HV pin provides access to the brownout and line voltage detectors. It also provides access to the input filter capacitor discharge circuit. The brownout detector detects main interruptions and the line voltage detector determines the presence of either 110 V or 220 V ac mains. Depending on the detected input voltage range device parameters are internally adjusted to optimize the system performance. Line and neutral are diode “ORed” before connecting to the HV pin as shown in Figure 20. The diodes prevent the pin voltage from going below ground. A low value resistor in series with the diodes can be used for protection. A low value resistor is needed to reduce the voltage offset while sensing the line voltage. Figure 20. High−Voltage Input Connection EMI AC IN HV Controller FILTER The controller is enabled once VHV is above the brownout threshold, VBO(start), typically 111 V, and VCC reaches VCC(on). Figure 21 shows typical power up waveforms. |
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Similar Description - NCP1615 |
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