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NCP1608 Datasheet(PDF) 19 Page - ON Semiconductor |
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NCP1608 Datasheet(HTML) 19 Page - ON Semiconductor |
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19 / 24 page  NCP1608 http://onsemi.com 19 Overvoltage Protection (OVP) The low bandwidth of the feedback network causes active PFC stages to react to changes in output load or input voltages slowly. Consequently, there is a risk of overshoots during startup, load steps, and line steps. For reliable operation, it is critical that overvoltage protection (OVP) prevents the output voltage from exceeding the ratings of the PFC stage components. The NCP1608 detects excessive output voltages and disables the driver until Vout decreases to a safe level, which ensures that Vout is within the PFC stage component ratings. An internal comparator connected to the FB pin provides the OVP protection. The OVP detection voltage is calculated using Equation 13: Vout(OVP) + VOVP VREF @ VREF @ Rout1 @ Rout2 ) RFB Rout2 @ RFB ) 1 (eq. 13) Where VOVP/VREF is the OVP detection threshold. The value of Cbulk is sized to ensure that OVP is not inadvertently triggered by the 100 Hz or 120 Hz ripple of Vout. The minimum value of Cbulk is calculated using Equation 14: Cbulk w Pout 2 @ p @ Vripple(peak−peak) @ fline @ Vout (eq. 14) Where Vripple(peak-peak) is the peak−to−peak output voltage ripple and fline is the ac line frequency. Vripple(peak-peak) is calculated using Equation 15: Vripple(peak−peak) t 2 @ Vout(OVP) * Vout (eq. 15) The OVP logic includes hysteresis (VOVP(HYS)) to ensure that Vout has sufficient time to discharge before the NCP1608 attempts to restart and to ensure noise immunity. The output voltage at which the NCP1608 attempts a restart (Vout(OVPL)) is calculated using Equation 16: Vout(OVPL) + VOVP VREF @ VREF * VOVP(HYS) @ Rout1 @ Rout2 ) RFB Rout2 @ RFB ) 1 (eq. 16) Figure 43 depicts the operation of the OVP circuitry. Figure 43. OVP Operation OVP Fault DRV Vout(OVPL) Vout(OVP) Vout Undervoltage Protection (UVP) When the input voltage is applied to the PFC stage, Vout is forced to equate to the peak of the line voltage. The NCP1608 detects an undervoltage fault if Vout is unusually low, such that VFB is less than VUVP . During an UVP fault, the drive and error amplifier are disabled. The UVP feature protects the system if there is a disconnection in the power path to Cbulk (i.e. Cbulk is unable to charge) or if Rout1 is disconnected. The output voltage that causes an UVP fault is calculated using Equation 17: Vout(UVP) + VUVP @ Rout1 @ Rout2 ) RFB Rout2 @ RFB ) 1 (eq. 17) Open Feedback Loop Protection The NCP1608 features comprehensive protection against open feedback loop conditions by including OVP, UVP, and FPP. Figure 44 illustrates three conditions in which the feedback loop is open. The corresponding number below describes each condition shown in Figure 44. 1. UVP Protection: The connection from Rout1 to the FB pin is open. Rout2 pulls down the FB pin to ground. The UVP comparator detects an UVP fault and the drive and error amplifier are disabled. 2. OVP Protection: The connection from Rout2 to the FB pin is open. Rout1 pulls up the FB pin to Vout. The ESD diode clamps the FB voltage to 10 V and Rout1 limits the current into the FB pin. The OVP comparator detects an OVP fault and the drive is disabled. |
Similar Part No. - NCP1608_10 |
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Similar Description - NCP1608_10 |
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