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IRS2166DSPBF Datasheet(PDF) 13 Page - International Rectifier |
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IRS2166DSPBF Datasheet(HTML) 13 Page - International Rectifier |
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13 / 20 page  IRS2166D(S)PbF www.irf.com Page 13 0 0 I LPFC PFC pin near peak region of rectified AC line near zero-crossing region of rectified AC line Fig. 12: On-time modulation near the zero-crossings decrease below the internal 4.0 V threshold (VBUSREG), a watch-dog pulse is forced on the PFC pin and normal PFC operation is resumed. Undervoltage Reset (UVR) When the line input voltage is decreased, interrupted or a brown-out condition occurs, the PFC feedback loop causes the on-time of MPFC to increase in order to keep the DC bus constant. Should the on-time increase too far, the resulting peak currents in LPFC can exceed the saturation current limit of LPFC. LPFC will then saturate and very high peak currents and di/dt levels will occur. To prevent this, the maximum on-time is limited by limiting the maximum voltage on the COMP pin with an external zener diode DCOMP (Fig. 8). As the line input voltage decreases, the COMP pin voltage and therefore the on- time will eventually limit. The PFC can no longer supply enough current to keep the DC bus fixed for the given load power and the DC bus will begin to drop. Decreasing the line input voltage further will cause the VBUS pin to eventually decrease below the internal 3 V threshold (VBUSUV) (Fig. 9). When this occurs, V CC is discharged internally below VCCUV-, the IRS2166D enters UVLO mode and both the PFC and ballast sections are disabled (see State Diagram). The start-up supply resistor to V CC, together with the micro-power start-up current of the IRS2166D, determines the line input turn- on voltage. This should be set such that the ballast turns on at a line voltage level above the undervoltage turn-off level, VCCUV+. It is the correct selection of the value of the supply resistor to V CC and the zener diode on the COMP pin that correctly program the on and off line input voltage thresholds for the ballast. With these thresholds correctly set, the ballast will turn off due to the 3.0 V undervoltage threshold (VBUSUV) on the VBUS pin, and on again at a higher line input voltage (hysteresis) due to the supply resistor to V CC. This hysteresis will result in a proper reset of the ballast without flickering of the lamp, bouncing of the DC bus or re-ignition of the lamp when the DC bus is too low. PFC Over-Current Protection In case of fast on/off interruptions of the mains input voltage or during normal lamp ignition, the DC bus voltage level can decrease below the instantaneous rectified line voltage. Should this occur, the PFC inductor current and PFC MOSFET current can increase to high levels causing the PFC inductor to saturate and/or the PFC MOSFET to become damaged. During fast on/off interruptions of the input mains voltage, the DC bus can drop during the time when the mains voltage is interrupted (off). Since VCC is still above UVLO-, the IC will continue to operate and will increase the COMP pin voltage to increase the PFC MOSFET on-time due to the dropping of the DC bus. When the mains voltage returns again quickly, (before VCC reaches UVLO-), the on-time of the PFC MOSFET is too long for the given mains voltage level resulting in high PFC inductor and MOSFET currents that can saturate the inductor and/or damage the PFC MOSFET (Fig. 13). Fig. 13 : High PFC inductor current during fast mains on/off (upper trace: DC Bus, 100 V/div; middle trace: AC line input voltage, 100 V/div; lower trace: PFC inductor current 1 A/div). During lamp ignition, the DC bus can drop below the rectified AC line voltage causing current to conduct directly from the output of the rectifier, through the PFC inductor and diode, to the DC bus capacitor. This results in a low-frequency offset of current in the PFC inductor. Since the zero-crossing detection circuit only detects the high-frequency zero-crossing of the inductor current, the PFC MOSFET will turn on again each cycle before the inductor current has reached zero. This causes the PFC to work in a continuous conduction mode and the sum of the low-frequency and high-frequency components of current can saturate the PFC inductor and/or damage the PFC MOSFET. To protect against these conditions, a current sense resistor (RS) can be inserted between the source on the PFC MOSFET and ground, and a diode (D4) connected from the top of this current sensing resistor to the VBUS pin (Fig. 14). |
Similar Part No. - IRS2166DSPBF |
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Similar Description - IRS2166DSPBF |
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