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RD-0613

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and will turn on again at the next zero-crossing of the inductor current as detected by the ZX pin. This

over-current condition can occur, for example, during a low-line condition (Figure 15). As the AC line

decreases, the PFC inductor and MOSFET current will increase to keep the DC bus constant for a

given power level. When the peak current reaches the over-current threshold, the cycle-by-cycle

current limit will cause the peak of the MOSFET current to flatten and the DC bus to start to drop. This

current limit is necessary to prevent saturation of the PFC inductor current and to protect the PFC

MOSFET from being damaged.

Fig. 15: OC Pin Voltage (Black) and DC Bus Voltage (Green) During Low-Line Condition

Brown-Out Protection

The IRS2168D includes an under-voltage reset (UVR) function at the VBUS pin. Should the DC bus

decrease too far during a momentary interrupt of the mains input voltage, the ballast should be properly

shutdown and restarted. This will prevent the lamp from extinguishing and will properly preheat and

restart the lamp when the mains voltage returns. If the VBUS pin voltage decreases below 3 V, the

PFC and half-bridge gate drivers will be turned off and VCC will be discharged to UVLO-. The ballast

will then be restarted via the RSUPPLY resistor when the mains voltage reaches a high enough level

again (Figure 16).