An air cleaner is provided according to an embodiment of the invention. The air cleaner includes a high voltage power supply configured to provide a high voltage to a collector cell and a shut-down circuit coupled to the high voltage power supply. The shut-down circuit is configured to monitor an electrical current supplied to the collector cell, remove electrical power to the collector cell if the electrical current exceeds a predetermined cell current threshold for a predetermined time period, and generate an indication if the electrical power is removed from the collector cell.