An overvoltage protection circuit is for a circuit of an output MOS transistor and a load connected in series between a first power supply and a second power supply. Magnetic dish sets can include a dish body having a bottom area releasably attachable to a base. The electrode assembly also has an electrode hull for at least partially surrounding the support hull and a portion of the lead adjacent to the support hull. The collect device, used to collect smoke, can precisely control a pumping smoke time and a pumping smoke capacity by introducing a step motor. The present invention also provides a method of magnetizing the shaft of such a motor and a fixture and method of manufacturing the fixture therefor.