SUNLAMP DELAYED EXTINCTION CIRCUIT

摘要

The invention relates to a sunlamp device which is provided with a high pressure mercury vapour discharge tube and with an auxiliary device for extinguishing the discharge tube with a given time delay on termination of the desired irradiation period. According to the invention a switch connected in series with the discharge tube is shunted by a resistor having a positive temperature coefficient of resistance (PTC resistor). This ensures that after the switch has been opened on termination of the desired irradiation period the PTC resistor passes current for some time. As a result the resistance of this PTC resistor is increased, which causes the current through the discharge tube to be reduced. This finally results in an increase of the operating voltage of the discharge tube to a value higher than the available voltage, so that the -tube is extinguished. This device is simpler than a known device provided with two timers.