| 摘要 |
A heater for a heating pad uses heating elements of positive temperature coefficient (PTC) material arranged in parallel between a conductor connected through a fuse (5) to an ungrounded pole of electric a.c. mains and a conductor connected through a triac switch (T1) to a grounded pole of the a.c. Both of these conductors have safety link extensions for providing to a micro-controller integrated circuit (14). When a fault occurs such as a break in a conductor in or near the heater, (PTC) a neon breakdown tube connected to the safety link extension of the ungrounded conductor quickly extinguishes for lack of voltage. Other faults are detected by the grounded conductor extension which has a voltage divider to ground. An a.c. signal from its tap controls a transistor (Q1) which is pulsed ON when the transistor (Q1) is not biased OFF because of a fault. |
