| 摘要 |
<p>A thermostatically controlled heater intended primarily for heating water in an aquarium has a two-compartment sealed casing. The upper portion (1) Figure 1 houses an electronic temperature control device, including a thermistor sensor 21 which is responsive to the temperature of liquid surrounding the casing, to control the supply of alternating current from an input cable (5) to a heater element contained in the lower portion (2) of the casing. The control device Figure 2 is transformerless and is therefore relatively compact, but it is powered directly from the a.c. mains input fed via the cable (5). The control device includes a triac 12 controlled by a bridge circuit including the thermistor 21, a set value potentiometer 25, and an a.c. powered integrated circuit, the latter being connected to the mains input by a compact voltage reducer network 16. The triac controls a heater element (not shown) connected to output terminals 13. <IMAGE></p> |
