| 摘要 |
PURPOSE:To reduce generation of an arc current by so switching as to connect a second heater and a protective resistor in series by a relay to connect a first heater and the second heater in parallel if a supplied voltage is low, and connecting the first, second heaters in series if the supplied voltage is high. CONSTITUTION:If an AC power source voltage is low, it is a conducting voltage or less of a constant-voltage element 5 of a detector 3. Accordingly, since a conducting element is not conducted and an SCR 6 is interrupted, 100V is applied to a series circuit of a first heater 1, a second heater 2 and a protective resistor 15. If the AC power source voltage is high, the element 5 is conducted simultaneously when it is supplied, the conducting element 8 is conducted to conduct the SCR 6 to connect the heaters 1, 2 in series, thereby lighting a display 9. |
