| 摘要 |
PURPOSE:To protect against the heating of a power supply and other parts when any fault occurs by providing a means to charge/discharge a condenser and a means to stop the feeding of an output current from a power supply by a voltage at both ends of a condenser. CONSTITUTION:While a normal printing operation is carried out, a prearranged current is supplied to a thermal printing head 2 without the turning ON of a transistor Q2 regardless of a required degree of current for printing. When a voltage V3 has dropped below -Vs continuously due to an accident, the output voltage V5 of a comparator 3 reduces to a zero level and a transistor Q1 is turned OFF. Then a condenser C is charged resulting in the increase of a voltage V6 to (Vz+VBE) after the elapse of a prearranged time. Consequently, the transistor Q2 is switched ON and the voltage V1 of a power supply 1 is set at zero level. The voltage V1 of the power supply 1 continuous to be cut off unless the power supply is reset as a function. Therefore, an output current reaches a zero level after a prearranged time thus eliminating risks such as power supply breakdown or abnormal temperature rise. |
