| 摘要 |
PURPOSE:To reduce not only friction load at the time of the spacing operation of a thermal head but also noise generated when a platen is pressed without decreasing a speed, in a circuit of a constant current system for driving a magnet for pressing and opening the platen of a thermal head and a circuit of an open loop chopping system, by allowing an over-drive current to have a differentiation wave form. CONSTITUTION:A differentiation circuit constituted of a condenser C2 and a resistor R10 is added to a conventional circuit and a resistor R9 for keeping a holding current and a diode D are further added thereto. By this circuit, the moment a MAOVDV signal generated the change of 0 1 at time t1 voltage V1 generates the change of V12 V11. As a result, VB lowers by voltage VD and VB4 comes to VB1 by the charging of the condenser C2. The over-drive current i1 of a magnet MG comes to a differentiation wave form and a holding current i2 is kept constant. In an open chopping system, Tr1 repeats ON-OFF by the cycle of 1, 0 of a MGDV signal to control the over-drive signal i1 to form the differentiation wave form. |
