| 摘要 |
PURPOSE:To put a writing means into a non-operating state and to enable sure prevention of the breakdown of data by detecting the drop of a power source and turning off transistors regardless of a write enable signal when the power source is interrupted or drops abnormally. CONSTITUTION:A transistor Q11 turns on and Q1 attains zero potential while the power source +V1 is normal. The output terminal of a buffer circuit 10' turns open and current flows to Q1 to generate a voltage between both terminals of a Zener diode D1 when the write enable signal attains L. Q2 of the writing means 20' acts therefore as a constant current source and the output signal from an FF21 inverts at every introduction of write data to said means and is supplied alternately to the bases of Q3, Q4 thus conducting electricity to a magnetic head 22. On the other hand, Q11 turns off and the base potential of Q1 attains +V1 when the voltage of the power source +V1 drops from the Zener voltage V2 of D11 in the case of interruption or abnormal drop of the power source. Q1 is therefore turned off regardless of the output from the circuit 10'. No voltage is thus generated between both terminals of D1 and Q2 turns off. Q3, Q4 are made non-operating. |
