| 摘要 |
PURPOSE:To prevent destruction of a voltage control amplifier or while of a bias controlling device in the bias controlling device in which output of the voltage control amplifier is applied superposing on recording signals to a recording head by connecting a limiter to the voltage control amplifier. CONSTITUTION:In a normal state, current that flows in the recording head 1 is detected by a low-pass filter 4, and the quantity of effective bias is detected by a peak detector 5. The quantity of effective bias is compared with voltage of a reference voltage source 9 by a comparator 6, and output of the comparator 6 controls gain of the voltage control amplifier 10 to keep the quantity of effective bias constant. Output of the voltage control amplifier 10 is superposed on signal current applied from a signal input terminal 13 by an adder 14 and applied to the recording head 1. In the case where gain control of the voltage control amplifier 10 becomes impossible due to, for instance, the grounding of the inputting section of the peak detector 5, the generation of excessive output of the voltage control amplifier 10 is prevented by the limiter 17. |
