| 摘要 |
PURPOSE:To set and hold a bias current flowing a magnetic head to an optimum value by detecting the bias current flowing to a magnetic head, comparing an output voltage obtained by rectifying a detection signal with a reference voltage and controlling the oscillating level of a bias oscillator. CONSTITUTION:A voltage VB generated across a resistor 5 and proportional to the bias currnet iB is amplified by an amplifier 10 and rectified by a rectifier circuit 11, then fed to an input terminal of a control circuit 12. A difference between the voltage level of the signal fed to the circuit 12 and a level Vref of a preset reference voltage source 13 is detected and a control signal to eliminate the voltage level difference is fed to the bias oscillator. Then the output signal level of the oscillator 1 is adjusted by the control signal and the current iB is set to an optimum value designated by the voltage source 13. Thus, the bias current fed to the magnetic head 4 is set and held to the optimum value. |
