| 摘要 |
PROBLEM TO BE SOLVED: To correctly measure a magnetic flux density by controlling a driving current to a Hall element in accordance with a comparative output of a voltage at both ends of a resistor on a current feed path to the Hall element and an output of a voltage circuit driven by the voltage. SOLUTION: A current from a main power source VSS passes through a voltage-input voltage-output type power amplifier TR and an output current detect resistor R and is returned as a current i0 to the main power source VSS via a Hall element RL. A part i2 of the current passes from an A point through a Zener diode current set resistor R3 and a Zener diode ZD and is returned to the main power source VSS via an operational amplifier IC1 for a reference voltage circuit. A comparison circuit is formed of comparison circuit form resistors R1 and R2, the power amplifier TR is an FET satisfying VGS=0V and a voltage gain of g=1, whereby a relationship formula is held. Actual values are, for example, R1=R2=5 kΩ, an internal resistance of the Zener diodeθ=100Ω, R3=6.4 kΩand RS=32Ω. Therefore, supposing thatε=iZ/i0=0.1 and a differential gain A/g of an operational amplifier IC2 for error amplification is set large, i0≈2VZ/63 is obtained by solving the relationship formula. The current i0 running in the Hall element RL is hence constant.
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