| 摘要 |
PURPOSE:To maintain a load current constant with respect to the variation in the voltage of a power source by rectifying the voltage of a power source, and supplying the rectified voltage to the gate circuit of an FET, thereby regulating the gate voltage. CONSTITUTION:The gate voltage of an FET 10 satisfies the condition of an equation, where I10 represents a current which flows through the FET10, I17 represents a current which flows through a resistor 12 from a transformer 17, R11 represents the resistance value of a variable resistor 11, and R12 represents the resistance value of the resistor 12. Thus, when the voltage of a power source 1 becomes high, the voltage of the transformer 17 rises, the current I17 increases, and the voltage VGS becomes high at the negative side, thereby decreasing the current which flows through the FET10. Accordingly, the charging current to the capacitor 5 decreases, causing a thyristor 3 to be delayed in conducting ON and the conducting angle of the load current of a motor 2 to become narrow. As a consequence, the power consumed at the load does not alter. Conversely, when the voltage decreases, the power can be maintained constant. |
