| 摘要 |
PURPOSE:To remove mutual interference between two voltage dividing circuits for setting up two reference level respectively by connecting a circulation preventing diode and two semiconductor switches. CONSTITUTION:At the L level of control voltage CS, transistors (TR)32, 24 are turned off successively. Therefore, the divided voltage of the 1st voltage dividing circuit consisting of resistors 21, 22 is inputted to the reference level input terminal of an error amplifier 20. Since diodes 27, 28 are acted as interference interrupting members even if the resistance values of the resistors 21, 22 are changed, the 1st and 2nd voltage dividing circuits are prevented from mutual interference. When the control voltage CS is turned to the H level and the TR32 is turned on, the resistor 22 of the 1st voltage dividing circuit is short-circuited by the diode 32 and the TR24 is turned on. Consequently, a constant voltage is applied to the 2nd voltage dividing circuit and the divided voltage is impressed to the amplifier 20. In this case also, both the voltage dividing circuits are prevented from mutual interference. |
