| 摘要 |
PURPOSE:To attain an accurate current detection by fixing a potential of a positive side terminal on an operational amplifier by the voltage of zener diode and the differentially amplifying voltage drop of a current detecting resistor. CONSTITUTION:Both ends of the current detecting resistor 10 are connected to both input terminals of the operational amplifier 11 through resistors, and also a resistor 17 and a zener diode 18 are connected in series to both ends of the output terminal on a power supply making a base driving circuit 6 to be operated. Also, the positive side terminal of the diode 18 is connected to the positive side terminal of operational amplifier 11 through a resistor, and a constitution is made so that the voltage proportional to a current is obtained between the output terminal of operational amplifier 11 and the positive side terminal of diode 18. That is, the positive side terminal of operational amplifier 11 amplifying the voltage drop of resistor 10 is fixed by the diode 18, and the values of a feedback resistor 13 and an earth resistor 16 are adjusted to make the operational amplifier 11 to operate as a differential amplifier; therefore, the potential of the positive side terminal of operational amplifier 11 is unchanged with the current of a transistor 5 in output stage, and the current can be accurately detected. |
