To enable the change of a proportional integral and derivative(PID) constant in simple configuration without making the operation of a control system unstable.
First and second MOS FETs 26 and 27 are connected in parallel to a first resistor 21 for a PID constant of a PID control circuit 8 and in a prescribed case, a pulse signal to gradually shorten its repetition cycle is outputted from a CPU 5. Then the first and second MOS FETs 26 and 27 are turned on/off through a first transistor 25 and finally turned into the ON state. Therefore, the first resistor 21 for the PID constant is equivalently and gradually made from a non-short-circuitting state to a short circuit state and the so-called PID constant is equivalently and continuously changed so that the unstable state of control operation is not brought.
HOSHINO KAZUHIKO
SUDO MASAHIRO
FUJIMORI TAKUO
