PURPOSE: To set the threshold voltage accurately in an ignition device which changes the operation level of a power transistor in accordance with the voltage of an electric source by also coperating the operation level of a reference-voltage generating part in accordance with the voltage.
CONSTITUTION: The output voltage V of an AC signal generator 4 is increased in accordance with the increase of the number of revolutions of an engine. The threshold voltage VTH to switch on an input transistor Q2 is also increased. The higher the voltage is, the more the on-time is shortened. On the other hand, the threshold voltage to switch off is almost independent of the electric source voltage. When the operation level of a reference-voltage generating part 6 is operated to be higher, the operation level of an input circuit 5 is lowered. This construction permits to obtain the high allowance of the operation of the threshold voltage characteristic and set the threshold voltage accurately on the side of low electric source voltage, since the reference-voltage generating part 6 is provided symmetrically in parallel with the input circuit 5 for operating in accordance with the electric source voltage.
TANAKA TOSHIO
TOKYO SANYO ELECTRIC CO
NIPPON DENSO CO