| 摘要 |
PURPOSE:To make the constant-current duration of an ignition coil constant over a wide range of running of an engine by determining the on timing of the ignition coil such that a predetermined count is obtained by counting of clock pulses during a period of time in which the constant-current condition is held detected. CONSTITUTION:A control unit 4 provides a rectangular wave X for determining an ignition timing in accordance with a rotational frequency representing signal N and a suction air amount representing signal Q. A constant-current control circuit 5 turns a transistor Tr2 conducting by a leading edge of the signal X and controls the current through the transistor Tr2 such that the current flowing through the primary winding of the ignition coil is kept constant. The transistor Tr2 is brought out of conducting by a trailing edge of the signal X so as to cause high voltage to be produced in the secondary winding of the ignition coil 1. A constant-current condition detecting circuit 7 generates rectangular wave signals Z while the current Y flowing through the primary winding is held constant. A counter 6 counts clock pulses C while a signal Z is held high. The control unit 4 determines the energization duration for a sebsequent next ignition cycle in accordance with the output of the counter 6. |
