PURPOSE: To reduce power consumption to effectively protect a semiconductor element, by providing a current detecting means for detecting discharge current, an abnormal discriminating means for discriminating a failure in a DC-DC converter and an oscillation stopping means for stopping the oscillation of the converter.
CONSTITUTION: A DC-DC converter 9 is connected in series to the secondary side of an ignition coil. By energizing an oscillation circuit 14 and a power transistor 13, a high voltage is generated through a secondary winding 12 and is fed to an ignition coil 2. A resistor 20 is disposed as an electrical discharge current detecting means. An abnormal discriminating means 22 through 25 discriminates such that the output of a DC-DC converter 9 is not superposed to discharge current even though the DC-DC converter 9 is in its oscillating condition. An oscillation stopping means 2 stops the oscillation of the DC-DC converter 9 in accordance the result of discrimination. With this arrangement, the power consumption may be reduced and as well a semiconductor is effectively protected.
SATO HIROSHI
YOSHINARI TAKASHI
HITACHI LTD