Abstract: An inexpensive flame detector capable of self checking for internal faults, and comprising a detecting photodiode used for detection of a flame, a checking photodiode used for checking function a light source optically coupled to the checking photodiode, an operational amplifier having a feedback resistor connected between the output terminal and non-inverting input terminal thereof, and a decision circuit for receiving the output signal from the amplifier. The checking photodiode is optically isolated from the detecting photodiode and is connected in series, in one embodiment, and in parallel, in another embodiment, with the detecting photodiode. The light source is switched ON and OFF at regular time intervals. The detecting photodiode is connected to the non-inverting input thermal of the operational amplifier. Alternatively, both photodiodes are connected to the non-inverting input terminal.

Abstract: In a capacitive discharge type ignition apparatus, in which an ignition transformer is used, the impedance of the secondary winding of the ignition transformer is comparatively large. This means the power loss is large and the efficiency, in applying a high power voltage to an igniter plug, is lowered. In this invention, a low impedance bypass circuit is connected in parallel circuit with the secondary winding of the ignition transformer, so that the spark current flows through the bypass circuit. By this arrangement, the power loss in the secondary winding is made to be substantially zero. Thus, a powerful spark is generated in the igniter plug efficiently, reliably and with simple circuitry.