| 摘要 |
PURPOSE:To minimize influence upon a working current flowing through a circuit including a coil and a voltage applied to the coil by monitoring only counter electromotive force and generating a fault signal. CONSTITUTION:When a transistor (TR)Q1 is turned on by an energizing current, a primary coil 2a is energized. Once the energizing signal is ceased, the TR Q1 is turned off to generate counter electromotive force across the primary coil 2a. The Zener voltage of a Zener diode ZD1 is higher than a battery voltage VB and much lower than the voltage by the cunter electromotive force, so once the counter electromotive force is generated, the current flows through the ZD1, whose anode voltage is divided by resistances R1 and R2 through a diode D1. This divided voltage is compared with a prescribed voltage Va by a comparing circuit 3. When the energizing signal is ceased, the circuit 3 operates to generate a low-level output when the divided voltage is higher than the voltage Va, or a high-level output when latter is low. This high-level output is regarded as a fault signal to turn on a display 4. |
