| 摘要 |
PURPOSE:To make possible to employ a relay having small contact capacity by arranging a parallel circuit of a relay contact and a resistor at a power supply input section, connecting a relay coil and a transistor to the power supply input section, and turning the relay coil ON through a transistor. CONSTITUTION:A relay contact 1a is connected in parallel with a resistor R1 and interposed between a power supply input section and a power supply output section. A relay coil 1b is driven by a drive transistor Q1. Base of the transistor Q1 is connected with a constant voltage circuit comprising a Zener diode ZD and a resistor R2. In case of heavy load due to some cause, the relay coil drive transistor is turned OFF thus interrupting the relay coil driving current. If the heavy load state endures even if the applying voltage of power source switching circuit has a rated value, the relay coil driving transistor Q1 is turned OFF thus preventing pumping of relay contact. |
