| 摘要 |
PURPOSE:To prevent the overcurrent of a lamp load and to start the lamp load softly, by detecting the overcurrent of the lamp load and providing a circuit consisting of a thyristor by-passing the input current of a transistor (TR). CONSTITUTION:An AC power supply 1 is applied to a potential detecting circuit 3 throuch a diode bridge 2 and the potential voltage-divided by the circuit 3 is applied to the thyristor 14 to detect prescribed potential in a half-wave and control the TR 15 in a control circuit 4. By controlling the TR 15, voltage having an always constant control period is applied to the lamp load 5. In addition, a TR 6 connected to the load 5 in series, resistors 21, 22 and the thyristor 24 are connected to the output side of the TR 15. The overcurrent of the load 5 is detected by the voltage applied to both the ends of the resistor 21, and when the voltage reaches prescribed voltage, the thyristor 24 is turned on and input current of the TR 15 to the load 5 is by-passed, so that the load 5 is prevented from overcurrent and solft starting is made possible. |
