| 摘要 |
PURPOSE:To eliminate unnecessary power consumption and to increase the efficiency, by increasing a current flowing to a dummy resistor only when the conduction width at switching is decreased. CONSTITUTION:The conduction width of a primary pulse is detected with the 2nd secondary winding W at the secondary side of a transformer T, a rectified voltage is introducted to a rectifying circuit RECIII and a comparison voltage with the voltage division of the output voltage is used for a bias voltage of a transistor (TR)TD connected in series with a dummy resistor DR. When a load current is small, i.e., the conduction width is small, the TRTD is forward- biased and conductive, and a current flowing to the dummy resistor DR is larger, a load current is increased. As the conduction width is increased, the forward bias voltage is smaller, and the TRTD is nonconductive, causing the same state that the dummy resistor DR is eliminated. That is, detects of useless power consumption during the normal operation of the power supply can be avoided. |
