| 摘要 |
<p>In a switching power supply, a superimposition circuit (2) made up of a resistor member (32) is connected in parallel to the primary coil (3) of a transformer (6). A superimposition current is supplied to a current sensing circuit (9) during the period when a switching element (7) is in the ON state. The current sensing circuit (9) detects the current flowing through the primary coil (3) during the switch-on period. According to the detected current, a switch control circuit (19) controls switching on and off of the switching element (7) so as to stabilize the voltage (Vout) output by the power supply. When the current becomes low, for example in the case where the circuit has a light load or receives a high input voltage, noise would usually have a significant adverse effect. However, since the detected current in the current sensing circuit (9) is biased to become large, by superimposing the superimposition current (i1) of the superimposition circuit (2) on the current (i) flowing through the primary coil (3), the output voltage is stabilized without being adversely affected by noise, even if the current passing through the primary coil becomes low. <IMAGE></p> |
