| 摘要 |
An AC input-free power source comprising a power transformer for receiving an AC input, a rectifier connected to said power transformer for converting the AC input into a DC output, and a switching transistor so driven as to produce a stable current by the switching action thereof. A primary voltage detection circuit is provided with the switching transistor used as a first switching transistor, wherein the voltage to be applied thereto is obtained substantially from the center of the secondary winding of the power transformer, while the AC input voltage is detected and a control signal is outputted in accordance with the value of the detected voltage. A switching input voltage changeover circuit has a second switching transistor and, in response to the control signal, changes the first and second switching transistors selectively for execution of switching action. |
