| 摘要 |
A switching power supply contains a transformer. Connected on the secondary side of the transformer is a dummy load circuit. The dummy load circuit rectifies, voltage divides and low-pass filters the signal on the secondary side of the transformer. If the output of the low-pass filter is below a predetermined value, it is recognized that an insufficient load (which might be no load at all) is connected to the output of the switching power supply. In that case, the dummy load circuit activates a transistor which switches a dummy load resistor across the output of the power supply to assure at least a predetermined minimum electrical load on the output. If the electrical loads on the output of the switching power supply include a voltage source such as a battery, a relay is connected in series with the dummy load resistor within the switching power supply. The relay opens when the switching power supply is turned off, to prevent inadvertent leakage current from the voltage source through the transistor which switches the dummy load resistor.
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