⑴ The input circuit of 220V AC voltage and rectification filtering circuit does not provide sufficient working voltage for the switching tube, exceeding the control range of the pulse width modulation circuit. ⑵ The load circuit has an overcurrent issue, causing the load on the switching power supply to increase and resulting in a decrease in output voltage. ⑶ The on/off interface circuit is in a standby state, causing the switching power supply to operate in a low-frequency oscillation state with output voltage at the standby level. Such a fault should only occur in models where there is no backup power, and the working voltage for the CPU in standby mode is provided by the switching power supply. ⑷ Due to a fault, the on/off interface circuit operates between the on and standby states, causing the switching power supply to work at a frequency between the standby and on states, resulting in output voltage higher than the standby level but lower than the on level. ⑸ The protection circuit is malfunctioning and operating in a conductive state, causing the power supply to enter a weak oscillation and narrow pulse supply mode, leading to a decrease in the output voltage of the switching power supply. ⑹ The diode and filter capacitor in the rectification output circuit, as well as the damaged current-limiting resistor, cause the output voltage to drop. ⑺ The pulse width modulation circuit has an issue and cannot respond tangentially to changes in the output voltage of the switching power supply. The adjustment of the base voltage of the power switch tube is incorrect in direction and magnitude, resulting in a low output voltage of the switching power supply. ⑻ The positive feedback resistance in the positive feedback circuit has increased, the performance of the discharge diode has deteriorated, the positive feedback is insufficient, causing the oscillation period to become longer. The oscillation frequency decreases, thereby causing the output voltage of the switching power supply to be low. ⑼ The flyback switching power supply operates below the low-frequency state due to not receiving reverse conversion, resulting in a low output voltage. Aviation ground power 2, 36V aviation power 1, 400Hz variable frequency power supply 7, 115/200V power supply 2, 27V DC power supply 5, 400Hz power supply 12, aviation power supply.
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