How to diagnose and handle switch power supply faults?
Damaged switching power supply is the most common fault in many frequency converters, usually due to the occurrence of a switching power supply. When there is no display, no voltage at the control terminal, or DC12V or DC24V fans not rotating, the first consideration should be whether the switching power supply is damaged. One obvious feature of switch power supply damage is that there is no display after the inverter is powered on. For example, the Fuji G5S frequency converter adopts a two-stage switching power supply, which is based on the principle that the DC voltage of the main DC circuit is reduced from over 500V to about 300V, and then output a 5V, 24V multi-channel power supply through a one-stage switch voltage reduction. The common damages to switching power supplies include breakdown of switch tubes, burning of pulse transformers, damage to secondary output rectifier diodes, prolonged use of filter capacitors, resulting in changes in capacitor characteristics (reduced capacity or high leakage current), decreased voltage stability, and easy damage to switching power supplies. For example, the switching power supply of the MF series frequency converter adopts a common flyback switching power supply control method. A short circuit in the output stage circuit of the switching power supply can also cause damage to the switching power supply, resulting in no display of the frequency converter. The reasons for damage to the switching power supply are as follows:
(1) Environmental pollution, insulation damage caused by dust, moisture, etc. When the switching power supply has caused deep yellowing and carbonization of the printed board or damage to the printed wire due to local high temperature, and the insulation, copper foil, and wires of the printed board are no longer usable, the printed board can only be replaced as a whole. After identifying the damaged components, replace them with new ones. The component model should be consistent with the prototype number. If it cannot be consistent, confirm whether the power switching frequency, withstand voltage, and size of the components can be installed, and maintain insulation spacing with surrounding components.
(2) The lifespan of the components themselves is a problem, especially for switch tubes or switch integrated circuits, which are more susceptible to damage due to their high current and voltage burden.
(3) The enameled wires of switch transformers have been used at high temperatures for a long time and exhibit yellowing, scorching odor, breakdown between transformer windings, broken wires in transformer windings, especially in high-voltage windings, and deformation and arc jumping marks on the skeleton. The transformer wire has been broken for a long time due to oxidation and flux corrosion.
(4) The switch power transformer itself has a high leakage inductance, and the leakage inductance of the primary winding during operation causes a large amount of energy overvoltage. When this energy is absorbed by the absorbed components (resistance capacitance components, voltage regulator tubes, instantaneous voltage suppression diodes), serious overload occurs, and the absorbed components will be damaged over time.
