How to diagnose and handle inverter switching power supply failures
Damage to the switching power supply is the most common fault in many frequency converters, usually caused by the switching power supply. When there is no display, no voltage at the control terminals, or DC12V or DC24V fans not turning, the first consideration should be whether the switching power supply is damaged. An obvious characteristic of a damaged switch power supply is that the frequency converter does not display when powered on. For example, the Fuji G5S frequency converter adopts a two-stage switching power supply, which works by reducing the DC voltage of the main DC circuit from above 500V to around 300V, and then outputting multiple power supplies of 5V and 24V through a first stage switching voltage reduction. Common damages to switch mode power supplies include breakdown of switch tubes, burning out of pulse transformers, damage to secondary output rectifier diodes, prolonged use of filtering capacitors, resulting in changes in capacitor characteristics (reduced capacity or large leakage current), decreased voltage regulation ability, and can also easily cause damage to switch mode power supplies. For example, the switching power supply of the MF series frequency converter adopts the 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 the damage of the switch power supply are as follows:
(1) The environment is polluted, and insulation damage is caused by dust, moisture, and other factors. When the switch power supply has caused deep yellowing and carbonization of the printed board or damage to the printed lines 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 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 switch frequency, withstand voltage, and size of the component can be installed, and maintain insulation distance from surrounding components.
(2) The lifespan of electronic components, especially switch tubes or switch integrated circuits, is more susceptible to damage due to the high current and voltage burden.
(3) The enameled wire of the switch transformer has yellowed, burnt, broken wires between the transformer windings, especially the high-voltage winding, deformed skeleton, and arc jumping marks after long-term use at high temperatures. The transformer wires have been broken over time due to oxidation and corrosion caused by soldering flux.
(4) The switching power transformer itself has a large 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 absorbing components (resistive capacitive elements, voltage regulators, and instantaneous voltage suppression diodes), severe overload occurs, and over time, the absorbed components will be damaged.
