No output, the safety tube is normal This phenomenon indicates that the
switching power supply does not work or enters the maintenance state. First
measure the power control chip, a pin voltage, the voltage may start to
be too low voltage, start the external components to leak resistance
and a foot, at this moment if the power control chip is normal, check
the problem through agility. If
there is a startup voltage, the output of the measurement control chip
is a high-level transition or a low-level transition at the start-up
there is no jump, it means that if there is a problem with the control
chip, there is a problem with the peripheral oscillator circuit
component or the maintenance circuit, the control chip can be replaced
first, and then the peripheral components are checked; if there is a
jump, the switch tube is usually faulty.
2. Safe burning or explosion Mainly check the large filter capacitors, rectifier bridge diodes and switching tubes on the 300V. Anti-interference circuit problems will also lead to safe burning and blackening. It should be noted that the current detecting resistor and the power control chip are burnt due to the failure of the switching tube. The negative temperature coefficient thermistor is a simple and safe combustion.
3. There is an output voltage, but the output voltage is too high. This defect usually comes from the regulated sampling and voltage regulation control circuit. In a DC output, sampling resistor, error sampling amplifier such as TL 431, optocoupler, power control chip and other circuits, constitute a closed-loop control loop, any problem will lead to an increase in output voltage.
A low output voltage can result in a low output voltage, which can result in a low output voltage in addition to the voltage control circuitry and for some reason.
The load short-circuit fault of the switching power supply (especially the short circuit or poor function of the DC/DC converter), at this time, should be disconnected from all the load of the switching power supply circuit, so as to distinguish the switching power supply circuit from the load circuit failure. Letter telegram. If the voltage output of the disconnected load circuit is normal, it indicates that it is overloaded; or it still does not normally indicate that the switching power supply circuit is defective.