Switching power supplies are reluctant to oscillate
Meet the "power supply" is reluctant to vibrate work, I do the first step is to rectify the chip power supply in series with a 50 ~ 100Ω resistor shorted before. Often work Effective! The second step, the gate resistor in parallel with the 100Ω resistor, also effective ah. The third step, reduce the start-up resistance to 500k or less, change the three power supply for three normal power supply. Repair rate, not to mention how high it is, basically done.
Some people ask: Why is this so designed? Why not before this kind of failure? Repair will occur after this kind of failure? I am three do not know. Barely back Answer: The designer did this, is afraid that we do maintenance of no food. Take care of us.
Against the formation of the three power supply is not easy to vibration failure, replacement really can not solve the problem, simply do a micro-surgery to improve microcirculation, completely solve the problem. Repair Sometimes can not just stay in the "according to the original replacement" on the move where you can change the style.
Two or power supply chip 7 feet of the problem. Power supply filter capacitor is one of the most tired of the main child, to provide switching tube excitation energy, per second kind of charging, discharging tens of thousands of times, and Charge and discharge current is not small, the most likely to produce high-frequency fatigue ah (measured with the SER table internal resistance is often greater than 1 Ω), have to shift in time to replace ah. By the capacitor high-frequency failure Effect caused by the high-frequency failure of the capacitor is not easy to vibrate, at least 30% of the failure rate. Normal operation, measured 3844B 7 feet of power supply if 12V or so, indicating that the switching tube has been in the edge of under-excitation, the power supply will soon appear. Under-excitation edge, the power supply will soon appear hiccups and not easy to vibrate the fault, which shows that the key players - a filter capacitor has been too tired, can not hold out ah.
Third, the load is too heavy. Overload is not necessarily a fault in the load circuit, such as short-circuit failure caused by overcurrent. Load supply circuit, a good filter capacitor can help Help rectifier diode to complete the supply task, and the bad capacitor, it becomes the power supply overload, in its spray liquid, drum top, blowing up before, is very difficult to be noticed. Check and replace this part of the capacitor, may solve the problem.
Fourth, the chip itself. All no problem, start vibration work after the chip's problems are difficult to expose. But the oscillation chip will also be good aging ah. Switching tube aging A little bit of switching tube is really not a big problem, as long as the excitation pulse is strong enough, passive switching is also on the line. When the chip is old, the excitation pulse is weak, and the success of the power supply vibration The success of power supply startup will fall greatly.
Check other aspects of no problem, it is waiting to change the chip is not a good way ah (in general I am the most displeased with the change of a gas).
Fifth, the switching transformer turn-to-turn short circuit. Transformer coil short-circuit power supply can not be vibration, fault or judgement. But the turn-to-turn short-circuit failure, it seems that there has been no good way to Method of measurement. When the short-circuit fault is slight, the power supply can barely start vibration. (A supply voltage is low.) If you exclude the cause of the load, measure the coil output online. AC voltage amplitude (such as other coil comparison, such as 5V and 15V coil comparison, the latter amplitude should be three times the former), is obviously low. That is the transformer problem.
