Why is the inverter switch not easy to start vibration?
The inverter switch is not easy to start vibration. Once it is started, it works normally, indicating that the switching power supply has a sub-health state. Check (B-Ultrasound, CT examination)
Most instruments can't be a problem, only a small number of instruments can be suspected, and replacement is not necessarily possible. Therefore, how to solve the vibration failure that the inverter switch is not easy to start?
1. The probability of 'three forces' design from the source of lead in sub-health state is higher. What is three tops? (1)The starting resistance is too large.
Under 530v DC power supply, the resistance value is generally 300k ~ Between 750 k, I . e. power supply satisfying about 1ma starting current;
In fact, doubts are at 600k ~ The range of 1m is too large. (2)Oscillating power supply chip resistance is too large (Expression may be inaccurate).
Typically powered by rectifier filters is supplied directly, but some models, rectified series resistors (The resistance value is generally 50? 100 Ω)
As for which is the best, it is to increase the filter time constant of the filter to be enhanced by the difference of the effect, it is obvious that the power is more difficult to start a business.
When the inverter can no longer withstand vibration, we can operate according to the following methods: first, the chip is provided to the first 50 connected in series? 100 Ω resistance later said short rectifier. Usually, it's ridiculous!
In the second step, the gate resistance is also effective in parallel.
The third step is to reduce the starting resistance to less than 500 K and change the three power supplies to three normal power supplies, not to mention how high the maintenance rate is, which is basically achieved.
2, supply 7-pin power chip problem, power filter capacitor is the most tired. It provides the excitation energy of the switch tube.
Charge and discharge number 100,000 times per second, charge and discharge current is not small. This is most likely to produce high frequency fatigue (Internal resistance often exceeds 1Ω using SER meter). It is necessary to change the time change.
Due to the high frequency failure of the capacitor, it is difficult to vibrate, accounting for more than 30% of the total failure rate.
In normal operation, when the power supply of 3844B pin 7 is about 12 V, the switch tube is on the under-excitation edge, and the power supply will soon have snoring and vibration failure, which means that the filter capacitor is too tired, unable to maintain.
3. Heavy load and heavy load are not necessarily the failure of the load circuit. Such as: short circuit fault, due to overcurrent.
In the load power circuit, good diode rectifier filter capacitor to help complete the supply task, bad capacitor, become too heavy power load, before it injects liquid, drum, burst top, it's hard to detect.
Instead of checking this part of the capacitor, this problem can be solved.
4, the problem of the chip itself, fundamentally, this is no problem, and it is difficult to expose the chip problem after the vibration begins. But the oscillating chip will also age.
The aging of the switch tube is not a big problem. As long as the excitation pulse is strong enough, the passive switch is also very good.
When the chip is aging and the excitation pulse is weak, the success of the power supply will be greatly reduced.
There is no problem checking other aspects. At this time, changing the chip is a good way to change the chip (Usually I don't like it the most).
5. Short-circuit switch between transformer turns, short-circuit power supply of transformer coil cannot start vibration, and fault can also be judged.
However, there is currently no good method for detecting short-circuit faults between turns.
When the short circuit fault is slight, the power supply can hardly start.
If the load is excluded, the coil measures the output AC voltage amplitude online (
If compared with other coils, such as 5V and 15V coils, the latter should be three times the former)Obviously low. This is the problem of Transformers.