Laptop power adapter without voltage output(手提电脑电源适配器没有电压输出)
Laptop power adapter without voltage output(手提电脑电源适
配器没有电压输出)
Laptop power adapter with no voltage output added to the collector
The brand maintenance process: open the shell to check, find the fuse burned black, that the power circuit short circuit phenomenon. The leakage resistance of the field effect switch tube is measured by a multimeter. The resistance is close to zero. The Q2 is measured by the end effect switch tube. It is found that the drain source has been burned through. When we check the switch power circuit, when the check switch has been damaged, we can not believe that the replacement of the switch after the failure has been ruled out, because there may be a switch drive circuit failure caused damage to the switch tube. If the fault is caused by the drive, then the switch pipe may be burned again after the switch pipe is replaced, resulting in higher maintenance costs. Therefore, we should further check whether the drive circuit is working properly. The circuit uses a flyback drive circuit, and uses a TDA4605-3 integrated circuit to achieve the pulse width modulation control function. Because there is no data on the hand, the circuit is printed according to the printed circuit, such as ^05030801a^. Analysis of the circuit diagram to determine the IC1 power input pin is sixth feet, after power measurement of 6 foot voltage of about 10 volts, indicating that the high voltage rectifier filter circuit is normal, the Q1 and integrated circuit of the starting power circuit is normal. Measure the output pin of fifth pin driving pulse with oscillograph, without waveform output, it is concluded that the integrated circuit is damaged. Ran a few
electronic components shop, only to buy a piece of TDA4605, did not buy 2SK1081 FET, had to buy a more powerful 2SK1082 instead of buying a 3.15A delay fuse. After switching on the component, the energization test shows that there is no 18V voltage output and no burned element, which indicates that the short-circuit fault has been eliminated, but no driving pulse is added to the gate of the mosfet. For further analysis, the 300V DC output of the high-voltage rectifier is added to the second, third pin of the integrated block through R5, C5 and R4, R6 and RT1, respectively, and they are estimated to be field effect tube overheating sampling voltage and city voltage undervoltage sampling voltage respectively. Measuring 3 feet with multimeter, sampling voltage, 2 feet without sampling voltage, removing R5, measuring resistance is infinite, has been broken. Switch on a 1W270K resistor before energizing the test. The power supply has an output voltage, but it drops to zero after one second. The check circuit has not found any other faults, and then the energization test is still only one second voltage output. The power circuit has an output voltage of one second, indicating that the power conversion circuit has begun to work, but it can not continue. Know IC1 in electricity from the early high voltage rectifier 300V obtained by Q1 from the power supply start circuit diagram, circuit work should be replaced by the D4 of T1 winding induction pulse rectifier DC power supply work, now IC1 can not continue to output a drive pulse, may be in the early start IC1 output pulse width is too narrow, the voltage is too low D4 after rectification, can not maintain the control circuit and the circuit work. According to the normal conditions of use should be only one point of failure of the original rules, fault analysis, fault reasons first should be R5, in the R5 damage of the moment, the IC1 pulse drive abnormal,
cause FET burned, so the original TDA4605-3 should be good, then buy IC models for TDA4605, less behind the "-3" parameter may be different, the whole circuit can not maintain the work. After replacing the original TDA4605-3, the power adapter works properly.
The brand experience: in the repair process, due to a lack of care made a few detours. First, check out the IC1 in no pulse output, no peripheral circuit of the integrated circuit further checks, immediately concluded that integrated circuit is damaged; secondly in the purchase of components, without considering the component suffix number different possible differences, so that the maintenance process increased, fault phenomenon increased, prolonged maintenance.