Switching power supply is the energy conversion circuit of high frequency switch type, is often used as a power supply equipment, common transformation classification: AC-DC power supply, DC-DC power supply etc.. Switching power supply is the use of modern technology, control transistors switch on and off time ratio, maintain a stable output voltage power supplies.
Switching power supply from the general pulse width modulation (PWM) control IC and MOSFET form. The working process of switching power supply is easy to understand, in the linear power supply, let the power transistors work in a linear mode, unlike linear power supply, PWM power transistor switching power supply is to work during the turn-on and turn off state, in the two states, plus the power transistor on the V-I product is very small, the loss generated power device of the voltammetric product is on the power semiconductor devices. Compared with the linear electric, PWM switching power supply more effective work process is through the input DC voltage through voltage pulse amplitude is equal to the input voltage value to achieve. The duty ratio of the pulse switch power supply by the controller to adjust.
Through the two winding number increase the transformer can increase the output voltage value.
Finally, the AC waveform after rectifying and filtering to obtain the output DC voltage. The main purpose of the controller is to maintain a stable output voltage, the controller and its working process and linear form of the very similar. That is to say the function of the controller block, reference voltage and the error amplifier, can be designed into a device with the same linear regulator.
Switching power supply has two main works: forward converter and boost converter. Although each of them part of the layout of small differences, but the work process vary greatly, in specific applications under each have advantages.
Method for fault detection
Have a basic understanding of switch power supply, we come to have a look the detection andrepair method of fault.
Should first observe the power supply insurance tube is damaged. If the insurance tube damage,not anxious to replace, must first check whether there is the phenomenon of short circuit power supply. Methods: using multimeter resistance gear AC test power insurance after pipe end (test point), the normal resistance should be in tens of ohms or more, such as the resistance is zero,then illustrate the power of existing AC short circuit phenomenon. In addition, we should also focus on examination of the power of the AC filter capacitor is damaged; and if a varistor words, alsoshould check the resistance.
If the above test results normal, then we should be four rectifier diode detection power supply (two test points). In the normal condition, the forward resistance diode as number k (block table test * 1Kwith million), reverse resistance approaches infinity. Such as the discovery of abnormal test results,you need to replace the. Along the investigation down, then have to do is the DC resistance testpower supply part (three test points), the normal resistance is in the number of K, such as the resistance is zero, then shows that there exists a DC short circuit. The cause of DC circuit more, likefilter capacitor short circuit damage, power oscillation tube damage, oscillation integrated block and a peripheral circuit part damage may be caused by short circuit phenomenon. Here, there is a need to explain before replacing the power oscillation tube, must determine the oscillation integrated blocks and peripheral circuit is normal, otherwise it will cause the power tube damage again.
Exclusion of switching power supply after the above issues, explain the fault most samplingfeedback circuit or load in the oscillation circuit. Then, we should first check the power supply circuit oscillation integrated block is normal (four test points), the normal voltage should be around 10V(special reminder: due to the test voltage shall be carried out, in the case of electricity and power supply board has the city electricity, high pressure and therefore pay special attention to personal safety, do not try any part of the direct touch power supply).
If it has no voltage or low voltage dropping resistor, we should first check whether the power supply circuit damaged; secondly to check the oscillation integrated block and its outside is normal. Such as peripheral circuit found no fault, the proposed replacement oscillation integrated block. Of course, sometimes the power supply can not be normal output voltage may also be due to powerload short circuit protection caused by. On the power supply, we only need to be output lineextraction, check that the output voltage is normal (five test points), you can determine the fault position. Rule out the front of the fault, finally also should check the feedback circuit part, generally this part of the fault is mainly concentrated in the photoelectric coupler and its amplification circuit,special attention should be paid to.