Analysis of Abnormal Phenomena in Power Supply Design and Commissioning

Some abnormal phenomena seen during debugging and subsequent solutions. In fact, many engineers think that designing power supply is a very experienced technology, which should be well-informed. This experience is not only reflected in the design, but also in the commissioning process.

When you see the waveform, you can locate the problem, which is the highest level. Next, I will post those records a little bit. Of course, I hope netizens can also share those impressive debugging experiences in this post.

Project: UC3842 control circuit learning board

Phenomenon: UC3842 power supply is normal, but VREF is not 5V, but higher than 5V.

Solution: re weld the pins.

Analysis: the GND pin of UC3842 is poorly welded, resulting in voltage floating.

Project: a power supply in a laboratory is broken. Take it apart and have a look. The full bridge controlled by UC3875 needs to be repaired.

Phenomenon: after preliminary inspection, the power tube is broken. Since there is no tube of the same model, replace all tubes with tubes of the same power level. After power on, when the input voltage is low, everything is normal. When the input voltage is high, the drive is chaotic and the frequency jitters.

Solution: increase the driving resistance of the power tube, the phenomenon disappears, everything is normal, and the power supply is repaired.

Analysis: the parasitic parameters of the new tube are different from those of the old tube. Under the same driving circuit, the switching speed will be relatively fast, resulting in large interference. At high voltage, the interference will affect the work of the control circuit.

Project: uc3845 double tube forward

Phenomenon: after the two tubes are turned off, the voltage borne by DS is very different, not half of that in theory. Guess is     The inconsistent parameters of MOS lead to welding down the upper and lower tubes and exchanging positions. The result is the same. It seems that it has nothing to do with MOS.

Solution: adjust the two tube drives to make them turn off at the same time as much as possible. The situation is slightly improved, but the voltage cannot be divided equally.

Analysis: this should be caused by two reasons. One is the difference of PCB parasitic parameters. The actual capacitance of DS of tubes at two positions is different. The other is that the drive is not very synchronous shut-down.

Project: uc3845 control flyback of auxiliary winding feedback

Phenomenon: the output voltage of the main circuit has a great overshoot when starting up. However, the voltage of the auxiliary winding participating in the feedback does not overshoot.

Solution: in order to adjust the adjustment rate, a resistor is connected in series on the auxiliary group winding. When the resistance value of this resistor is reduced, the output overshoot of the main circuit is significantly reduced.

Analysis: because the feedback sampling is the auxiliary group winding, and the auxiliary group winding is connected with a resistance in series, there is a voltage difference between the voltage of the auxiliary group winding and the voltage at the feedback, which is coupled through the transformer, resulting in output voltage overshoot.

Project: NCP1014, optical lotus feedback flyback

Phenomenon: after a mature board that has been made by others is re welded, it is found that the output voltage stabilization is wrong.

Solution: change the 431 of other models with the same benchmark to replace the 431 in the original BOM. Just change it back.

Analysis: Zetex 431 was originally used, and its minimum working current is UA, so the minimum working current is basically not considered in the design. Later, Ti 431 was replaced, and the minimum working current was 1mA, resulting in abnormal operation.

Project: ice1pcs01 control boost   PFC

Phenomenon: in the full voltage range, when regulated by the voltage regulator, the input current waveform is very good, and the high-frequency ripple is very small. Only when the input voltage is about 220V, the high-frequency ripple of the input current suddenly increases. Greater than 220V, and less than 220V are very small

Solution: just use AC souce. The high-frequency ripple under any voltage is relatively large, ha ha.

Analysis: the self coupling voltage regulator is used. The self coupling voltage regulator has leakage inductance. The leakage inductance can filter out the input high-frequency ripple current, but when it reaches 220V (network voltage), the output end of the self coupling voltage regulator is actually directly connected to the input end, so naturally there is no leakage inductance.

Project: uc3845 double tube flyback

Phenomenon: unstable drive, constant jitter, transformer Zizi call. It is useless to adjust the loop. Look at the sawtooth waveform of uc3845 oscillation pin with an oscilloscope and find that the frequency of sawtooth wave is jittery. Uc3845 has a fixed frequency. It seems that there is interference.

Solution: strictly separate the ground and power of the control circuit, and then connect it at a single point. The driving signal is stable, the frequency is fixed, and the transformer stops barking. But damn it, the conduction got worse. Perhaps the legendary frequency jitter is indeed good for conduction.

Analysis: layout is very important in power supply design, especially the layout of ground, the separation of power ground and signal ground, and single point grounding. It is to avoid high-frequency power current flowing through the signal ground plane, otherwise it will interfere with the control circuit.

Project: ucc3895 current mode control, phase shift control, full bridge, double current rectifier

Phenomenon: the transformer is biased

Solution: thicken one PCB power line of the secondary power circuit. The PCB wiring is connected to an inductance of the current doubling rectifier circuit. Magnetic bias disappears

Analysis: the current doubling rectifier circuit has a unique problem, that is, the average current on the two inductors will be inconsistent. If current mode control is adopted, the control signal will ensure that the positive and negative current peaks of the primary transformer are the same. If the positive and negative currents of the secondary transformer are inconsistent, magnetic bias will occur.

The average current of the inductors is inconsistent because the DC impedance of the two inductors is different. However, in fact, the inductance of the same batch is not so different. On the contrary, the PCB wiring connecting these inductors is quite different, resulting in a large difference in the actual DC resistance of the two inductors (plus the resistance of PCB wiring).

Project: 431 plus optical coupling feedback flyback

Phenomenon: the regulation rate of output voltage is very poor, and the voltage decreases obviously with the increase of load. The voltage difference between the measuring voltage sampling point and the output pin is not large.

Solution: connect a small capacitor between the reference pin of 431 and the cathode. The adjustment rate immediately improved.

Analysis: the reference foot of 431 is disturbed.

Project: IR1150   boost PFC

Phenomenon: the switching frequency is 100k, but the input has 1kHz ripple current. The X capacitor squeaks.

Solution: adjust EMI filter parameters.

Analysis: EMI filter resonates itself.

Project: flyback synchronous rectifier

Phenomenon: the voltage spike of synchronous rectifier is very high, so it can't be absorbed.

Solution: replace the synchronous tube with a tube with a fast recovery diode

Analysis: the reverse recovery time of the body diode of the synchronous tube is too long, resulting in a large reverse recovery current. This causes severe voltage spikes.

Project: IR1150 PFC

Phenomenon: during high temperature test, the shell temperature of MOSFET is only 80 degrees, so it's fried chicken. In the previous several sets, the shell temperature of MOS reached 110 degrees, all safe and sound.

Solution: find out the cause and find out that the driving resistance was welded incorrectly. It was originally 10R, but it was welded to 100r

Analysis: too large driving resistance leads to large MOS loss. Similarly, due to the junction to shell thermal resistance, large power consumption will lead to large temperature difference. Although the shell temperature is only 80 ℃, the actual junction temperature has exceeded the bearing range of MOS.

Project: L4981 PFC

Phenomenon: when no-load power on, the drive is chaotic, and the oscillation frequency changes significantly. The higher the input voltage, the worse. At first, I thought that if the ground wire was not laid well and the PCB was cut and cut, it could not be solved.

Solution: after carefully examining the PCB, it is found that a power line is close to the control circuit, and the power line is connected to the D pole of MOSFET. It is useless to cut off the power line and let the power current go around the place far away from the control circuit. The PCB copper wire close to the control circuit is made into an island, which becomes dead copper, and the interference disappears.

Analysis: due to electric field interference, the d-pole of MOS is a great place for DV / DT, resulting in great common mode interference. Therefore, the control circuit should be as far away from this point as possible.

Welcome to reprint, this article comes from the electronic enthusiast network( )

recherches chaudes
Tractor Manufacturers in China, Cheap 12HP Farm Hand Walking Tractors Hot Sale Agricultural Field Cultivator for Field Operations rotary cultivator tiller Pellet Machine Multi-Purpose 50HP 55 HP Tractor 4WD Used Compact Farm Tractor for Sale professional truck mounted mist spraying machine high pressure mist fog sprayer for garden1 Aliments pour vaches animales faisant le traitement Machine à granulés de granulateur entièrement automatique Machine d'alimentation domestique 16000 BTU Gas fired Table top heater for outdoor use for home use Hot Selling China Mini Trailer Machine à désherber le moteur à essence RATO 7HP modèle de démarrage manuel et électrique pour vous Option Agricultural Machinery Farm Machine Mini Power Tiller Gt1050d/a 6HP Farm Cultivator and Gasoline Tiller
articles chauds
What Led to Racial Relations Being Better in Namibia and Botswana, Compared to South Africa?
A poultry farmer collects eggs every morning. There are 50 broken eggs per collection on average. What is the probability that more than 60 eggs might be
Is there anyone recovered from covid-19? Can you share your hospital bills?
Farm Machinery in Ethiopia Bolstering the Agricultural Backbone
Chinese Government Assists Dominica with 2,500 Solar Street Light with Battery and Panel
Which would win, a Landkreuser P 1000 Ratte and Maus tank or a Bob Semple tank?
UNICAR Guatemala, the Aortic Valve Replacement Hospital in Guatemala City
Controlling a Stepper Motor with a Siemens S7 1200
Is There a Reason That I Need a HUD App'd Water Heater Or a Special Water Heater for a Mobile Home/t
Theatrical Trailer
sliding gate Articles Liés
Tips to Help You Design the Perfect Solar Battery for That Party
Functional Features and Application Introduction of TG452 Series Intelligent Street Lamp Gateway
What Is the Best the Best Solar Street Light for You? - the Best Solar Street Light Reviews
IGBT of Fuji Motor Electronic Equipment Technology
Is a Metal Roof Right for You | Billy

Copyright © 2020  Shandong Abusair Agricultural Machinery Co,. Ltd- |  Sitemap

Multifunctional farm Abusair machinery  |  Tea Professional Cultivator farm machinery