Three common faults and maintenance methods for inverter switching power supply circuits

　　Author ：Iflowpower – Portable Power Station Supplier

The switching power supply circuit of the inverter can be simplified as the above circuit model, and the key elements in the circuit are contained. And any complicated switching power supply, after removing the branches, there will be the backbone of the above picture. It is indeed the ability to "simplify" the "simplification" of complex circuits, and it is necessary to stretch in circuits that seem to be chaotic.

To learn from the bull's dumin, train your own insights, there is no overall switching power supply circuit, only part of the context and the trend of the context - oscillation loop, regulator loop, protective loop and load circuit, etc. Look at the cases in the circuit. 1.

Oscillation loop: The main winding N1, Q1 of the switching transformer, the drain-source, R4 is the passage of the power working current; R1 supplies the start current; the power supply winding N2, D1, C1 form the power supply voltage of the oscillation chip. The normal operation of these three links is a prerequisite for power supply. Of course, the 4 foot of the PC1 is connected to the elements R2, C2 and PC1 chips itself, and also constitutes a portion of the oscillation circuit.

2, voltage regulator loop: N3, D3, C4, etc. + 5V power supply, R7-R10, PC3, R5, R6 and other components constitute a regulator control loop. Of course, the PC1 chip and 1, 2 foot peripheral components R3, C3 are also part of the regulator loop.

3 Signal signal, can also be considered as a voltage protection signal. However, the content of the protection circuit is not only limited to the protection circuit itself, and the control of the protection circuit is often caused by the abnormality of the load circuit. 4, load loop: N3, N4 secondary windings and subsequent circuits, all load loops.

The abnormality of the load loop will involve the protection loop and regulatory circuit, so that the two loops make corresponding protection and adjustment actions. The oscillation chip itself participates in and constitutes the top three loops, the chip is damaged, and the three loops will strike together. For three or four circuits, it is carried out under normal chip itself.

In addition, it is necessary to make a fault judgment like a global concept and system ideas, and through the phenomenon. If the changing fault is not caused by damage to the oscillation loop element, it is possible to be a regulator loop fault or load loop abnormality, resulting in control of the internal protection circuit of the chip, and stopping the output of the PWM pulse. It is not possible to completely inspector with each loop, and the emergence of a faulty component is likely to show the effect of "holding a whole and body movement".

Switching power supply circuits often appear as the following three typical faults: First, secondary load supply voltages are 0V. There is no reaction after the inverter is powered on, the operation display panel is not indicated, and the 24V and 10V voltage of the control terminal is 0V. Check the main circuit charging resistance or precharge loop is intact, it can be judged as switching power supply failure.

The maintenance steps are as follows: 1. The circuit is easy to damage the element is a switch tube. When it is damaged, the R4 becomes larger or broken by the impact.

Q1's G polarized resistance, oscillation chip PC1 is often damaged by strong electric shock, and must be replaced at the same time; check the load loop has short-circuit phenomenon, exclude. 2, replace the damaged parts, or have short circuit components in the undetection, can perform power-on check, further judgment is the oscillation circuit or the regulator loop. Inspection method: a, first check the start resistor R1 has a loop.

Once normal, use 18V DC power pen to the 7, 5 feet of UC3844, and power on the oscillation circuit. The measurement of 8 feet should have a 5V voltage output; 6 foot should have a voltage output of around 1V. Note that the oscillation circuit is basically normal, the fault is in the regulator circuit; if the 8 feet have 5V voltage output, 6 foot voltages are 0V, check 8, 4 foot external R, C on time components, 6 foot peripheral circuits; if 8 feet, 6 foot voltages are 0V, UC3844 oscillating chip is broken, replace.

b, the UC3844 is individually powered on, shorted the PC2 input side, and if the circuit is activated, the fault is in the PC2 input side peripheral circuit; the circuit does not control, check the PC2 output side circuit. Second, the switching power supply has intermittent oscillation, can hear "snoring" or "" sound, or hear "snoring" sound, but when the operation display panel is on time. This is a typical fault feature of the power supply overload due to abnormal load circuitry.

The abnormality of the load current increases, causing a large rise in the primary winding exclamation, a voltage signal of 1V or more in the current sampling resistor R4, which causes the UC3844 internal current test circuit to control the circuit stop; the overflow signal is disappeared on the R4, and the circuit is Reproduction, so cycle reciprocation, intermittent oscillation. Inspection method: a, measure the resistance value of the power supply circuit C4, C5, if there is a short-circuited straight-through phenomenon, there may be short circuits in the rectifier diode D3, D4; observe the C4, C5, there is no drum top, spray liquid, etc., if necessary Under the test; the power supply circuit has no abnormality, which may be short-circuit faulty components for the load circuit; B.

Check the power supply circuit has no abnormalities, power-on, use exclusion method, and exclude all the power supply. If the fan power supply terminal is unplugged, the switching power supply is working properly, and the operation display panel is normal display, the 24V heat dissipation fan is damaged; unplug the + 5V power supply, the power supply copper foil, the switching power supply is normal, then + 5V load circuit Damaged components. Third, the power supply voltage of the load circuit is too high or too low.

The oscillation circuit of the switching power supply is normal, the problem is in the regulator loop. The output voltage is too high, the components of the regulator circuit are damaged or inefficient to make the feedback voltage amplitude. Inspection Measures: a, in the PC2 output and 10K resistor, the output voltage falls.

Note that the PC2 output side voltage regulator circuit is normal, the fault is in the PC2 itself and the input side circuit; B, in parallel with 500Ω resistors on the R7, the output voltage has a significant return. Explain that the photocoupler PC2 is good, the fault is PC3 inefficient or PC3 external resistance element variable value. Conversely, for PC2 poor.

The load voltage is too low, there are three faults possible: 1, the load is too heavy, the output voltage is lowered; 2, the voltage regulated loop element is poor, resulting in too much voltage feedback signal; 3, the switch tube is inefficient, so that the circuit (switch transformer) Insufficient exchange. Inspection and repair Measures: a, will be released one by one by one (notice! Do not take off the load circuit in the way to power the traffic tube, especially the + 5V supply circuit of the regulated feedback signal! Feedback The disappearance of the voltage signal can cause an abnormality of each output voltage, and the load circuit is burn!) Judgment is due to the load of the load; if the power is turned off, the circuit rises to normal, indicating the switching power supply. It is normal, check the load circuit; the output voltage is low, check the regulated circuit.

B. Check the resistance element R5-R10 of the regulated circuit, no change value; change the PC2, PC3 one by one, if normal, explain the transform element is inefficient, and the internal resistance is large. c.

Switching the PC2, if the PC3 is invalid, the fault may be inefficient, or there is a problem with the switch and excitation circuit, nor is thereafter eliminated by the internal output circuit of the UC3844. Replace high quality switch tube, UC3844. For general faults, the above troubleshooting method is effective, but not necessarily 100% Light.

If you check the oscillation loop, the regulator loop, the load circuit has no abnormality, the circuit is still low output, or the intermittent oscillation, or simply without reacting, this situation may appear. Don't be guilty, let us go deep into the original cause of the circuit fault to help find the faulty component as soon as possible. The difference between the circuit's intermittent oscillation or stop-enriched is not in the reseudent loop and the regulator circuit.

What is the original can cause the circuit that does not control? (1) R, D, C circuit in parallel two ends of the main winding N1, for spikes Voltage absorbing network, during the pre-supply switch tube break, stored in the discharge path of magnetic field energy in the transformer (the reverse current passage of the switch), protected the switch tube to be broken. When D2 or C4 severely leakage or breaks through a short circuit, the power supply is equivalent to plus a very heavy load, so that the output voltage is severely fallen, the U3844 is insufficient, and the internal undervoltage protection circuit is controlled, and the circuit enters intermittent oscillation. Because the components are connected in parallel in the N1 winding, it is often not easy to measure, and it is often overlooked; (2) Some switching power supplies have (voltage excessive) protection circuits in the input supply voltage, once the circuit itself fault, makes the circuit error protection Action, circuit stop; (3) poor current sampling resistance, such as pin oxidation, carbonization or resistance, result in rising pressure drop, malfunction protection, so that the circuit enters the intermittent oscillation state; (4) self-powered The rectifier diode D1 of the winding is inefficient.

The forward direction is large, the circuit cannot be activated, replaced; (5) switching transformer due to winding mold, moisture, etc. The R1 rocking circuit parameter variation, but the measurement does not exceed the abnormality, or the switch tube is inefficient, and there is no abnormality in the circuit, but it does not. Repair method: Change the circuit with both parameters and states, so that the fault is exposed! Try reduction of the resistance value of R1 (less than less than 200KΩ or less), the circuit can vibrate.

This method can also be one of the emergency repairs. Invalid, replacement switch, UC3844, switch transformer experiment. The output voltage is always high or low, and the normal value is not met.

The inspection does not have an abnormality of the circuit and components, almost replace all components in the circuit, the output voltage value of the circuit is still "barely and make" state, sometimes "normal work", but people are not practical, like neuropia I don't know when I will come to an "abnormal performance". Don't give up, adjust the circuit parameters, so that the output circuit reaches the normal value, reaches its working state, let us "rest assured". The variation of the circuit parameters has the following originals: 1, transistor is inefficient, such as decrease in transistors, or largest the internal resistance, the positive electrical resistance is large, and the reverse resistance becomes small, etc .

; 2, use a multimeter The correlated medium loss, frequency loss, etc. of the measured capacitor; 3, the aging and parameter drift of the transistor, the chip device, such as the light transfer efficiency of the photocoupler, etc., the inductive element, such as the Q value of the switching transformer, etc.

5. The resistance value of the resistance element varies, but does not significant. 6.

These five kinds of originals are all kinds of "integrated use". This state of "present" is a "path", which is a "path", maybe we have to change the maintenance ideas, the Chinese medicine has a "dialective treatment" theory, we have to use it. The next square is not for which component is specified, but the entire circuit "conditioning", making it "pathological" "normal".

It's so "blurred", giving illness. Repair method (slight adjustment of element values): 1, low output voltage: A, increase R5 or reduce R6 resistance value; B, reduce R7, R8 resistance value or increase R9 resistance value. 2, the output voltage is high: a, reduce R5 or increase the R6 resistance value; B, increase R7, R8 resistance value or reduce R9 resistance value.

The purpose of the above adjustment is to completely check the circuit, replace the inefficient component,. The purpose is to adjust the relevant gain of the regulator feedback circuit, making the pulse duty cycle of the oscillation chip output, the energy storage of the switching transformer changes the output voltage of the secondary winding reaches the normal value, the circuit enters a new "normal balance" condition. A lot of difficult problems that seem to be repaired, so that the adjustment of the two resistance values, the waves are uncomfortable.

Issues that should be paid in the maintenance: 1. During the switching power inspection and repair process, the power supply of the three-phase output circuit IGBT module should be cut, and the power supply is abnormal, causing damage to the IGBT module; 2. Excessive repair output voltage is too high.

When the fault is broken, the + 5V is cut off to the power supply of the CPU motherboard, so as not to avoid the CPU, causing the CPU motherboard. 3. Do not interrupt the regulator loop, will result in an exception of the output voltage! Diode.

4, after the switch is damaged, it is best to change from the original model. This is so developed in the network, the source of goods is not a problem, usually can be purchased. Many things on Taobao can purchase cheap prices, pay attention to quality!.