One: Energy-saving lamps are becoming more and more popular. Because electronic ballast reduces iron consumption and saves energy, it is the development direction of light source. Most of the obstacles of energy-saving lamps are electronic ballasts. This paper introduces the maintenance methods of common faults. Because the line is directly connected to the mains, there is a danger of electric shock. It is best to prepare an isolation transformer for maintenance, which is safe and convenient for power-on inspection. First, the appearance inspection should be carried out, and then the power-on inspection can be carried out. Before electrifying, measure the resistance of point A and point B with multimeter, which should be tens of kiloohms; After electrifying, point A and point B should have 300V DC voltage, and the lamp should be able to emit light; If it doesn't light up, it should be clear that the fault point is in the trigger circuit or the series harmonic starting circuit. Monitor whether there is AC voltage at both ends of the lamp tube with AC 500V block. If there is AC voltage, the circuit has started to vibrate, and the fault point is in the series harmonic starting circuit, which may be the leakage of the starting circuit. If there is no AC voltage, it may be that the starting capacitor is short-circuited or there is no vibration, so the trigger circuit is mainly checked. C2, R 1, d in figure 2; In figure 1, the resistance of R2 and R3 increases or the performance of V2 deteriorates, and the bias current provided is not enough to make V2 enter the self-excited state. As long as the resistance is properly adjusted, V2 will start to vibrate. C2 leakage prevents the bidirectional diode from reaching the turning voltage, and V2 cannot enter the oscillation state. You can try another bidirectional diode. When the electricity in series between the trigger tube and the B pole increases and the β value of the tube is low, it is difficult to start vibration. Requirements for triode: The PCM and ICM of high wattage lamp triode should also be larger, and the ICM should be large enough to make the two triodes work alternately in the saturated on-off state. Generally, 30-40 watt lamps are MJE 13005-7-7 or BUT10/A, and an aluminum radiator is added to avoid overheating damage when the ambient temperature rises in summer. Commonly used high back pressure pipes are 2SC2482, DK52 and DK53. Except 2482, radiator can be installed. If the radiator is connected to the C pole of the lamp tube, there will be high voltage, so pay attention to insulation to prevent short circuit between the poles. Analysis of several typical faults: 1, the lamp can emit light, but it has obvious flicker, and the capacitance of C4 and C5 in figure 1 is reduced; These two electrolytic capacitors not only play the role of power supply filtering, but also participate in oscillation. When the capacitance decreases, the charging and discharging current will also decrease, causing the lamp to flicker. 2. The lamp tube does not emit light only at both ends (sometimes red), mostly because the starting capacitor is broken, and the filament will be damaged after a long time, which is the most sensitive in the double U-shaped lamp. In addition, if the filter capacitance value in Figure 2 drops below 1μF or the starting capacitance value is too small, a rolling aperture (also called spiral light) will appear with flicker. The ballast of 3.30 ~ 40W straight fluorescent lamp is installed at both ends of the lamp tube in two parts. In order to replace the lamp tube conveniently, the filament and the circuit are connected in a detachable and elastic way (different from U-shaped energy-saving lamps). It should be noted that after installing the lamp tube, it is necessary to check whether the filament is reliably connected to the line before turning on the power supply. If the power supply is not on, adjust the lamp tube, which is easy to damage the triode during the adjustment. Because the electronic ballast works under the condition of high frequency oscillation above 20kHz, the filament is a part of the oscillation circuit, and the inductance and capacitance in the circuit are energy storage elements. The filament circuit is intermittently turned on and off, and high-amplitude sharp pulses are bound to appear in the circuit, which is easy to breakdown the triode. It is common to adjust the lamp tube after the inductance ballast fluorescent lamp is energized, while the electronic ballast fluorescent lamp should be turned off first and then adjusted. The welding time of low wattage carbon film resistor should not be too long. Overheating will loosen the lead caps at both ends, increase the resistance and make them unstable. Especially in the series circuit of B-pole of triode, there will be intermittent oscillation or even breakdown of the tube, so it is not easy to check the fault point. It is best to use a metal film resistor of not less than 1/4 watts. China Electronic Ballast Network (lack of drawings)

2. Compared with inductive ballast, electronic ballast for fluorescent lamp is light in weight and easy to hang; Low pressure and easy to start; Luminescence without flicker, the most prominent advantage is energy saving. The electronic ballasts of many products are divided into two parts and placed at both ends of the lamp holder (as shown in the figure, board A and board B are placed at both ends of the lamp holder respectively). They are sold together with lamp holders for easy installation. Just plug in the lamp and connect the power supply, and you can use it. However, the failure rate of cheap electronic ballasts is high, especially in places with large fluctuations in mains electricity. In fact, only one or several parts of the same brand are damaged due to poor quality and can still be used after maintenance. The mapping circuit is shown in the attached figure (most electronic ballast circuits assembled with discrete components are similar for reference). Some quick repair methods of electronic ballasts are summarized as follows:

First, the preparation work before maintenance

The electronic ballast is directly rectified by commercial power, and then half-bridge inverter is used to light fluorescent tubes. Not isolated from the mains, just like the ironing board of a TV set, the circuit board is charged everywhere, and the human body is in danger of getting an electric shock when touching the public * * * wire (ground wire), so special attention should be paid to personal safety during maintenance. Don't touch any metal parts on the circuit board with your hands, especially don't hold the circuit board with your hands.

During maintenance, remove the lamp tube, take out two circuit boards A and B from the plastic covers at the two ends of the lamp holder R, weld the four wires of the filament spring piece 1-4, and weld them to the filament pins at the two ends of the lamp tube in turn, and connect the switch SWi and the power plug at the mains lead. It is necessary to connect 5w 1. In the process of maintenance, the author found that the electronic ballast was damaged many times in the process of plug-in and power-on, because there were many times of on-off in the process of plug-in, which would produce very high sharp pulse voltage to breakdown vulnerable components.

Second, the maintenance steps

1. The most common failure of fluorescent lamp is that the lamp tube is not lit and there is no response when the light is turned on. First, measure whether R0 is burnt out. RO itself plays a safety role, and once it flows, it will burn out, so as not to damage more parts. Some ballasts are connected to 0 at RO. 5A safety tube. If RO burns out, it must be an overcurrent fault. Replace R05 inch and disconnect at A (see attached figure). Measured by pointer multimeter Rx 10k, the resistance at both ends of the power lead should be greater than 2mf (the series value of r1+R2). So should the test of adjusting the stylus. If there are two, one diode in the rectifier bridge is burnt out; If it is less than 2Md2, C 1 and C2 will leak; If this resistance meets the requirements, it can be measured by electricity. There should be a DC voltage of about 300V between A and B, but sometimes it will burn RO when it is electrified. This is a short-circuited diode in the rectifier bridge. The forward and reverse resistances of D 1-D4 should be measured one by one. The probability of rectifier diode damage is very small, but the filter capacitor damage is more. Especially as shown in the attached figure, if C 1 and C2 are used in series, it will cause a chain reaction, one capacitor will break down and the other will be damaged. When replacing, it is best to choose a capacitor with withstand voltage of 300 V.

2. After confirming that the rectifier and filter circuits are good, start to check the following circuits. Because point A is disconnected, use multimeter RX 10k to measure the resistance between point A and point B (red probe connected to B, black probe connected to A), which should be greater than 500kSZ. If it is 00, check whether the c-e poles of R 10 and VT2 are burnt out; If it is about 470kn, there is serious leakage or even short circuit between the c-e poles of VT2. Here is a question that is easy to be misjudged. When the resistance between Ba "A and B is only about 30kf, it seems that VT2 is leaking, but it is not, because it is 1? In the measurement of OkS2 block, the voltage of 9V in the table is added between A and B, and the bias current is injected into VT2, which is in the conducting state, so the resistance between C and E is very small, not a leakage.

3. After determining that the resistance between A and B is correct, measure the resistance of two PN junctions, vt 1 and VT2, with a multimeter Rxlk to roughly judge the performance of these two triodes. It should be noted that when measuring the PN junction resistance of VT 1, R5 must be disconnected to get a correct reading. Rxl is used to measure the resistance from R5 to 1 1 10. These resistors are all burnt out. Blowing out 1 19,110 is more common. If these two resistors are used for a long time, the resistance will increase. As long as their values are greater than 2dZ, the circuit will not start to vibrate easily and the lights will not light up, so it is important to check. D5, D6 and C4 have high withstand voltage, and Trl winding of magnetic ring transformer has large wire diameter, good insulation and is not easy to be damaged.

4. After the above static measurement, check the faulty components, restore the circuit, and carefully check whether the solder joints and components on the circuit board are short-circuited, bruised, loose or broken. Power on after calibration. In most cases, fluorescent lamps can resume normal operation, but the following failures may occur and should be eliminated one by one.

Overcurrent still appears at (1), and RO continues to burn. This is mainly due to the c-e voltage drop of VT 1 or VT2, and there is high-voltage soft breakdown, so the transistor with sufficient withstand voltage must be selected when replacing it. In addition, the withstand voltage of C3 or C5 is insufficient, which can't be detected by multimeter. It is best to measure the insulation resistance with a 500V shaking table under welding, otherwise it will be regarded as leakage.

(2) Both ends of the lamp tube are red, and the brightness is obviously insufficient. At this time, first measure the voltage at both ends of the lamp tube with the AC block of the multimeter, which should be about100V. This is only a reference value, not an actual number, because the voltage waveform at both ends of the lamp is not a standard sine wave, and the frequency is above 20kHz, which exceeds the frequency response range of the multimeter. If this voltage is lower than 100V, it may be that the performance of VT 1 or VT2 is degraded and the conduction degree is insufficient. In the absence of an oscilloscope, the b-e voltage of the two tubes is about 0.4V measured by a digital multimeter. If the deviation is too large, even positive, it means that the lamp tube is not in a saturated conduction state, so it is advisable to change the lamp tube for testing, and do not blindly adjust the circuit.

If the terminal voltage of the lamp has reached 100V, it still emits light abnormally, which means that the lamp performance is poor. Usually, the quality of fluorescent tubes is judged only by measuring their filament resistance. If the filament is not broken and there is no large area of blackening in the tube, it is regarded as intact. Although the filament of the inferior lamp tube is not broken and there is no trace of blackening in the tube, it cannot be used normally.

(3) The brightness of the lamp tube is insufficient, and there is a spiral aperture in the tube. This is because the current flowing through the lamp tube is small. The main reason is that the production capacity of C5 has dropped too much. Try to connect a 2.2nF 1630V capacitor across C5. In various brands of electronic ballasts, the capacity of resonant capacitor C5 is different, which is roughly between 3- 10nF. If the capacity is too large or too small, the lamp will not shine normally. ?

Three:

Maintenance of electronic ballast for energy-saving lamps

The electronic ballasts of several energy-saving lamps may be burnt out because of high voltage. The circuit diagram is as follows: the damaged components include rectifier diode, filter capacitor, fuse, switch tube and so on. When maintaining, grasp the principle of high component parameters, replace higher-grade components, and then observe the after-effect after maintenance.

Four: maintenance methods of electronic ballasts for energy-saving lamps To maintain electronic energy-saving lamps, we must first eliminate false faults. It is not the quality of the lamp that the energy-saving lamp flashes intermittently after turning off the light. The main reason is that the electrical wiring installation is not standardized and the switch is located at the zero line. Just change the neutral line into the live line. When using a switch with neon lights, a micro-flow path can still be formed after turning off the lights, or a double switch is installed with wires, which sometimes causes flicker after turning off the lights. When repairing electronic energy-saving lamps, for the sake of safety, use 1: 1 isolation transformer to isolate the mains electricity. First, the light doesn't work properly. Fix 1. Common ones are C6 breakdown (short circuit) or voltage breakdown reduction (soft breakdown) of resonant capacitor, so it should be replaced with high-quality polyester or CBB capacitor with the same capacity with breakdown voltage above 1kV. 2. The filament is open. If the lamp tube is not seriously blackened, a 0.047 μ f/400 V polyester capacitor can be connected in parallel at both ends of the broken wire lamp pin for emergency use. 3. If R 1 and R2 are open or have variable resistance values (generally R 1 is more likely to fail), replace them with 1/4W high-quality resistors with the same resistance values. 4. The triode is open. If it is found that only one triode is open, but one transistor cannot be replaced, a pair of switches of the same model with withstand voltage above 400V should be replaced. Otherwise, it is easy for the lamp to roll again or burn the pipe. 5. The light is flashing. If the lamp tube is not seriously blackened, check D5 and D6 for virtual welding or open circuit. If D5 and D6 are soft-broken, or the filter capacitor C 1 is defective, the light will also flash. 6. The lamp is very difficult, sometimes it can be lit by touching the lamp tube or the lamp will roll. This may be because C3 and C4 are insufficient and do not match. 7. If the filament of a single low-power energy-saving lamp is red or glowing after lighting, check whether there is soft fault in D 1 ~ D4, whether there is reverse connection or leakage in C 1, and whether there is short circuit in the power supply part. 8. The cores of choke coil L and oscillating transformer B are damaged. If you only change the magnetic core, you should pay attention to three points: (1) use the magnetic core that meets the requirements, otherwise the inductance value of the choke coil may be very different, which will bury hidden dangers for the energy-saving lamp; (2) The magnetic gap should not be too small to avoid magnetic saturation; (3) After the magnetic gap is padded with suitable filler, it is bonded with adhesive and wrapped with high temperature resistant and flame retardant adhesive tape to prevent looseness. In addition, you can't connect the terminal with the same name of B by mistake. 9. When repairing the electronic ballast using trigger tube, the bidirectional trigger diode should be mainly checked. The tube is generally DB3 type with a bidirectional breakdown voltage of 32 4V. Ii. Maintenance of parts with obvious damage 1. Although the fuse is not blown, the wire at the incoming line is not burnt out, and the resistance is obviously damaged, the triode will undoubtedly be damaged. This may be caused by the aging of the lamp tube, followed by the poor use environment, or the loss of C 1 capacity. For the first two cases, when replacing the resistor and triode, it is best to replace the matching C3 and C4 small electrolysis. For the latter, C3 and C4 need not be substituted. Because C 1 works at high voltage, it is necessary to choose high-quality heat-resistant electrolytic capacitors when replacing it. 2. If C 1, Q 1 and Q2 are intact in the case of fuse and incoming wire, it is necessary to carry out routine inspection and withstand voltage test on D 1 ~ D4 one by one. Or replace D 1 ~ D4 with high-quality products. 3.C 1 burst. If there are fuses and broken wires, all D 1 ~ D4 and C 1 should be replaced. 4. If only the resistor-capacitor on Q2 side and the triode are burnt out, check whether C2 is broken down. 5. If the high-frequency transformer B is damaged, a high-strength wire of ∮ 0.32 mm can be wound on the high-frequency magnetic ring of 10mm×6mm×5mm, with 4 turns for T 1 and T2 respectively; T3 is 8 laps (pay attention to the head and tail). Choke l: lamp power is 5 ~ 40W, corresponding to1.5 ~ 5.5mh. Third, a few electronic energy-saving lamps interfere with remote control color TV. The inductance of L or the capacitance of C2 can be adjusted so that it will not interfere with the remote control TV and can work safely. Four. Precautions for using energy-saving lamps 1. Energy-saving lamps cannot be used in the circuits of dimming desk lamps, delay switches and induction switches. 2. Avoid using in high temperature and high humidity environment. 3. Electronic energy-saving lamps, like other lighting lamps, should not be turned on and off frequently.