Introduction and troubleshooting of fiber optic lamps (half-bridge transformer circuit diagram)

Fiber optic lamp is a unique decorative lamp. It is mostly used in bars, nightclubs, high-end hotels and other places. This lamp cleverly uses the light-guiding properties of optical fiber bundles or rods. After matching with a special light source machine, strong light is emitted from the light source machine and the optical fiber interface to the optical fiber. The light can be transmitted along the optical fiber, so it can appear in the optical fiber body and terminal (because the distribution and shape of the optical fiber have been designed before); so it will produce strange light effects such as silk waterfalls, starry sky or soft body light shape, and the uniqueness of the effect is not achieved by other decorative lamps.

As one of the important parts of fiber optic lamps, the light source machine is usually calibrated by the power of its light source lamp (such as "R-150, H-100 models, etc., that is, 150w and 100W). With the different power of the light source machine, the light source lamps used in it are also different. For light sources with a power greater than 150W, the machine usually uses a high-voltage xenon lamp as the light source. This type of lamp is composed of an iron core inductive ballast, a trigger and a xenon lamp. When a fault occurs, the accessories are easy to purchase. On the contrary, for light sources with a power less than 150W and below, due to the internal Different from the lamps, most of them use a "high-power" electronic transformer to output Ac12V low voltage. Then drive a special reflective concave mirror type low-voltage halogen tungsten spotlight cup as the light source. The lamp cup and electronic transformer are mostly imported finished devices, so once burned out (especially the electronic transformer part), it is difficult to find a replacement part for maintenance. In this regard, the author took the H-100 light source machine electronic transformer as an example, disassembled it, and mapped its circuit including the external component circuit (as shown in the attached figure) (note that the transformer diagram has a little error) to help the maintenance personnel for reference.

1. Brief analysis of circuit working principle

In the attached figure, the 220V mains voltage is input from the "POWER INPUT" plug, and after passing through the "POWER SWITCH" and "FusE" switches, it is supplied to the two motors M1 and M2 (M1 is a low-power stepping slow-speed motor used to drive the mechanically rotating color-changing filter disk in the light source machine, and M2 is an AC axial flow fan used to drive the air and dissipate heat inside the light source machine).

In the figure, after points "A" to "B", there is the electronic transformer circuit part of the machine. The impurities are filtered out by C1, L1, and C15. After being rectified and filtered by D1 to D4, C2, L2, and C3, a DC voltage of about 350V is obtained. This voltage charges C5 through C4, R2 (R3), and RT2; when the voltage across C5 rises to the turning voltage of D6 tube, D6 avalanche conducts; and a pulse narrow current is given to the base of Q4 transistor b, and Q4 conducts. In this way, the 350V voltage is charged on C4, C5, and the voltage on the loop C10. It is discharged through the primary of transformer B2 and the winding of B1 magnetic ring transformer N1 and the ce pole of Q4 and R16. At the same time, the induction pulses generated on the N2 and N3 windings on B1 are fed back to the bases of Q3 and Q4, turning Q3 on and Q4 off; in this way, the original voltage on C9 is discharged through the primary circuit of Q3 (ce pole), R15, B1 (N1), and B2. Since B1 is induced again, Q4 and Q3 are repeatedly turned on and off (circulated), thus forming an oscillation of about 30kHz. When the oscillating current flows through the primary of the B2 high-frequency transformer, the secondary winding induces a pulse voltage of about 12V, which is supplied to the 12W100W halogen tungsten lamp cup in the light source machine, making it glow.

In addition, in order to make the circuit more stable and reliable, feedback protection circuits composed of Q2 and Q1 tubes are also provided on the b-pole and e-pole circuits of the oscillation circuit Q4. When the voltage of the b-pole of Q4 is abnormal during operation, the voltage drop on R7 will rise synchronously; therefore, the conduction of Q2 increases, and the potential of the b-pole of Q4 is correspondingly lowered, thereby stabilizing the state of Q4. The Q1 protection circuit set in the e-pole link of Q4 has the function that when the current of Q4 increases suddenly due to circuit abnormality, the corresponding increased voltage drop on R16 is saturated by D9, R8, C16, R5, and Q1 (b-pole), so that Q1 is turned on and saturated, thereby "shorting" the voltage across C5 and forcing the oscillation circuit to stop oscillating for protection. Moreover, D5, D7~D12 and other links are used in the circuit to discharge the peak reverse voltage that may be generated by the circuit operation to prevent damage to the Q3 and Q4 oscillation tubes. In addition, the ZM1 and ZM2 varistors set in the power input circuit of this electronic transformer can play an overvoltage protection role for the circuit when the mains power is abnormal.

2. Repair of fault prone

【Example 1】The electronic transformer has no low voltage output.

During the inspection, the temperature protector and R1, D1~D4 were checked first. No abnormality was found. After power was turned on and the two ends of the C3 capacitor were detected, a 350V DC voltage was found (normal power supply), so it was initially determined that the oscillation circuit stopped oscillating. After that, when R3, R2, R7, and D6 were tested after power was turned off, it was found that the temperature protector element RT2 was broken. After replacing RT2 and testing the machine, the light emission returned to normal.

【Example 2】The light source produces a "humming" sound over time.

Maintenance: This phenomenon occurs more frequently on long-used light source machines. During the inspection, it was found that the "hum" sound was emitted from the axial flow fan M2 installed at one end of the host for heat dissipation, and the fan was also accompanied by a deceleration phenomenon. It was judged that the abnormality was probably related to the lack of oil in the motor for a long time. So after removing the fan and peeling off the adhesive paper label at one end, the exposed fan shaft end was dripped with oil to increase lubrication. After this method was used, the original noise disappeared after the machine was retested, and the fan speed and air volume were also restored.