3M-type projector sometimes occur due to voltage fluctuations and transient phenomenon of projection lamp burns out. If the increase to the 3M projector protection circuit shown in Figure 1 can have more to prevent the occurrence of the phenomenon of the projector bulb burns out.
  Work
  Protect the electrical circuit shown in Figure 1, dashed right half, left half of the original wiring for the projector schematic. Closed power switch K, exhaust fan starts rotating M1. Mains voltage by R1, C1 charge for the transformer primary circuit, C1 turns on both ends of the voltage value to VD2, VD2 to work to produce the trigger pulse signal, the VD1 turn, the transformer primary circuit a current flows out of the secondary induction low-voltage alternating current, the projector light bulb is energized. Adjust the resistor R1, the VD1 work in semi-state, that is, the voltage across the transformer primary B1 1 / 2 power supply or so. In order to prevent the full impact of the filament voltage and high current moment, the effective protection of the projector lamp and prolong its service life, while rotating in the M1, 220V voltage through C2, R2 RC buck limit, the gift D1 ~ D4 composed of full-wave full wave circuit, output DC voltage. Both the DC operating voltage for the relay J1, and charging through R3 on the C3. As C3 larger capacity, the voltage across the delay can not produce an instant effect of the formation, after about 1 second, C3 was sufficient to turn-on voltage VD3, VD3 turn, pull the relay J1, normally open contact closure , A short-circuit the anode and cathode VD1 K, B1 started to work in the 220V voltage state, the projector bulb full light, to reach the standard brightness of the projector. R4 VD3 control to protect the role of polar G, but also on the rapid loss of power C3 after discharge, to meet the electronic teaching in the use frequently turn on the projector features

Component selection and installation
  VD1 selected voltage greater than 400V, maximum current of 16A of the triac. VD1 not installed because the heat sink, it should be a larger selection of current models. VD3 selected 1A, 400V single SCR. J1 use the contact current 10A, voltage of 12V, the contact is 1 × 1 single set of relay contacts. Should not use 2 × 1 or 2 × 2 dual sets of contacts of the relay, to prevent the relay timely because of the elastic reed contact is closed due to the difference of sync caused sparks of contact life. Other components of the parameters are chosen according to drawings marked. Be sure to buy genuine components.
  After a simple measurement of components can be assembled. Component assembly should be in accordance with the first low-high, after the first large program for small. After the assembly for final assembly and debugging. 4A fuse on the transformer output power compared with the exhaust fan and then remove the card, cut 2 / 3 length, leaving 1 / 3 wire soldered to the circuit board B Department, cut 2 / 3 of wire soldered to a circuit C at the plate, the other end of the card into the adapter card column. 4A fuse output lines cut 2 / 3 length, leaving 1 / 3 wire soldered to the circuit board A place. Length of about 20cm or so to find a plastic wire, soldered to a circuit board D Department, a head welded to the adapter card of another column. Check the components of the welding and wiring is correct, you can power debugging. The circuit board fixed in the 4A fuse on the fan base is above the office, plug in the power supply, 250V AC voltage with a multimeter block measuring the voltage across the transformer primary B1. Toggle power switch, hands indicating the value should be around 110V, this time the lamp is half bright, shiny red. If voltage is high and should cut off the power, unplug the projector plug, replace the slightly larger resistance the resistance R1.
  After adjusting resistor R1 power, the bulb is about 1 second after the half-light, J1 relay should pull, all light bulbs. R3 resistance adjustment can change the light bulbs warm (half lit) Time: R3 resistance increases, the delay time increase. Delay should not be stressed too long, so an increase of power consumption and heat would VD1, two do not facilitate the practical use. The values shown in Figure 1, the delay time is about 1 second. Through the commissioning, the circuit works properly, the projector can be put into use. The device in the restructuring of the use of multiple projectors more than 1 year, the results are satisfactory, the projector bulb phenomenon there have not been damaged.