Maintenance and improvement of fire emergency lights
A batch of Taiyuan TY06 fire emergency lights showed no charging indication after several months of use. The phenomenon that the light cannot be turned on. Analyze its circuit as shown in the figure.
The commercial power is bucked and limited by capacitor C1 (about 100mA), filtered and rectified to charge the battery with constant current. At this time, the potential of point A is about 7v, and the voltage divided by R3 and R5 provides a bias for the base of Q1, so that Q1 is turned on. However, the base of Q2 is clamped by D6 and the emitter is at the same potential and cut off, so the base of Q3 is cut off without bias current, and the lighting lamp does not light up. When the mains power is cut off or the test button K1 is pressed. The potential at point A drops. D5 and D6 are off, and Q1 is still turned on under the action of C3, so that after Q2 is turned on, Q1 is kept on through D7 and R4, and Q3 is turned on through R8, and the light is on. At this time, if K2 is pressed, Q1 is cut off without bias, and the lights of Q2 and Q3 are cut off, and the light-off function is completed. For example, when K3 is pressed again, Q2 is turned on, and Q1 and Q3 are turned on through D7, R4 and R8. And Q1 is turned on and Q2 is kept on, the light is on, and the light-on function is completed.
Checked. The damaged circuits are all R2, R7 burnt, C2 burst, or the battery liquid of the lead-acid battery is dry and damaged. Can no longer be charged. Analysis of the cause of the failure is that the battery has been charged for a long time and the battery fluid has dried up. Cause the voltage at point A to rise and damage the above components. Since the emergency light does not move, replace its maintenance-free battery with a common battery. After replacing the damaged components, the emergency light can be used normally. In order to enable it to be used for a long time, the constant current charging is changed to floating charging, and a 7V/1W voltage regulator is used in series with a 33Ω resistor and then connected between point A and the ground. After more than one year of use, it is normal.
