Delayed light circuit using relay (7)

We also use a PTC thermistor as the control component to make the circuit
simple. SR1 and SB2 are light-on buttons installed in two different places, both of which can operate the street light
E. When you need to turn on the light,
    just connect SJ31 or SB2.
At the beginning, the resistance of the PTC thermistor is very small, only a few 1
ohm, so the current passes through F, PTC, VD1, VIⅪ and K, so that the lamp E is energized and glows, and the brightness is close to normal. The light when it shines. At this time, the alternating current is rectified by VD1, (, filtered and shunted by hard R for one cycle, so that the relay K can obtain the normal working voltage. , the lamp E can still keep the TF light. When the lamp F is lit for about 25 seconds, the resistance value increases due to the increase in the heating temperature of the PTC element. The current flowing through the lamp E decreases and the brightness weakens, and eventually the relay K cannot maintain Pull in, the contact k-! returns to tripping, and the light goes out.     K should use JRX-26F type small electromagnetic relay , R is a 3W wire-wound resistor, (, is a CDll-16V ordinary electrolytic capacitor. PTC uses color TV Degaussing resistor, such as M272-18 type, etc.