Solar lawn Light circuit principle is relatively simple. Its controller is implemented using a boost circuit.
BT1 selected two 1.2V / 600mA Ni-Cd battery, such as the need to increase the luminosity or extended time, can be increased accordingly Solar panels and battery power. VQ2, VQ3, VQ5 β in about 200, VQ4 need to β large value of the transistor. VD1 try to choose the tube down, Solar lawn Light such as germanium tube or Schottky diode. LED can choose white, blue, green ultra-high brightness astigmatism or condenser. When you use red and yellow orange and other low pressure drop LED, the circuit needs to be reset. R3, R5 recommended the use of 1% precision resistance; R4 with bright resistance 10kΩ ~ 20kΩ, dark resistance 1MΩ above the photosensitive resistor. Solar lawn Light Other resistors can use ordinary carbon film (1/4) W, (1/8) W resistance. L1 with (1/4) W color inductor, DC impedance is small.
The working principle of the circuit: the day when there is sunlight, the BT1 by the light energy into electricity, by the VD1 BT2 charge, due to light, photoresistor was low resistance, VQ4 b very low and cut off. VQ4 is very low level also conduction, by the VQ3, VQ5, C2, R6, L1 composed of DC boost circuit work, LED power to light.
DC boost circuit is the core of a complementary tube oscillation circuit, the work process: VQ2 conduction power through L1, R6, VQ4 to C2 charge, because C2 voltage can not be changed at both ends, VQ3 b is extremely high, VQ3 not Conduction, with the C2 charge of its voltage drop higher and higher, Solar lawn Light VQ3 b pole potential is getting lower and lower, when low to VQ3 conduction voltage VQ3 conduction, VQ5 have conduction, C2 through VQ5 ce knot, power, VQ3 eb junction (due to VQ2 conduction, we assume that its ec junction short circuit, VQ3 e pole direct power supply positive) discharge.
When the VQ5 is turned off, VQ5 is turned off, the power supply is charged again to C2, and then VQ3 is turned on, VQ5 is on and C2 is discharged, so that the circuit is oscillating. When the VQ5 is turned on, the power is supplied through L1 and VQ5 ce to the ground, the current through the L1 energy storage, Solar lawn Light VQ5 cut off when the L1 induced electromotive force, and power superimposed after driving LED, LED light. This can improve the battery voltage directly to drive the LED to improve efficiency, but the battery voltage increases, the corresponding price of solar cells has increased significantly, as long as the circuit components set the right, its efficiency is acceptable. When the daytime charge is not enough (in case of rainy days, etc.), BT2 may have occurred discharge, this will damage the battery, for this special R5 constitute over-discharge protection: When the battery voltage dropped to 2V, Solar lawn Light due to R5 partial pressure to VQ4 The base potential is not sufficient to turn VQ4 on, thereby protecting the battery. Increasing R5 affects the conduction depth of VQ4.