In the previous article we discussed the charger controller, the battery high/Low controller and the light sensor sections of the proposed 40 watt automatic solar street light system circuit.
This page will show you the making procedure of the PWM controlled LED module circuit.
The circuit shown below represents the LED lamp module consisting of 39 nos. 1 watt/350 mA high bright power LEDs.The whole array is made by connecting 13 number of series connections in parallel, consisting of 3 LEDs in each series.
The above arrangement of LEDs is pretty standard in its configuration and does not focus much importance.
The actual crucial part of this circuit is the IC 555 section, which is configured in its typical astable multivibrator mode.
In this mode the output pin#3 of the IC generates definite PWM wave-forms which can be adjusted by setting the duty cycle of the IC appropriately.
The duty cycle of this configuration is adjusted by setting P1 as per ones preference.
Since the setting of P1 also decides the illumination level of the LEDs, should be done carefully to produce the most optimal results from the LEDs. P1 also becomes the dimming control of the LED module.
The inclusion of the PWM design here plays the key role as it drastically reduces the power consumption of the connected LEDs.
If the LED module would be connected directly to the battery without the IC 555 stage, the LEDs would have consumed the full specified 36 watts.
With the PWM driver in operation, the LED module now consumes about 1/3rd power only, that is around 12 watts yet extracts the maximum specified illumination from the LEDs.
This happens because, due to the fed PWM pulses the transistor T1 remains ON only for 1/3rd of the normal time period, switching the LEDs for the same shorter length of time, however due to persistence of vision, we find the LEDs to be ON all the time.
The high frequency of the astable makes the illumination very stable and no vibration can be detected even while our vision is in motion.
This module is integrated with the previously discussed solar controller board.
The positive and the negative of the shown circuit needs to be simply connected to the relevant points over the solar controller board.
This concludes the whole explanation of the proposed 40 watt automatic solar LED street lamp circuit project.
If you have any questions, you may express them through your comments.
R1 = 100K
P1 = 100K pot
C1 = 680pF
C2 = 0.01uF
R2 = 4K7
T1 = TIP122
R3----R14 = 10 Ohms, 2watt
LEDs = 1 watt, 350 mA, cool white
IC1 = IC555
In the final prototype the LEDs were mounted on special aluminum based heatsink type PCB, it is strongly recommended, without which the LED life would deteriorate.