If you require 9v to 12v output, you will need to add the four voltage-regulating components shown in the diagram below.
The voltage-regulation components added, the circuit produces a 9v or 12v output. This arrangement is only suitable if you have a constant, reliable, source of sun as any clouds will reduce the output to below the regulated voltage. (If a 9v1 zener diode is fitted, the output voltage will be 9v.) The BC 547 prevents the ZXT 851 oscillator transistor turning on when the voltage is slightly above 12v (or 9v). The 10u on the output stores the “reference voltage” and keeps the BC 547 turned on during the time when the output voltage is above 12v. This effectively stops the oscillator, but as soon as the output voltage drops below 12v, the circuit comes back into operation, “charge-pumping” the 10u on the output
The 12v zener works like this: No voltage appears on the anode end (the end connected to the 100R resistor) until 12v is on the cathode. Any voltage above 12v appears on the anode and this voltage passes through the 100R to the base of the BC 547. For instance, if 12.5v is on the cathode, 0.5v will appear on the anode. When the base sees 0.7v, the transistor turns on, so slightly more than 12.7v is needed to turn on the transistor.
The regulation components are not really necessary as a reliable output will only be present when strong sunlight is seen by the solar panel. For the cost of a rechargeable battery or set of rechargeable cells, you get a much more reliable arrangement by removing the regulation components, using the first circuit in the article, and allowing the battery to deliver the 9v or 12v. The battery appears as a HUGE electrolytic on the output, delivering a constant voltage and is capable of delivering a high current.
Read More Source :
http://www.talkingelectronics.com/projects/SolarCharger/SolarCharger.html
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This entry was posted on Friday, August 3rd, 2007 at 10:22 am and is filed under dc converter, switching power supply.
