Powered with solar panel, the circuit will give you 5V pure regulated DC voltage. This solar cell power supply circuit is made up of an oscillator transistor as well as a regulator transistor. The solar panel charges the battery when sunlight is bright enough to generate a voltage above 1.9v. A diode is necessary between the panel and also the battery as it leaks about 1mA from the battery when it really is not illuminated. The regulator transistor is intended to limit the output voltage to 5v. This voltage will likely be maintained over the capability of the circuit, which is about 10mA.
The oscillator transistor should be a high-current sort as is is turned on for an extremely limited time period to saturate the core of the transformer. This energy is then released as a high-voltage pulse. These pulses are then passed to the electrolytic and appear as a 5v supply, having a capability of about 10mA. If the electric electric current is increased to 15mA, the voltage drops to about 4v.
The transformer is wired to ensure that it gives POSITIVE feedback. The transistor turns on via the 1k resistor and this produces expanding flux inside the core. The flux cuts the turns of the secondary winding and produces a voltage that ADDS to the turn on voltage and also the transistor is turned on A lot more. The transistor gets totally turned ON as well as the electric current via the main becomes a maximum. The core becomes saturated and though the flux is really a maximum, it really is not expanding flux and therefore the secondary produces no voltage (only the voltage and electric current supplied by the battery).
The voltage and electric current into the base of the transistor is decreased, and this cuts down the electric current via the main. The flux now begins to collapse and this produces a voltage in the secondary of an opposite polarity. This turns the transistor OFF and also the magnetic flux collapses shortly and produces a high voltage. This voltage is passed via the diode and charges the electrolytic. The circuit operates at approx 50kHz as well as the pulses shortly charge the electrolytic.
The 15k resistor has a 3k3 “trimmer” resistor to allow you to adjust the output to specifically 5v or slightly above 5v. Microcontrollers will operate up to 5.5v but some will freeze at 5.6v, so be careful. The output voltage is monitored at the join of the 15k resistor (and 3k3) as well as the 2k2 resistor. The voltage at this point is precisely 0.63v (630mV) and at this voltage, the regulator transistor turns ON and robs the oscillator transistor with “turn-on” voltage.
When a load is placed on the output of the circuit, the voltage across the electrolytic drops as well as the regulator turns off slightly. This permits the oscillator transistor to operate “harder” and send pulses of energy to the electrolytic to charge it. If the load is removed, the electric current consumption of the circuit is about 3.5ms. This may be the quiescent current in the circuit.
The output electric current is limited as every mA needs about 5mA from the battery. On 15mA output, the current needed from the battery is about 75mA. That is why we need a high-current capability transistor for the oscillator. A BC 547 transistor won’t function, as it really is not capable of passing a high electric current.
The solar panel will deliver about 10 – 15mA on bright sunlight, so any load on the output should be as small as possible. An example is information logging, exactly where the micro is active for short periods of time, then goes into “sleep” mode.
5V Regulated Solar Cell Power Supply circuit source: talkingelectronics.com