How long would a 150 Farad Capacitor light up an LED?
There is at least one well-thought out answer to the question in the replies.
Another interesting application for those solar cell to USB charger modules I see on the web.
Amazing answer, thanks for sharing!
During the weekend I will update the thread with my tests :) Thanks again
Ok guys, I tried! If I directly connect the PNP base to battery negative the LED lights up as bright as possible but it never turns off, even if I put everything in the sun. If I add a 5k resistor between PNP base and battery negative it works as ex pected, so it automatically turn on and off according to the amount of ligh t on the solar panel, but the led brightness is not much even when I cover the panel or if I disconnect it. Ideas?
Thanks a lot!
Changing the transformer so the top end of the winding that goes from the PNP collector to the NPN collector instead is connected from pattery positive to NPN collector will improve brightness.
Leave the winding that goes from PNP collector to the resistor that goes to the NPN base connected to the PNP collector and resistor
-- Jasen.
Have you tried looking for a happy medium resistance? You want to turn on the PNP and drive it into saturation (ideally) and have it turn off when the panel is making electricity.
It is never good practice to connect the base of a bipolar transistor to forward bias it without some current limiting resistor. If your transistor survived, it is only because the battery wasn't powerful enough to fry it.
The ideal size resistor depends on the current gain of the transistor. Gain is specified at a particular collector current in the datasheet and there may be a graph too.
Small signal transistors usually have gains of ~100. So with 1 milliamp flowing in the base you should get 100 in the collector circuit. (more or less... gains can be specified as some minimum and the maximum, for a production run of parts, can be several times higher)
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