Electronic – Using PNP as OFF switch

ledsolar cellswitches

I am a total novice but not unintelligent. I want to use a single solar panel to switch on some lights when it gets dark and also charge the batteries for the lights. I have previously successfully done this using a JFET, but have to have TWO solar panels, one to switch off the JFET and one to charge the batteries. I have read on numerous web sites that I can use a PNP transistor. As far as I can understand it they ALL say that a PNP is ON except when a base current is applied. Example circuits are shown. I have bought quite a few PNPs, different values. I have tried all of them in the suggested circuits. I have tried all of them with just a battery and a bulb. None of my PNPs are on with no base current, they all only switch on when I apply a current to the base. This is the opposite of what all these sites are saying. What am I not understanding? Connect battery +ve to PNP emitter, connect pnp collector to +ve of LED, connect -ve LED to -ve battery NO light.
Connect -v of solar to pnp collector and +ve of solar to pnp base and LIGHT. This is the exact opposite of what I want. What am I doing wrong

Best Answer

To switch on any transistor PNP/NPN, you need to forward bias the base emitter junction

so for PNP emitter is +ve and base is -ve so to forward bias connect emitter to +ve supply and base to ground with resistor (see attached image)

similarly for NPN connect emitter to GND and supply +ve voltage to base

PNP-NPN

Note: the explanation are purposely made simple for understanding purpose

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