With me messing around with batterys lately this has just intrested me upon digging around for circuit i could try building. Clicky The top one. I understand how it works and why. What i need a hand in is how i can caluclate the required companant i need for a 12V version so it woudl run nicely off a car battery. Few Questions. What voltage can be expected after the zener? VCC minus .6? Do i calculated voltage at the pot wiper arm to the transistor base by simply using the devider equation? I.E R1 is the pot R2 would be the 22K ? The resistors for the other transistors base and the led current limit are fine i can work these out but trying to adapt this for 12 is a little tricky, could some one please advice on the best way to go about it. I want the transistor to turn off at 10.5V to 11V some thing like that tbh. Is there a better way of doing this? Thanks !
Thanks for the good url, iv read that and thats fine. but since that circuit does not use the zena in that fashion i still dont understand the zena --- pot --- resistor Properly? Any other reading that would help please?
The variable resistor and resistor just forms a potential divider. The circuits displayed in the link I gave you do show the circuit you are concerned about, it's just a different looking symbol since a variable resistor set at a certain position is a resistor.
Try changing the zener to the nearest preferred value, say 7.5 volts and increase the value of LED current limiting resistor.
