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Topic starter
2019-06-20 8:18 am
Yesterday, I spent all afternoon playing around with a constant current source circuit. Made up of 2 x 200Ω resistors, an NPN 2222 transistor, and a 5.1V Zener Diode.
From the 12V rail through a 200Ω resistor, node to the transistor base and the Zener to ground. On the other side 12V rail through to the load (various number of LEDs) to transistor collector, emitter through 200Ω a resistor to ground.
This setup gave me a constant current of 21mA from about 7V to 15V, with a total circuit consumption of 55mA at 12V.
55mA - 21mA = 34mA pouring through the Zener. What a waste!
Now I can see how it works, could anybody enlighten me of what practical use this circuit has?
Steve
2019-06-20 9:54 am
Hello,
Constant current circuits are useful for driving Leds or other devices that require constant current and for charging lithium cells at constant current. It is also good for experimenting with other circuits which require you to run it at a constant current.
Hope it helps.
hj
2019-06-20 1:10 pm
I like to use an LM317 as it's just 2 components, a resistor and the regulator (may want a capacitor in there too but that's being picky).
Have a look at this
http://www.reuk.co.uk/wordpress/electric-circuit/lm317-current-calculator/
There are low dropout versions too, but experimenting is the way forward.
Have fun releasing the smoke!
Ian
Topic starter
2019-06-21 9:41 am
The LM317 sounds good for practical purposes but I am just trying to find out how all these parts fit together and what happens when I start changing the values of the resisters and Zener diode.
I like to think of myself as a "very small bit" of a Micheal Faraday, who had no formal education but learned by pure experimentation.
Steve