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Step 3How it works
This circuit is rather simple to build and also to understand in principle. To calculate the exact values is a harder task.
How it works:
The trick of this circuit is that the base of T1 is connected to the emitter of T2 and the base of T2 is connected to the collector of T1. So these two transistors rival for the whole current that flows through the LED.
They build something that is called a negative feedback system. A rise in current through T2 would lift the potential at the base of T1, which would then rise the current through T1. With this happening, a part of the current formerly going to the base of T2 would the just directly flow through T1 and as the result the T2 would be closed a bit more and lower the current through it (and the LED).
It's not a perfect regulation because for a rising input-voltage the current also rises slowly, but not too excessive.
To show that it works I tested a few LEDs with it.
Have fun and keep building!
How it works:
The trick of this circuit is that the base of T1 is connected to the emitter of T2 and the base of T2 is connected to the collector of T1. So these two transistors rival for the whole current that flows through the LED.
They build something that is called a negative feedback system. A rise in current through T2 would lift the potential at the base of T1, which would then rise the current through T1. With this happening, a part of the current formerly going to the base of T2 would the just directly flow through T1 and as the result the T2 would be closed a bit more and lower the current through it (and the LED).
It's not a perfect regulation because for a rising input-voltage the current also rises slowly, but not too excessive.
To show that it works I tested a few LEDs with it.
Have fun and keep building!
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