Re: resistor transistor basics



Jan Nielsen wrote:

I have several LEDs that use the same voltage, they will be on and off
at different times, so the current usage will not be the same, can they
still share a resistor, when they are in parallel to the resistor ?

Also can a transistor be used to switch a lower voltage than the control?
If not would a simple resistor before the base (green line) help ?

I have a drawing of my idea
http://codebin.dk/stuff/resistor_transistor_basics.jpg
The 100R matches 0.02A (each led) with a 2V drop from supply to the LED.

If you turn on and off each LED with a transistor in parallel with it that
'shorts out' the LED to turn it off, you can run several LEDs in series from a
single current source. The number you can run this way depends on the supply
voltage available of course. I have run up to 16 LEDS this way for example
(audio signal level meter).

This is an excellent way of saving power.

Graham

.

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