A light load LED driver

Space Varmint said:

OK, both you all. All I did was build an emitter follower amplifier and replace RE with an LED. That simple. If I drive the base with the supply, the base bias will do the current limiting.

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The purpose of my post was to show that (A) I personally have not seen this done before and so I wanted to demonstrate that the common transistor switch configuration (driving a Xsistor into hard saturation) is not the only method to drive an LED.

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And (B) it puts a light load on the driving circuits. I have had need of the latter in many situations such as tapping of the AC house current, power line and making a small rectifier circuit (no Xformer) to get enough DC to run some logic and ultimately driving a fairly hefty relay which could shut the AC house current off and on. In the voltage converter section I was unable to use anything but an opto-isolator which doesn't have allot of drive. So it would have been nice had I used a buffer circuit to turn on the relay Pre-driver Xsistor.

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But I fail to see how the load is significantly less than having the LED (and resistor) in the collector?

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Yes, no problem at all, just add the RESISTOR

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Space Varmint said:

For one thing, it is a current amplifier and not a voltage amplifier. So there is less load on the voltage which is something I needed for the circuit.

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Nigel Goodwin said:

Do the maths!

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