CC LED Driver

251

03:57:52

Constant current LED driver

Delivers 19.5mA at diode foward voltages from the 0.1V of a germanium signal diode up to a ridiculous 3.8V. (Ridiculous for a simple PN-junction diode, whether LED or anything else.) 

Delivers 19.5mA into a 2.2V LED at power supply voltages from 3.4V to (I presume) transistor breakdown voltage. (Simulation fine at 10kV!)

Switched by a lower current, taking 3.2mA there. Could take less with some adjustment.

The dark LED is merely a voltage reference, it could be replaced by a Zener diode. Current depends on this voltage and the voltage developed across the emitter resistor. The transistor will turn on until the voltage at its emitter is about 0.8V less than at its base.

published 7 years ago

lenzrulz

7 years ago

Good description for a clever idea...👍

jason9

7 years ago

The current of a transistor increases as the voltage from it’s collector to emitter increases. It’s called Early voltage or Early effect and EC doesn’t simulate it. That means that even if the transistor has a breakdown voltage of 200V, driving it at 150V will still add current, probably destroying the LED.

eekee

7 years ago

That makes sense, jason9. It has a lower upper limit, then.

eekee

7 years ago

@lenzrules, thanks! :) Not my idea, i found it in amplifier plans.

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.