Converting 2.4V to 3.6V in torches

[varunme]

How 2.4V is converted to 3.6V in LED torches to lignt a 3.6V led ?

 

[picgak]

by using a small boost converter circuit

 

[varunme]

is it energy efficient ?

 

[kripacharya]

you can even convert 1v -- even 0.5v -- to light 3.6v LED (which led is this btw ?)
google for 'joule thief' circuits

 

[varunme]

1w led which uses 3.6V

 

[picgak]

Hi varunme,
The boost converter is highly efficient with wide input rating from 0.7 V to 5.5 V with a few components see the link given below
https://www.ti.com/lit/ds/symlink/tps61220.pdf

 

[cntube]

I have seen torches with simple boost circuits, inductor and bjt's fedback with a capacitor to make oscillator. The current is set by leakage inductance and inductor on-time for discontinuous current. With the boost voltage clamped by the LED's own VI characteristics. Actually one 1.5V cell is enough for bipolar based designs.

 

[BradtheRad]

The 3909 IC flashed an led from a single 1.5V battery. It charged a capacitor, then switched its polarity to add to the supplyV, thus is could power a 1.8V led.

The 3909 is obsolete because the same function apparently can be duplicated by more advanced circuits and IC's (although I don't know what number to look for).