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The BJT was my first solution but if I use a MOS-FET, the voltage drop wil be much lower.Analog said:What's wrong with a bjt?
I use 3XNICd @1Ah. The led's I have (10mm @50ma) can be conected without a resistor to 4.3V for short periods. I'l try to keep the circuit as simple&smaller as posible (so no smps chips). The bat will give me a bit more then 3.6V most of the time.philba said:ok, it's question time...
what kind of cells are you using? I suspect you will have higher than 3V with 3 cells. why do you care about switching? for dimming?
I would think your primary concern is getting the longest life out of your batteries. any voltage over the Vf of the LEDs is wasted unless you use something like a DC-DC converter that outputs at the LEDs Vf (or slightly above). there are lots of switch mode chips made to power LEDs with a varying input voltage and very high effeciency. With one of those, you can probably drive the LEDs until the batteries are sucked dry.... You will get a lot more light that way.
Yup. This seems to be the ideea. But if the voltage drop is to high i'l use a BJT.kchriste said:Look for a logic level MosFET. Something like an IRLZ44 meets it rated Rds-On spec at 4V and looks like it'll conduct well enough at 3V to drive LEDs.
The ideea is to build a eficient lamp, not necesary the smalest.justDIY said:another job for the joule thief!
**broken link removed**