Hi, it's been long since i have posted a thread, been kinda busy with life but now back into DIY world and i need help for a flashlight project.
I'm looking for a decent circuit of a push to On/Off circuit. I have designed an awesome flashlight of wood, but I'm having problem with a switch.
I don't like mechanical switches as most of them wear out after a few weeks of use. So any of you experts know any simple reliable circuit, preferably using just transistors or an IC that is commonly available?
My flashlight battery voltage is 3.7 V and 1 A. My circuit has posted here. Thanks in advance
Hy Ziddik,
Would you prefer two switches for turning your torch on and off: one switch for on and another switch for off. I personally hate toggle switches for controlling absolute states. The switch could be either mechanical contacts, semiconductor (hall effect magneto resistance etc), or touch. The former has a relatively short life, not just because of contact wear/fouling, but also because of the generally poor mechanical design of contact switches. The latter relies on capacitive coupling of your finger and would probably not be best for a torch and may make it difficult to realise 'zero' current drain in the off state.
As the other members have said, the current through each LED should be defined (300mA). Not only will this give you more overall light, but the light will be more consistent as the battery voltage drops with battery discharge. It will also increase battery duration and prevent the LEDs from being over stressed. Also as the eye has a logarithmic response to light, you may be able to reduce the LED current, if you have a current defining circuit, with little perceptive loss of torch brightness. This would increase the battery duration.
As MikeMI says in post #8, one way to define the LED current would be to use a step up inverter. This approach has a lot going for it because, with the right inverter you you could squeeze the most juice out of the battery. Three drawbacks are the relatively high current required from such a low voltage inverter, the inverter starting problems, especially as the battery discharges and the terminal voltage goes down, and the conversion efficiency, especially in view of the high step up ratio of around 3V to 9V.
Another approach would be to use a constant current generator for each LED, which on balance is probably the simplest for a one-off design, but the drawback is that each LED would only be able to be operated at slightly under 3V max because that is the low discharge voltage for a LiIon cell.
While I have done an outline design for the individual constant current current generator approach, I have not investigated the inverter approach in any detail.
Just to put the current drain of any switching circuit in perspective, the self discharge of a LiIon battery is typically 2.5% per month. Taking an 18650 LiIon battery with a capacity of 2.5AH would give a constant drain current of 20uA (if my calcs are right). This self discharge current goes down at lower temperatures and increases radically at higher temperatures.
I expect you have heard all the warnings about buying second-line batteries with claimed high AH figures, especially those whose marketeers names end in 'fire'. Panasonic (Sanyo) are the best bet for the private individual.
spec
(oh dear I didn't notice the OP date)