Two-level switch resistor question

Can anyone give a technical description of how something like the Surefire two level switches work? I know it's just a resistor, but I was looking for something a little more electrical than "it fools it into thinking the battery's run out"!

I've read a lot about this type of switch, and how you can use them with BadBoys etc., but I tried holding a (39 ohm) resistor to drop the Diamond regulated 1 watt in my Mag and had to let go after a couple of seconds (ouch!).

I'm thinking that with a fully regulated boost circuit, you'd have to drop enough voltage across the resistor for the voltage across the driver to be low enough for it to fall out of regulation, if that makes sense. So, maybe I didn't have a large enough resistor??

Any help/tips very much appreciated!! Thanks!!

Anyone?

You're on the right track.

You need a large enough resistor (in terms of number of ohms) to get the dimming level you want (more ohms, dimmer) and of high enough capacity (Watt rating) to keep from burning your fingers (more Watts, less pain).

Doug Owen

Thanks, Doug. Much appreciated!

Having tried again with a rather better set-up test rig, I measured the circuit (Diamond regulated 1 watt, 2 x lithium AAs, 22 ohm resistor) pulling around 110 mA.

This gives a lot of dimming, but with over 2.5 V being dropped across the resistor there's (obviously) an awful lot of power being loss in it (well, about a third of a watt! Okay with a 0.6 W metal film resistor, though).

I knew this wasn't the most efficient way of acheiving multi levels, but I'm surprised by how much power is actually lost!

I'll have to look for a boost regulator circuit that I can switch the output on, and that drains two cells. Anyone know any lights I can cannibalise for something like this???