Why draw power when light is switched off?

[CoolHands]

I was reading about the Nitecore D10 and noticed

When the light is off, the microprocessor draws very, very little power - between 0.1-0.4ma (0.2ma typical). For example, one 2000mah cell would last about 416 days!

here https://www.4sevens.com/product_info.php?cPath=93&products_id=502

Why is any power used at all? :thinking: I was quite surprised to read that. Do most of the LED torches we read about here use some power even when off? Or does it depend on the switch? (the D10 uses a microprocessor).

just interested

 

[WadeF]

How else would a microprocessor process your clicks if it wasn't drawing a little power? It's not enough power to worry about, unless you leave a battery in your flashlight for 6-12 months and never use it. It may even take longer than that to drain the battery.

This is true for lights that use microprocessor switches. Most lights don't use them and use reverse clickies, forward clickies, twisties, etc, to activate the light. When you work these switches you are simply breaking a connection, or making a connection. So when you break the connection no power is used. With the microprocessor the processor is powered and responds to clicks, which are simply sending a signal to the processor and then the processor tells the light what to do. Well, that's the best way I can describe it.

 

[Illum]

read up on "quiescent current" under biasing, its interesting to note that the current is measured in µA, or micro amps, many circuits draw current at open load...but many times its so minute that you can hook a lemon on to it and it'll still run for days:twothumbs

 

[vali]

Does the "drain" happend even when you have the D10 untwisted?

 

[WadeF]

Does the "drain" happend even when you have the D10 untwisted?

I think untwisting will cut the circuit and stop the power drain.

 

[Jarl]

I think untwisting will cut the circuit and stop the power drain.

Yup. If you have the light set to momentary, there is no connection between the PCB and sleeve, so no current will/can flow

 

[Justin Case]

The OpticsHQ/TLS multifunction tailcap draws about 0.5ma to 1ma. If you back out the tailcap a bit to break the electrical contact, then the draw is zero.

 

[jzmtl]

What makes me wonder is why some light draw a lot more than others. I.e. above mentioned lights draw power in mA range, while novatac draw in uA range and the 123a will actually expire long before being consumed by the processor.

 

[HKJ]

What makes me wonder is why some light draw a lot more than others. I.e. above mentioned lights draw power in mA range, while novatac draw in uA range and the 123a will actually expire long before being consumed by the processor.

A microprocessor in sleep draw very little power, but this depends on the actual programming and the microprocessor. Some microprocessors can just about turn everything off and just wait for a keypress, other needs some oscillator running and that will increase the power consumption.

Usual the settings for a light is stored in EEPROM memory, that can keep the values without needing any power.

But the "big" power consumption is the boost converter, if it has to run to supply the microprocessor (Most likely on 1.5 volt lights), the light will have a rather high standby current (The only 1.5 volt light with really low standby current I have seen is the LF5XT).