Help, can some one explain MODES?

[Troop#26]

Hi guys,

This should be a rather simple question. I understand how a regulated light can have modes, the boost/buck driver controls how many amps it puts to the LED thus maintaining uniformity across the run of the battery until it drops to no power left in the cell, thus creating table top regulation.

Is there such thing as Direct Drive multi-mode? If so how does it work? I guess my question is can you have an unregulated multi-mode light? And for my own hair pulling understanding, if a light is regulated between say 6 and 9 volt and we run it off a single lithium ion cell (4.2 volts when not under load) how do the multi-modes work?

Thanks

Stephen

 

[AnAppleSnail]

Is there such thing as Direct Drive multi-mode? If so how does it work? I guess my question is can you have an unregulated multi-mode light? And for my own hair pulling understanding, if a light is regulated between say 6 and 9 volt and we run it off a single lithium ion cell (4.2 volts when not under load) how do the multi-modes work?

Thanks

Stephen

It's called PWM. Have the LED on for a certain fraction of the time. For example, it might cycle on/off 10 times per second, staying on for .02 seconds and off for .08 seconds. This is a 20% duty cycle - or 20% brightness. Low-speed PWM visibly flickers, which is annoying. Some buck or boost drivers have one current setting and PWM it to get lower modes.

As for behavior out of regulation voltage, it depends on the electronics. Some lights are dim on low-voltage, some won't light. Some have all the modes less bright, others won't reach high modes. In fact, some lights work fine on a bit too much voltage, but all modes are brighter. Others lose lower modes while over-voltage. Always be careful when over regulation voltage, it's an effective way to kill a good light.

 

[Quension]

EDIT: Sorry AnAppleSnail, timing is everything. Consider this reinforcement

I understand how a regulated light can have modes, the boost/buck driver controls how many amps it puts to the LED thus maintaining uniformity across the run of the battery until it drops to no power left in the cell, thus creating table top regulation.

You're describing current regulation here.

Is there such thing as Direct Drive multi-mode? If so how does it work?

Sort of, depending on context. Not all multimode lights use current regulation to control brightness; some use PWM instead. With PWM, full power from the driver is always supplied to the LED in the "on" stage of the modulation.

"Direct Drive" comes into this in when considering many of the smaller lights, like single-AAA keychain style (Preon, ITP A3, Maratac, etc). These have a boost circuit intended to get the 1.5V supply of alkalines up to the LED's Vf, usually just above 3V. When supplied with a Li-ion at 3.7V or higher, the "boost" part of circuit is essentially bypassed, and people tend to call this direct drive since the LED is getting the battery's high voltage directly. However, PWM is still in effect in order to provide multiple modes -- it's just that all of them are brighter than normal since the LED is being overdriven while "on". (They still work only because the rest of the electronics can actually handle this voltage. Not all PWM-based lights work this way.)

I guess my question is can you have an unregulated multi-mode light?

You might call the lights mentioned above "unregulated" in a sense, as their simple boost drivers do provide multiple modes but actual brightness varies based on the input voltage. They don't have flat output even when using their intended battery types.

And for my own hair pulling understanding, if a light is regulated between say 6 and 9 volt and we run it off a single lithium ion cell (4.2 volts when not under load) how do the multi-modes work?

Depending on the driver and LED configuration, it probably won't turn on. Some may stick at the lowest output level or be very dim on all modes instead.