PWM vs linear driver | Candle Power Flashlight Forum

A linear driver reduces power by putting in a resistor. The advantages of this are price and size, the disadvantages waste of energy (converted into heat by the resistor) and non-regulated nature of the output, i. e. when battery voltage decreases the light becomes less bright.
PWM swiches the light on and off, and the brightness depends on the ratio of on and off times. This is more efficient, because in each of these switch positions (almost) no energy is taken from the battery that does not go to the LED. And in combination with a microcontroller better controls can be implemented, e. g. many levels of brightness, programmable brightness and regulated brightness. (I do not know if there are lights with PWM but without regulation.)
Disadvantages of PWM are price, size and, if not that well designed or manufactured, under certain circumstances they might emit sound.

thanks, that really cleared things up!
I was unsure which one to these to use for my XM-L modding project but now I will definitely go for the PWM Driver!
http://www.shiningbeam.com/servlet/the-132/3-dsh-Mode-Regulated-Circuit-Board/Detail
http://www.lck-led.com/p846/Constan...-5-Mode,-3.3-4.5V-Max.-3.0A/product_info.html
BTW, price and size of the PWM driver is about the same as on the linear one in this case.

thanks, that really cleared things up!
I was unsure which one to these to use for my XM-L modding project but now I will definitely go for the PWM Driver!
http://www.shiningbeam.com/servlet/the-132/3-dsh-Mode-Regulated-Circuit-Board/Detail
http://www.lck-led.com/p846/Constan...-5-Mode,-3.3-4.5V-Max.-3.0A/product_info.html
BTW, price and size of the PWM driver is about the same as on the linear one in this case.

Is the SB driver clearly not a PWM driver? It doesn't seem to say.

Also, based on the info for the PWM driver:

Testing CSX0I P7 LED
Vin(V) Iout(A)
4.1 3.3
4.0 3
3.9 2.9
3.8 2.7
3.7 2.3
3.6 2
3.5 1.7
3.4 1.4
3.3 1.2

Doesn't the diminishing current seem to imply that it's a linear driver and not PWM?

I'm asking because I'm trying to figure out all this mumbo jumbo for myself as well...not trying to be annoying ???? There seems to be a lot of difference between advertised features and actual features in this industry. I think there are some things not clear in this thread:

A) METHOD OF CONTROLLING CURRENT

- 1) Resistor: Highly variable output current w.r.t. battery voltage and LED voltage. Lots of loss at high voltage, not as much at low voltage.
- 2) Linear Current Regulator. Same current no matter what battery/led voltage as long as battery voltage > LED voltage. Lots of loss at high voltage, not as much at low voltage.
- 3) Switch mode current regulator. Same current no matter batter/led voltage. Low losses across battery voltage.


B) METHOD OF ADJUSTING BRIGHTNESS

- 1) Adjust the current - Can be done by adjusting the resistor or changing the current for either a linear or switching current regulator
- 2) PWM the OUTPUT - Which can be used with a resistor, a linear regulator, or a switch mode regulator


Where the confusion can come in is that a PWM circuit is used in inside many switch mode regulators. However, don't confuse the method used to control current and the method used to adjust current.

Last, if you PWM high enough, there is not a person on the planet that will be able to tell the difference. Yes there are certainly differences in optical processing speeds and that is why some people notice low speed flicker more. They also had issues with color wheel based DLP projectors that used low rotation speeds. However, crank up the speed up high enough and it is physically impossible to notice. I also have issues with low frequency dimming. Even 100 Hz I find problematic. I "think" I can still notice a bit a 200Hz, at least when I know it is. Past that, no nothing. Hz PWM is not uncommon now. Higher frequencies make issues with movement based modulation go away too.

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