Quick question about linear regulators

I bought this linear regulator to power a SSC P7: http://www.shiningbeam.com/servlet/the-132/3-dsh-Mode-Regulated-Circuit-Board/Detail

I read this article about linear regulators from Wikipedia:

in electronics, a linear regulator is a voltage regulator based on an active device (such as a bipolar junction transistor, field effect transistor or vacuum tube) operating in its "linear region" (in contrast, a switching regulator is based on a transistor forced to act as an on/off switch) or passive devices like zener diodes operated in their breakdown region. The regulating device is made to act like a variable resistor, continuously adjusting a voltage divider network to maintain a constant output voltage. It is very inefficient compared to a switched-mode power supply, since it sheds the difference voltage by dissipating heat.

My question is does the linear regulator I bought turn any voltage from the battery higher than the P7's max voltage of ~3.6V into wasted heat energy? I know its not a buck driver so I'm wondering what method it uses to drop voltage. If I use the lower light modes of this regulator, am I extending battery life or is the same concept being applied where the regulator is dropping the voltage to the P7 (To reduce current) and turning that extra voltage into heat? I'm wondering if thats the case and I will have the same battery life irregardless of using hi/med/low modes b/c any extra voltage gets wasted as heat. Thanks for any replies.

The excess voltage is turned into heat. Lower levels will have longer runtimes than higher levels the curent is lower. e.g. a 2.5A curent high will thoeoreticaly be 1 hour with a 2500mAh battery. A 250ma curent low will be 10 hours with the same battery.

The regulator will drop extra voltage as heat, but if using a LiIon battery the extra voltage is very low and the efficiency might be just as good as a buck/boost driver.
The lower modes are done with pwm, i.e. turning the light off/on in a fast cycle (More than 100 times each second) Keeping the led on 50% of the time will give half brightness. When I do a review I usual record this cycle, it will look like the curve below, the curve shows the brightness measured with a fast light sensor, the first curve shows a medium brightness mode (light in on in about 10% of the time):



The scale is in micro seconds (1/1000000 parts of a second).

Here is a high brightness setting, this drive can not turn on in 100% of the time, only 91% percent:



Both curves are from my Volere AA review


The power draw will follow the pwm percentage, i.e. a 50% pwm will use about 50% current of a 100% pwm. But some current must be added to power the microprocessor, it uses full power in 100% of the time.

HKJ said:

The regulator will drop extra voltage as heat, but if using a LiIon battery the extra voltage is very low and the efficiency might be just as good as a buck/boost driver.
The lower modes are done with pwm, i.e. turning the light off/on in a fast cycle (More than 100 times each second) Keeping the led on 50% of the time will give half brightness. When I do a review I usual record this cycle, it will look like the curve below, the curve shows the brightness measured with a fast light sensor, the first curve shows a medium brightness mode (light in on in about 10% of the time):

The scale is in micro seconds (1/1000000 parts of a second).

Here is a high brightness setting, this drive can not turn on in 100% of the time, only 91% percent:

Both curves are from my Volere AA review


The power draw will follow the pwm percentage, i.e. a 50% pwm will use about 50% current of a 100% pwm. But some current must be added to power the microprocessor, it uses full power in 100% of the time.

Click to expand...

Ahh, I think I understand now. First a resistor must drop any extra voltage down to the level the linear regulator operates at. This is shed as heat and wasted. Once that voltage is regulated into a stable lower voltage going into the driver, the driver uses PWM to acheive the lower light modes. I did not know this driver would do that, I thought it was using aditional resistors to achieve even lower voltages to the LED, and therefore not affording me any extra runtime on the batteries due to more resisors wasting voltage as heat. Thank you!

One more question; When my battery voltage drops down to ~2.8V; the lower limits of this driver, will the PWM adjust the LED to be on proportionally more often to make up for the lower voltage vs when its being driven with fresh batteries at ~3.6V? Not on the brightest mode where full voltage is needed, but lets say durring the low brightness mode? Below 2.8V will the PWM shut down and the driver pretty much go into direct drive?

Eddie-M said:

Ahh, I think I understand now. First a resistor must drop any extra voltage down to the level the linear regulator operates at. This is shed as heat and wasted.

Click to expand...

The regulator is the "resistor", that is electronically adjusted to the correct drive current. On the circuit you linked to there are 8 regulators, each supplying 320mA and a microprocessor that generates the pwm and handles the mode changing.

Eddie-M said:

One more question; When my battery voltage drops down to ~2.8V; the lower limits of this driver, will the PWM adjust the LED to be on proportionally more often to make up for the lower voltage vs when its being driven with fresh batteries at ~3.6V? Not on the brightest mode where full voltage is needed, but lets say durring the low brightness mode? Below 2.8V will the PWM shut down and the driver pretty much go into direct drive?

Click to expand...

This depends on the programming in the microprocessor that controls the pwm, but, to date, I have not seen it done.

HKJ said:

The regulator is the "resistor", that is electronically adjusted to the correct drive current. On the circuit you linked to there are 8 regulators, each supplying 320mA and a microprocessor that generates the pwm and handles the mode changing.

Click to expand...

OK, that makes perfect sense. Thanks for clearing that up for me!

HKJ said:

This depends on the programming in the microprocessor that controls the pwm, but, to date, I have not seen it done.

Click to expand...

So as my battery voltage drains, should I expect each of the three brightness modes to "not be as bright" because the PWM ratio's will stay the same but the voltage going to the LED will just be getting lower as the batteries drain?

Or should I expect the bright level to get dimmer until it is the same intensity as the medium, and then as battery voltage drops, eventually the bright and medium will be the same intensity as the low setting, and with the voltage dropping past that, they will all become dimmer like moonlight? This assuming the microprossesor doesn't cut out and something else all together happens.

Sorry for the repeated questions, but this is helping alot. I can't figure this stuff out with the search function or anything! Thats for the replys!

Eddie-M said:

So as my battery voltage drains, should I expect each of the three brightness modes to "not be as bright" because the PWM ratio's will stay the same but the voltage going to the LED will just be getting lower as the batteries drain?

Click to expand...

Exactly, but first when the battery voltage is below Vf of the led. As long as the battery voltage is above Vf, the regulator will keep constant brightness.

And Vf is not correct, the regulator needs Vf+0.12 volt from the battery to work.

HKJ said:

Exactly, but first when the battery voltage is below Vf of the led. As long as the battery voltage is above Vf, the regulator will keep constant brightness.

And Vf is not correct, the regulator needs Vf+0.12 volt from the battery to work.

Click to expand...

Thank you so much for the help!