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Can we use this PWM LED driver circuit to save battery power?

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Willen

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-I will change its duty cycle to adjust its appropriate brightness.
-It has 19KHz frequency, I don't know how much is suitable. Audioguru was saying that a LED swithing less than 30mS will start dim light. If we turn the LED on 30mS and turn it off in other remaining time then we get same high brightness but but from less current drain (turning OFF the LED maximum time). So worrid about output frequency.

-I hope on resistance of the darlington will give series resistance for the LED. Analysis needed.

I can post .asc for LTspice too.
Regards
 

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What you are doing does change the "brightness" but it does not save power.
Well that depends on what you call save power.
example: 10mA 100% of the time>>your 555 circuit >>10mA 50% of the time uses 1/2 the power but is 1/2 as bright.
example:4V at 5mA >>PWM>>2V at 10mA. (using a real PWM with a inductor and diode) (4 volt supply and 2 volt LED)
 
Felt little confussion :)

In the case of 100mA LED?

There are hundreds of circuits in internet which are complicated too. For why they use such complicated thing and why not just they use a single limiting resistor?
 
The most simple is to use the right resistor. It is not easy to adjust the brightness.

In some applications we want to adjust the brightness from 0 to 100% with a simple adjustment. This can be done with duty cycle. (something like what you posted)

In some applications we are trying to save power. If the battery is 12 volts and the LED is 3 volts then the resistor has 9 volts across it. This way 9/12 of the power is in the resistor. Using a "buck converter" 3 volts at 100mA can come from 12 volts at 25mA. This uses many parts including a inductor.
 
Willen, your circuit is missing an important current-limiting resistor in series with the LED and is also missing an important supply bypass capacitor.

A Li-Ion battery cell is 4.2V when fully charged then its voltage drops slowly as it discharges until its voltage is 3.0V to 3.2V when the load MUST be disconnected.

Modern cars use LEDs for the brake lights. When simply driving the lights are dimmed with PWM and you can see them flickering. When the lights are activated by the brakes to be very bright then the pulse width is maximum so the LEDs get full continuous DC without flickering.

A blink of an LED for a duration of 30ms or longer appears as bright as a constant duration. A blink with a duration less than 30ms appears to be dimmed even though the current is the same.
But the duration of each of your 19kHz pulses are for only 0.053ms maximum so it is the duty-cycle that determines the brightness of your LED. When the pulses have equal on and off times then the LED is turned on for half the time and appears to have half the current of an LED lit with continuous DC.

You will notice that your vision's sensitivity to brightness is logarithmic. Half the current in an LED appears to be dimmed only a little, and not appear to be half as bright.
 
Hi AG, I am in confuse-- your chaser circuits are tourch lights for night OR flasher (blinking) for intertainment?
 
I have LED lights all over the place in my home and yard.
I have 27 solar garden lights in my yard (almost half of them were given away for free by my electrical utility company). I have replaced most of the LEDs and batteries that rusted away.
I have 6 chasers each with a different LED color, all side-by-side on a shelf pointing at the entrance of my family room that they are in.

The Chasers have 10 LEDs in a circle mounted on a Compact Disc (CD). Each LED blinks for about 30ms then the next LED blinks. The LEDs blink one-at-a-time and chase around and around 3 or 4 times then there is a pause with no LED blinking. The pause duration is for about 2 seconds then the chasing begins again. They blink day and night because they do not have a light sensor.
They use 74HC high speed Cmos logic ICs that still work when the battery voltage drops to 2V and the average current is fairly low since the LEDs are turned off for most of the time so the AA alkaline battery cells last for months. Each battery cell in a 3V chaser (it uses two cells) drops to 0.7V when its LEDs are appear to be dimmed. Each battery cell in a 6V chaser (it uses four cells) drops to 0.9V when its LEDs are appear to be dimmed.
 

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