Hello,

I'm working on a project that uses long strips of LEDs with 12V batteries. The LED strips already have the resistors to be powered directly from a 12V source.

I'm faced with 2 problems, which have the same solution. The first is the LEDs are too bright. And the second is that the batteries only last 30 minutes.

I believe if there was some way to create a pwm controller for the LED strips, it would alleviate both problems.

Unfortunately I have a limited budget and 5 of these setups so I would need to have 5 separate PWM controller.

I'd rather not have to make 5 very complex circuits. Is there a simple way to incorporate a transistor and a pot with few other components to essentially create a dimmer? It doesn't have to be the best or most efficient circuit, as long as it's more efficient than adding a simple resistor.

Thank you.

 

I have simulated a simple current regulator PWM circuit for LEDs that uses an LM339 comparator, a MOSFET, an inductor, and a few other parts.
Unfortunately it's on my computer at home and I'm on vacation, so I won't be able to access it until later this week.
If you still need a design I'll get back with you then.

Do you know how much current the strings take?

 

Hello,

Have a look at SgtWookies simple PWM:
http://forum.allaboutcircuits.com/threads/project-simple-pwm-circuit.9016/

Bertus

 

See

 

Same as above but from a different perspective:
http://www.instructables.com/id/Simple-and-dirty-Pulse-Width-Modulation-PWM-Wi/

 

For a meaningful response you need to tell us what these led strips are. How much current do they need? Do they have any internal parts like a resistor or such? What voltage are they designed to run off?

 

For best efficiency you need an inductor in the PWM circuit. Otherwise the efficiency is the same as increasing the resistance in the circuit.

 

A couple of $$'s a crack on ebay.
http://www.ebay.com/itm/PWM-Dimmer-...020177?hash=item51de2fb7d1:g:-IAAAOSwL7VWifZo
Max.

 

If you have five of them, a good solution would be to use a microcontroller.

 

Thanks for all your help everyone.

Unfortunately, I'm a bit lazy and I think that PWM controller that MaxHeadRoom listed would work.

What would happen if I wired in a capacitor in parallel with the output signal? Would that effectively keep a more constant voltage rather than strictly on/off?

 

Actually, I believe it'd be easier to find a switching regulator capable of bringing the 12V down to about 9V.

Would the the voltage output of this one be somewhat smooth? >>>>> http://www.ebay.com/itm/DC-DC-Adjus...065930?hash=item1c67d487ca:g:4WMAAOSwVcFXOcxe

Or would the LED see the pulses with that one too?

 

Would that effectively keep a more constant voltage rather than strictly on/off?

It sounds like you want pwm without knowing why you wanted it.

 

Unfortunately I only have hobby grade electronics experience, but not professional training or experience with these kind of circuits. I come from a mechanical engineering background and have basics physics knowledge of electrical components but not enough circuitry knowledge.

I know why I want PWM, however the LEDs will be viewed by cameras and the flickering is visible on camera. The PWM was supposed to resolve the issue of high brightness and short battery run times, however it seems to cause a problem with flickering.

I need a switching voltage regulator that has a filtered smooth output voltage. Is the one I linked going to provide that kind of performance or will the output still be pulsating?

 

For maximum efficiency you would use a switching current (not voltage) regulator, such as this, and remove any resistance in series with the LEDs (including any internal resistance to the LED strings.
Typical switching regulators switch at frequencies above 20kHz with only a small ripple current, which should be imperceptible to a camera.

 

Check here for PWM with chip 555 controller.

http://www.instructables.com/id/Very-simple-PWM-with-555Modulate-every-thing/