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Say i had a 12v 10a regulated voltage source, from a sla hooked up to a picoups charger/regulator.

I want to drive ~72w of leds (max watts, its a pwm controller), basically my strip lighting that is powered from a 12v 6a WW.

How would you go about regulating the current down to that with the highest effeciency?

What about 12v 700ma 10w led's? or 20w 12v led's in 10x2 parallel (or series if i get a boost converter)?

Basically, whats the most effecient way to current limit, but not constant current these led's from a 12v 10a max regulated source?

I just want to take that 12v source, and pwm it through some kind of dc-dc converter that limits current if possible with an external pwm rf dimmer inline before the converter. Either that, or a cheap driver that could be pwm'd with an arduino.
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SMPS generally doesn't like a dynamic load so putting a pwm control on an led powered by a smps is not an easy task.

If you have to stay with your existing power supply, try to put a mosfet switch to the led string, and they by-pass the whole thing with a small load, to provide some passage for the current. You can switch the mosfet to provide some pwm control for the led.

Otherwise, look to a regular dc/dc converter with external switches for your application.
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Say i had a 12v 10a regulated voltage source, from a sla hooked up to a picoups charger/regulator.
How would you regulate 12V SLA to 12V??  SLA 12V battery will provide from over 13V fully charged down to 11V when low, you can't get a regulated 12V passively.  picoups? do you have a link for that?
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I want to drive ~72w of leds (max watts, its a pwm controller), basically my strip lighting that is powered from a 12v 6a WW.
WW?  Please describe things completely and with links if possible.  What's the LED strip too, come to that?
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How would you go about regulating the current down to that with the highest effeciency?
Normally a 12V LED strip has own current-limiting resistors, there is no concept of regulating the current, you provide 12V.
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What about 12v 700ma 10w led's? or 20w 12v led's in 10x2 parallel (or series if i get a boost converter)?
So what about them?  Any datasheets?  - note that boost converters and PWM aren't a great combination, boost converters don't switch on/off very fast.
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Basically, whats the most effecient way to current limit, but not constant current these led's from a 12v 10a max regulated source?
Either you use LED modules that desire a constant voltage, in which case it will draw the right current, OR you need to provide constant current drive (perhaps via current limiting resistor and constant voltage though).
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I just want to take that 12v source, and pwm it through some kind of dc-dc converter that limits current if possible with an external pwm rf dimmer inline before the converter. Either that, or a cheap driver that could be pwm'd with an arduino.

Still trying to understand exactly what you mean, so correct me if I'm wrong:

You have 12V LED strips, a 12V 10A power supply.  You want to PWM the LEDs.

If that's the case you add lots of decoupling to the supply and a beefy MOSFET (with driver chip) to switch the LEDs.  So long as the supply can provide enough current for the maximum load, there's no issue with current.
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