ok i am using a buck regulator to power an led from a 12v battrey the regulator is based on the LM2596S is it posable to introduce a pwm sig to dim the led

 

If the need for PWM is to dim the LED, then yes dimming is (probably) possible by adjusting the feedback.

Please post your current circuit, showing telling how the LED is connected so people can further advise you.

 

Hi this is the regulator i am using and the led is connected to the output the led has a fv of 7.4volts and can take up to 1.2amp and yes if its possable i would like to dim it using pwm

http://i.ebayimg.com/t/5x-DC-DC-Buck-Converter-Adjustable-Step-Down-Module-LM2596-Power-Supply-1-5-35v-/00/s/NTAwWDUwMA==/$(KGrHqF,!h0FBIBtytiZBQfOlfEdK!~~60_35.JPG

 

Hi this is the regulator i am using and the led is connected to the output the led has a fv of 7.4volts and can take up to 1.2amp and yes if its possable i would like to dim it using pwm

http://i.ebayimg.com/t/5x-DC-DC-Buck-Converter-Adjustable-Step-Down-Module-LM2596-Power-Supply-1-5-35v-/00/s/NTAwWDUwMA==/$(KGrHqF,!h0FBIBtytiZBQfOlfEdK!~~60_35.JPG

Post your schematic not a link to the part on ebay. Anyone can easily search for the datasheet so that link is pretty much useless.

The LM2596 is a voltage regulator. Not a current regulator. Unless you have some kind of current limiting you LEDs aren't going to last very long. The LM2673 does have current limiting btw but it is 3A and might be more than you need. You can check the datasheet.

 

The URL you pasted in is not complete, but it looks like you are planning to buy one of those pre-build LM2596 power supply modules. If the module allows you to vary the voltage output of the module, you can use the method the manufacturer specified to vary the voltage and then put a resistor (which you should probably have anyway) in sereis with the LED.

As Spinniker points out, it would really be better to drive the LED from an LED power module, which sets or senses the LED's current and adjusts the input accordingly. This kind of power supply has been discussed several discussed many times on this forum, so I recommend a search of the forum to see a variety of circuits that do what you want.

 

Just buy/build with any of the hundreds of LED driver IC's out there that have built in PWM input pin for dimming. That way you get a true constant current supply and simple pwm dimming.