Buck regulator

Discussion in 'The Projects Forum' started by jmoffat64@verizon.net, Jan 13, 2012.

  1. jmoffat64@verizon.net

    Thread Starter New Member

    Dec 26, 2011
    I recently replaced the bulb in my 14.4 volt work light with a 3 watt led. I needed to reduce the voltage to 9v so I used a 3 terminal regulator. It works like a charm but the regulator gets wicked hot inside the handle. Another concern is the waste of energy. The ideal solution would be to use the same regulator as the heart of a buck regulator. The space in the handle is limited so the circuit needs to be simple. I need help with the circuit. Maybe someone can point me in the right direction.
  2. jimkeith

    Active Member

    Oct 26, 2011
  3. bountyhunter

    Well-Known Member

    Sep 7, 2009
    Since VIN and the load are basically fixed: A cheap and easy way to do it would be to use a free running 555 timer for a signal to run the switch transistor and just adjust the pulse width to get about 50% (which will give you around 6V) and then use a power resistor in series with the LED to set the current. You would not need to regulate the voltage.

    You did not say what current the LED needs for your app. I assume the voltage is about 4V?
  4. bertus


    Apr 5, 2008

    Leds are current driven componets and not voltage driven.
    Most 3 Watt leds I know are 700 mA and about 4 Volts.
    You need to make a current regulator for the Led to make it work.


    PS Don't use your email-adresses as user name.
  5. jmoffat64@verizon.net

    Thread Starter New Member

    Dec 26, 2011
    Wow I posted this thing so long ago I forgot about it. I was actually shocked when I saw my email address as my user name. Wow is that a colossal blunder! I will address that right away.

    Thanks for the great replies. All well taken.

    Something I neglected to mention is that the LED Bulb I used is a drop in replacement for a regular flashlight bulb. Specs listed as 3.5v to 9v and 140 to 750 ma. There must be some electronic wizardry built into the bulb. My bad for not giving that info up front.

    What I did was to buy a 3 terminal switching regulator designed as a drop in replacement for the 7805. The setup works well. Battery life is great. I haven't tried it yet but I'm sure I could leave it turned on for a week. Brightness is almost as good as the 10w halogen bulb I replaced plus the bulb doesn't fail when the flashlight is dropped.

    Now what is the best way to change my username?