Jump to content
Electronics-Lab.com Community

Can you put a dimmer on LEDs?


Recommended Posts

An LED is a diode with a fairly constant voltage across it, not a resistive hot piece of wire like a light bulb.
LEDs operate with current, not voltage. A supply voltage higher than the LED voltage is used and the current is limited with a current limiting resistor in series with them. The lower the resistance then the higher the current and brightness.
A potentiometer to limit the current wastes a lot of power and might over-heat the potentiometer. Duty-cycle control by pulse-width-modulation is frequently used to dim LEDs efficiently (without much wasted heat). A high current is pulsed through the LED at a frequency high enough so that you don't see flickering and the duty-cycle of each cycle's on time vs its off time changes the brightness. ;D

Link to comment
Share on other sites

It would be a fairly uncommon circuit to generate heat at this point with a standard LED. Any circuit which normally uses a resistor as a current limit to the LED can use a pot to adjust the brightness. Don't forget to use a resistor in series with the pot, because the pot will allow zero resistance at one end. This has no more effect on this circuit than changing the resistor to a different value for the same purpose. Just remember to calculate the current min and max and use correct ratings of resistor and pot (you do know the formula for calculating LED resistor, right?) 

From a manufacturing point of view, it would be a waste of components and board space to make a pwm circuit to adjust the brightness of a panel light.

MP

Link to comment
Share on other sites

In this case I think PWM is the best solution as using a current limiting resistor or power transistor might require an large expensive heatsink - it depends on the LED current, voltage drop and power supply voltage.

How much current does you LED require?

What's the forward voltage drop?

What power supply are you using?

Or:
Does the LED have a built in current limiting circuit? Do you just connect it up to the power supply and it works?

Link to comment
Share on other sites

You may laugh audioguru, but some LEDs (I'm talking more about LED lamps/modules than discrete LEDs here) have a built-in resistor or constant current regulator - some modules even have built in switching regulators. ;D

If the LED is like this then you might be able to get away with using a normal PWM circuit even if it uses a built-in switcher it might still work but you'd better make the PWM frequency a small fraction of the switcher's or it won't work properly.

Link to comment
Share on other sites


Yes I do know the calculations and I'm using the LEDs to light the interior of my boat (not panel light) and I'm not using a curcuit board of any kind.


Does not sound like you want to use a pot, then. You need to look at the spec sheet for the LEDs you are using.  If you do not want to build a PWM controller or circuit on a board to control this, you might be able to get by with a car headlight dimmer. You might get more useful ideas than this if you could draw your schematic and let everyone know the part numbers of the LEDs. There is a lot of electronic experience here at your fingertips. You should post your diagram.

MP
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Loading...
 Share

×
  • Create New...