Comments on: Driving an LED with or without a resistor http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/ Alex' blog Wed, 10 Mar 2010 23:29:18 +0100 http://wordpress.org/?v=2.8.6 hourly 1 By: Tobi’s Corner » Blog Archive » USB DotMatrix Display http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/comment-page-1/#comment-95056 Tobi’s Corner » Blog Archive » USB DotMatrix Display Mon, 01 Feb 2010 11:27:33 +0000 http://tinkerlog.com/?p=579#comment-95056 [...] by http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/ I started to build a USB driven display. I ordered some big green 5×7 dotmatrix display from [...] [...] by http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/ I started to build a USB driven display. I ordered some big green 5×7 dotmatrix display from [...]

]]> By: Mike http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/comment-page-1/#comment-89425 Mike Sat, 14 Nov 2009 00:07:42 +0000 http://tinkerlog.com/?p=579#comment-89425 I would think that a current limiting resistor is ALWAYS required, even if Vsource = Vf. One main reason I can think of is the negative temperature coefficient of a Diode. If a Diode heats up, it's internal resistance decreases and thus it will sink more current thus heating the diode even further thus... Thermal Runaway. This leads to high currents and burnt leds! I would think that a current limiting resistor is ALWAYS required, even if Vsource = Vf.

One main reason I can think of is the negative temperature coefficient of a Diode. If a Diode heats up, it’s internal resistance decreases and thus it will sink more current thus heating the diode even further thus… Thermal Runaway.

This leads to high currents and burnt leds!

]]> By: Thorsten http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/comment-page-1/#comment-87843 Thorsten Wed, 21 Oct 2009 14:33:21 +0000 http://tinkerlog.com/?p=579#comment-87843 Hi Steve, as far as I know, all commercial available LED driver ICs are in fact current sources. I also would think that this is the right way to go, since the save limiting factor for the LED is the current not the voltage. And good current sources also have a very high efficiency. But you probably can not reach such high efficiency with the simple one transistor circuits mentioned in the wikipedia article. An additional advantage of such a driver is that you can use it within a wide range of input voltages. greetings Thorsten Hi Steve,
as far as I know, all commercial available LED driver ICs are in fact current sources. I also would think that this is the right way to go, since the save limiting factor for the LED is the current not the voltage. And good current sources also have a very high efficiency. But you probably can not reach such high efficiency with the simple one transistor circuits mentioned in the wikipedia article.
An additional advantage of such a driver is that you can use it within a wide range of input voltages.

greetings

Thorsten

]]> By: Steve http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/comment-page-1/#comment-87725 Steve Tue, 20 Oct 2009 01:13:14 +0000 http://tinkerlog.com/?p=579#comment-87725 "And if the brightness should be constant, I think a current source would be a good choice. http://en.wikipedia.org/wiki/Current_source" A current source does exactly the same thing as a current-limiting resistor, in this application. The load isn't changing, so the current doesn't need to be regulated. It just makes a transistor act as a resistor to limit the current to a preset value. Waste of energy and money. “And if the brightness should be constant, I think a current source would be a good choice. http://en.wikipedia.org/wiki/Current_source”

A current source does exactly the same thing as a current-limiting resistor, in this application. The load isn’t changing, so the current doesn’t need to be regulated. It just makes a transistor act as a resistor to limit the current to a preset value. Waste of energy and money.

]]> By: Electronics-Lab.com Blog » Blog Archive » Driving an LED with or without a resistor http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/comment-page-1/#comment-87713 Electronics-Lab.com Blog » Blog Archive » Driving an LED with or without a resistor Mon, 19 Oct 2009 20:42:18 +0000 http://tinkerlog.com/?p=579#comment-87713 [...] an LED with or without a resistor - [Link] Tags: Led Filed in Led | 1 views No Comments [...] [...] an LED with or without a resistor – [Link] Tags: Led Filed in Led | 1 views No Comments [...]

]]> By: Blinking the leds http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/comment-page-1/#comment-86318 Blinking the leds Mon, 28 Sep 2009 22:03:37 +0000 http://tinkerlog.com/?p=579#comment-86318 [...] I connect a led on PB1 through a 220 ohms resistor. It should limit the current in the led to about 15mA (Explanation). [...] [...] I connect a led on PB1 through a 220 ohms resistor. It should limit the current in the led to about 15mA (Explanation). [...]

]]> By: KentD http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/comment-page-1/#comment-80350 KentD Fri, 26 Jun 2009 12:39:35 +0000 http://tinkerlog.com/?p=579#comment-80350 Another good way to get light instead of warming up a resistor is simply to use LED's in series. I have used 5 red LED's in series on a 9V battery with no resistor. Current was in the normal range. Or, 2 white and 1 red. Whites LED's drop about 3.4V, red drop about 1.6. 3.4 + 3.4 + 1.6 = 8.4V, and that is close to the actual voltage of a 9V battery. One problem I have had is measuring the current; A meter will change the value! So now I attach a CdS photocell to one LED and measure the brightness (as indicated by the resistance of the CdS cell) at the desired current. Then in the circuit I can see if it is brighter, meaning more current. Another good way to get light instead of warming up a resistor is simply to use LED’s in series. I have used 5 red LED’s in series on a 9V battery with no resistor. Current was in the normal range. Or, 2 white and 1 red. Whites LED’s drop about 3.4V, red drop about 1.6. 3.4 + 3.4 + 1.6 = 8.4V, and that is close to the actual voltage of a 9V battery. One problem I have had is measuring the current; A meter will change the value! So now I attach a CdS photocell to one LED and measure the brightness (as indicated by the resistance of the CdS cell) at the desired current. Then in the circuit I can see if it is brighter, meaning more current.

]]> By: Cube follow up « Dave’s Blog http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/comment-page-1/#comment-74963 Cube follow up « Dave’s Blog Thu, 23 Apr 2009 22:41:31 +0000 http://tinkerlog.com/?p=579#comment-74963 [...] LEDs at a higher voltage than their max rating if you reduce the duty cycle as described in this article. Possibly related posts: (automatically generated)Patch 3.1 PTR RoundupIs it really safe to [...] [...] LEDs at a higher voltage than their max rating if you reduce the duty cycle as described in this article. Possibly related posts: (automatically generated)Patch 3.1 PTR RoundupIs it really safe to [...]

]]> By: Alex http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/comment-page-1/#comment-74637 Alex Tue, 21 Apr 2009 09:00:50 +0000 http://tinkerlog.com/?p=579#comment-74637 Hi Lucas, there are many different kind of LEDs out there. Maybe try one of these high power LEDs. And you definitely need a current limitting resistor in that sort of circuit. Even high power LEDs are far from handling 12 V. Cheers, Alex Hi Lucas,
there are many different kind of LEDs out there. Maybe try one of these high power LEDs. And you definitely need a current limitting resistor in that sort of circuit. Even high power LEDs are far from handling 12 V.
Cheers,
Alex

]]> By: Lucas Miranda http://tinkerlog.com/2009/04/05/driving-an-led-with-or-without-a-resistor/comment-page-1/#comment-74590 Lucas Miranda Tue, 21 Apr 2009 01:59:20 +0000 http://tinkerlog.com/?p=579#comment-74590 Im trying to switch my stock fog lights to LED lights, but the LED lights are not as bright as a regular bulb. How can I make it brighter? Is that happening because of some resistor in my car? Thank you Im trying to switch my stock fog lights to LED lights, but the LED lights are not as bright as a regular bulb. How can I make it brighter? Is that happening because of some resistor in my car? Thank you

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