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Subject: Re: Pulsing LED/High Current - Simple Circuit Question
Date: Wed, 8 Jan 2003 23:21:26 -0800
Organization: Nextra UK
NNTP-Posting-Date: Wed, 8 Jan 2003 23:21:25 +0000 (UTC)
X-Newsreader: Microsoft Outlook Express 4.72.3110.1
David A. Johnson wrote in message ...
>Mark Klinger wrote in message
>> Thanks very much for all the helpful responses regarding pulsing LEDs
>> and their apparent brightness. I'd like the run the fundamentals of
>> my circuit by everyone to make sure my thinking is correct.
>> Currently, at DC, my LED has Vf of 1.7V and max current of 100mA.
>> Since my supply is 13.8V, would it be correct that:
>> 13.8V-1.7V-0.2V (Sat. of Transistor)/.1A = 120ohm resistor?
>> Since I am able to pulse the LED at 2A with a very short pulse
>> duration, would I then change to a 6 ohm resistor since:
>> 13.8-1.7V-0.2V/2A = 5.95 ohm?
>> This 2A is peak current I believe, which means that the short duration
>> pulses (<1mS) should be significantly "brighter" than the DC 20mA
>> intensity, correct?
>> Thanks again everyone for helping me understand this.
>If you are planning on using the LED as a visible light flasher, with
>a slow flash rate, then you should set the pulse at about 3
>milliseconds, instead of 1ms. Anything shorter than 3ms will appear
>to be less bright. Anything longer will be wasted power. The human
>eye responds well to flash durations around 2 to 5 milliseconds.
Do you have any references to support these 'optimum' flash times?
Is Blundell-Rey invalid?
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