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oman00339	#1 09/12/2007 - 04h55 Top
Class : Apprenti Posts : 5 Registered on : 09/12/2007 Off line	Hi, I have a quick question... Does anyone know a good ONLINE shop to get an E24 91 Ohm 5% resistor? Here is a picture:
tristan68	#2 09/12/2007 - 15h14 Top
Class : Electronicien en chef Posts : 651 Registered on : 10/07/2007 Off line	Hello oman00339 Resistors are the most common components. You can find them almost everywhere. If you only search for resistors, there's no need to order them on internet, just try to find an electronics shop near your home, they must have them. If you cant find exactly the value you seek, ask for the next value in the series (ie, if you can't find a 100ohms , ask for a 120 ohms). This way , you always go towards safety. cya Edited by tristan68 on 09/12/2007 at 15h17.
Olli	#3 09/12/2007 - 18h27 Top
Class : Apprenti Posts : 1 Registered on : 19/10/2007 Off line	I have another questions about the resistors: I want to build the 3 Point Clip, with the SFH485P LEDs. I have a 4.5V power supply, so in theory i would not need a resistor ('cause the Voltage Drop Accros the three leds is 4.5V) To limit the current of the LEDs, is a 0,1 W 1R Resistor enough? Edited by Olli on 09/12/2007 at 18h56.
Deimos	#4 09/12/2007 - 23h29 Top
Class : Beta Tester Posts : 120 Registered on : 07/11/2007 Off line	that's not exactly true - the LEDs won't simply work in this setup, since the voltage drop across leds equal or greater than to supply voltage means that that the voltage measured across the leds will be zero -> no curent will flow trough them, so there'll be nothing left to limit and the LEDs will not glow, of course. If you use such low supply voltage, you'll probably need to connect the LEDs in paralell, not in serial.
tristan68	#5 09/12/2007 - 23h32 Top
Class : Electronicien en chef Posts : 651 Registered on : 10/07/2007 Off line	Hello Olli You can't use this setup, because if you don't have enough voltage at your resistor, it can't be used as a good current limiter. With a low resistor value, you can experience big current variations for small voltage variations. With the infos you gave, the following setup works fine , and is more battery life friendly than a simple parallel setup : using a 43 ohms resistor as R1 and a 22ohms resistor as R2, you'll get about 70mA in each led. cya

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