I need a resistor with a costant current adapter ?

[FAQ-Forum-Bot]

Hi, I'm Bruno from Torino-Italy, I'm buying 9 Cree XR-E 7090 royal blue and i want to power them in a serial connection with your costant current supply 700 ma IP20. The XR-E 7090 at 700ma need 3,5V, My question is : I need a resistor to connect ((9*3,5)+1) the 9 leds to the IP20 ?

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[schlosshund]

Hello Bruno,

that is not possible. The constant current supply is only for a maximum of 8 leds. Nine leds will not work. Just read the technical informations for the constant current supply.

I would prefer this constant current supply, but you need two of them: one time for 4 leds one time for 5 leds for example:
http://www.leds.de/LED-Zubehoer/Strom-u ... m=art%204e

You don´t need any additional resistor. All will work direct with the constant current supply.

[Ronald90]

I assume you would like to use this constant current supply: http://www.leds.de/LED-Zubehoer/Strom-u ... -IP20.html

In this case the previously made statement is incorrect! If putting all LEDs in a row the voltage you need is added up, the constant current supply can give at most 36V, if i divide these by 9 i get 4V which the LED might have max. to still be working at 700mA. Since these LEDs will very likely have a voltage of less than 4V at a current of 700mA the power supply should easily be able to supply 9 LEDs of this kind. What is correct is: You must not use a resistor!