Probably a stupid question, but I'm not sure so I have to ask
I have 15 LEDs (TSAL6400 TR Diode @ 100 mA) in parallel, divided into 2 groups. First group is 4 LEDs, second group is 11 LEDs. The first group is always on, the second group can be switched on and off by a switch. Wiring is all done, no problems there.
The problem is my power source. Previously, I used a special device that allowed me to send exactly 100 mA through the entire system, so no resistors were needed. Now, I can no longer access that device so I need to use a 9V battery (the square one). This also means that I have to use resistors now.
I read somewhere that it is necessary for parallel circuits to use a different resistor for EACH LED (is this correct?). I also read that for parallel circuits Req = 1/R1 + 1/R2 ... 1/Rn but I'm not sure how to interpret this.
By doing R = U / I I find that R = 90 Ω. Does this mean that I need to give every LED a 90 Ω resistor, or do I have to devide 90 by 15? If so, wouldn't that give problems with my switch? Because if the switch is off, only 4 LEDs are powered so I would have to divide 90 by 4 instead of 15..
I have 15 LEDs (TSAL6400 TR Diode @ 100 mA) in parallel, divided into 2 groups. First group is 4 LEDs, second group is 11 LEDs. The first group is always on, the second group can be switched on and off by a switch. Wiring is all done, no problems there.
The problem is my power source. Previously, I used a special device that allowed me to send exactly 100 mA through the entire system, so no resistors were needed. Now, I can no longer access that device so I need to use a 9V battery (the square one). This also means that I have to use resistors now.
I read somewhere that it is necessary for parallel circuits to use a different resistor for EACH LED (is this correct?). I also read that for parallel circuits Req = 1/R1 + 1/R2 ... 1/Rn but I'm not sure how to interpret this.
By doing R = U / I I find that R = 90 Ω. Does this mean that I need to give every LED a 90 Ω resistor, or do I have to devide 90 by 15? If so, wouldn't that give problems with my switch? Because if the switch is off, only 4 LEDs are powered so I would have to divide 90 by 4 instead of 15..