Really stupid question about led wiring

[LinkZ]

Hi guys, sorry for the stupid question, but I want to wire a couple of leds in the following mixed series-parallel scheme:



Assuming each led is 3V 5mA, i will have 6V 15mA current in total, right? The "advantage" of this scheme SHOULD be that i need only a single resistor. However I don't know if there are disadvantages about this wiring scheme. Let me know and sorry for the ridiculous question.

[jeroen79]

There is no guarantee that the current will divide evenly over the parallel LEDs.
With three series of LED-LED-resistor it will.

[DmitryL]

Hi guys, sorry for the stupid question, but I want to wire a couple of leds in the following mixed series-parallel scheme:
Assuming each led is 3V 5mA, i will have 6V 15mA current in total, right? The "advantage" of this scheme SHOULD be that i need only a single resistor. However I don't know if there are disadvantages about this wiring scheme. Let me know and sorry for the ridiculous question.

If LEDs that you connect in parallel come from the same wafer, then you can assume that they have identical parameters and can be paralleled without much harm. You can see this approach in "LED clusters" that are usually sold as "20 Wt LED" etc.
If you pick several LEDs from a box, you can't guarantee that their parameters (like voltage drop vs current and voltage drop vs temperature) are identical and current won't be distributed equially between them. In your case (currents are very small) this would just menan that you may have different brightness for LEDs in parallel.

[TimFox]

In general, for all types of diodes, "equalizing" resistors in series with each diode in a parallel connection are required to ensure at least rough equality of current between the individual diodes.

[SL4P]

I understand what the other replies are saying, but I don't get the circuit...
Is the 7V supply AC - using the half wave characteristic of the diodes?

Perhaps you could redraw the diagram to 'self explain' the intended operation...?

[bills]

check here, will help with LED circuits.
http://led.linear1.org/led.wiz

[Richard Crowley]

Repeating, hard-wiring LEDs in parallel is NOT RECOMMENDED.
Use one of the online LED calculators like the one @bills suggested.