wiring led display

[vampyre308]

Hi all, first post here, and I have a few questions. I am attempting to make a LED array to custom light a scale model project. I need to run 11 LEDs off of a 12v source, so I was thinking of running them in series parallel, with four separate legs to the circuit. The first leg will have 4 red LEDs (2v 30mA) and a 150Ω resistor, second leg - 3 blue LEDs (3.6v 30mA) 47Ω resistor, third leg - 2 white LEDs (3.6v 30mA) 180Ω resistor, fourth and final leg - 3 LEDs (3.6v 30mA) with a 47Ω resistor. All resistors are 1/4w, P/S is 12v (8 AA battery) . So my question is will this work? And if so should there be a current regulator in the circuit to maintain a steady 30 mA? If yes will one regulator be ok for it or should each leg have it's own?

Thanks for any help or feedback. It has been about 20 years since I played with trons, and as the saying goes, if you don't use it you loose it. I have forgotten more than I remember

 

[Diver300]

The resistors will control the current.

If you use a current regulator, you have to have one in each leg, and that would give a current that varies less than if you use resistors.

The voltage from the 8 AA batteries will fall as they run down, so the relative brightness of the different colours might vary if you don't have a current regulator in each leg.

 

[audioguru]

Nobody makes a "3.6V" LED. The LED has a range of maybe from 3.2V to 3.6V. You get whatever they have when you buy them.
If the blue and white LEDs are all 3.2V then the 47 ohm current-limiting resistor value is too low and the LEDs might burn out with a current of 51mA.

Design using "worst case" specs to guarantee that everything will work properly.

 

[vampyre308]

Thanks for the feedback, I really do appreciate it. The specs on the LEDS is forward voltage of 3.2-3.8 withMax Peak Forward Current 75mA , so I settled on 3.6 for an estimate until they arrive from mail order. Any ideas on the current regulator for each leg? Is there any IC that could be used for this application?

 

[audioguru]

Maximum allowed peak forward current is for only a moment, not continuously like you will be doing.
Its maximum allowed continuous current is probably 30mA and you should operate them at no more than 25mA.

An LM3914, LM3915 or LM3916 bar graph IC has 10 outputs with regulated currents. There are some Oriental bar graph ICs with fewer outputs but I don't know where to buy them.

 

[vampyre308]

Ok very cool, Thanks Audio for the info. Now some quick recalculations, and research into those ICs and how to put them into the circuit and I will pretty much set.... I hope