Ingenious chap required

PeeSeeBee

Joined Jun 17, 2011
56
The problem with the other LED lighting up, is due to the 741 not being able to output a rail-to-rail voltage. I'm not sure if rail-to-rail op amps are manufactured in non-smd packages anymore.

I have put your LED configuration into the simulator. Using series resistors of 470Ω, there is only 9mA through the LEDs. Decreasing the resistors to 220Ω increases the current to around 20mA.

http://www.falstad.com/circuit/#%24+1+0.0020+2.5790339917193066+52+12.0+43%0Aa+272+224+400+224+0+10.0+2.0+1000000.0%0Ar+144+144+144+208+0+220.0%0AR+464+80+528+80+0+0+40.0+12.0+0.0+0.0+0.5%0AR+464+384+528+384+0+0+40.0+0.0+0.0+0.0+0.5%0Ax+289+201+297+205+0+15+2%0Ax+292+260+300+264+0+15+3%0Ax+364+214+372+218+0+15+6%0Ax+343+259+351+263+0+15+4%0Ax+343+199+351+203+0+15+7%0Ac+144+80+144+144+0+6.8E-5+3.5720759683499637E-11%0Ar+400+304+272+304+0+10000.0%0Aw+400+224+400+304+0%0Aw+272+304+272+240+0%0Ar+272+304+272+384+0+20000.0%0Ar+464+288+464+384+0+220.0%0Aw+336+240+336+384+0%0Aw+272+80+464+80+0%0Aw+272+384+464+384+0%0Aw+208+80+272+80+0%0Aw+208+208+272+208+0%0As+144+208+144+384+0+1+true%0Aw+144+208+208+208+0%0Aw+272+384+144+384+0%0Ar+464+160+464+80+0+220.0%0Aw+336+208+336+80+0%0Ar+272+240+272+80+0+20000.0%0Ar+208+208+208+80+0+150000.0%0Aw+208+80+144+80+0%0Ap+208+208+208+224+0%0Ap+272+240+256+240+0%0Ap+400+224+400+208+0%0Aw+400+224+416+224+0%0Aw+416+224+416+160+0%0Aw+416+224+416+288+0%0A162+416+160+464+160+1+2.1024259+0.0+1.0+0.0%0A162+464+288+416+288+1+2.1024259+1.0+0.0+0.0%0Aw+464+160+464+288+0%0Ao+28+64+0+34+20.0+9.765625E-5+0+-1%0Ao+29+64+0+34+10.0+9.765625E-5+0+-1%0Ao+30+64+0+34+5.0+9.765625E-5+0+-1%0A

Another solution is to keep the original LED configuration & add a series diode (or 2) to each LED. A rectifier diode such as 1N4001/2/3 etc. or even a signal diode, such as a 1N914/1N4148 should do. To compensate for the extra volt drop, the series resistors were reduduced to 390Ω.

http://www.falstad.com/circuit/#$+1...25E-5+0+-1 o+29+64+0+34+5.0+9.765625E-5+0+-1
 
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