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ok, I certainly don't get that current when I break the connection to the TL431 in either schem........if I short out the TL431, I get no led current, and if I open the TL431, I get about 70mA led current.What are Q3 and Q4 in LINREG 1_TL431REG designed to do? As shown it seems that if TL431 fails then Q4 turns on, Q3 turns off and the current through D2,D7 rises to ~470mA
Depends where you break the connection. Try disconnecting R7.I certainly don't get that current when I break the connection to the TL431
I did that, and I get 64mA in one string, and 54mA in the otherdisconnecting R7
Indeed. Why turn off all the LEDs just because one has failed? I don't see the logic in that.if one of the leds from the 2_string fails open, then Q4 turns off, and Q3 turns on and turns off all the leds........that's what its supposed to do.....admittedly its a bit of a strange type of protection circuitry
... if you run both sims for different temperatures (I tried 10C to 50C) you'll find (surprisingly?) that the LED current varies less with temperature when the 431 is used without the closed loop feedback.Please could you advise on why the designer did not use an TL431 to provide closed loop negative feedback