The TL431 is a three-terminal programmable shunt regulator that implements Zener-like references with low temperature coefficients. Its output can be programmed from the internally set reference of ...

Nerd Ralph loves cheap and dirty hacks, and for that we applaud him. His latest endeavor is a LiFePO4 battery charger that he made out of parts he had on hand for under $0.50 US. (Although we think… ...

Inside the TL431, [Ken] discovers that transistors aren’t made up of the three layer NPN or PNP sandwich we’ve come to know and love. In fact, the base isn’t even in the middle.

Since the TL431 imposes 2.5 V across R low, then with a 1 mA current imposed by R upp, R low becomes 2.5 V/1 mA = 2.5 kΩ. Then, R upp simply equals 12 V- 2.5 V/1 mA = 9.5 kΩ.