Maker Factory ELECTRONICS EXPERIMENTS BOX Manual page 327

Circuit 208: The functioning principle is described on page 299.
Circuit 209 to 211: The level of Zener voltage is monitored at the base of T2. T1 will reduce current, if voltage
drops. The voltage drop via R2 decreases, the Zener voltage rises to its original value. The reverse process
takes place, when the Zener voltage increases.
Fig. 3.209: Circuit 209 – Active Zener
diode 4V
Fig. 3.208: Circuit
208 – NAND gate
with LED
329