A 6.8 V Zener diode specified at 5 mA to have Vz = 6.8 V and rz = 20 II with /zi = 0.2 mA, is operated in a regulator circuit using a 200 f2 resistor and a 9 V supply. Estimate the knee voltage of the Zener. For no load, what is the lowest supply voltage for which the Zener remains in breakdown opera-tion? For the nominal supply voltage, what is the maximum load current for which the Zener remains in breakdown operation? For half this load current, what is the lowest supply voltage for breakdown opera-tion?