I need a help to design a circuits and to do this. 1. An 18V, 50W zener diode is to be used to maintain a constant DC voltage across a load which varies from 10-100ohms. The input voltages is 90V. 2. An unregulated supply varies between 20 and 25V. A 10V zener diode is to regulate this voltage for use in a tape recorder. The recorder draws 30mA when recording and 50mA when playing back. The zener can dissipate a maximum power of 80mW.