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Step 4.015E (a) Refer to Figure E4. 15 in the text book for the diode circuit to be designed. It consists of string of four diodes. Draw the small signal equivalent circuit. R rd rd rd rd - Figure Step 7 The diode is replaced by resistance, rd As the load current is zero, the change in output voltage is equal to the change in diode voltage, and the change in load current is equal to change in diode current, diD Determine the total diode resistance (resistance of the combination of four diodes in series), 4rd which is the change in output voltage to the change in current. Substitute 20 mV for dvD and mA for diD 20 20 Step of 7 Determine the diode current, ID Here, Thermal voltage VT is 25 Substitute 25 mV for and for rd 5 The string of four diodes should provide an output voltage of =3 V at no load. Determine the nominal value of the current in the diode string, ID 15-3 12 R Substitute 5 mA for in the equation. R 12 Thus, the value of resistance, Ris Step of 7 (b) Write the formula for the saturation For output voltage, =3 V voltage drop across each diode is, 3 V 4 Step Substitute mA for iD for and 25 mV for in the formula of saturation current. 0.75 A Thus, the saturation current of the diodes is Step (c) Determine the diode current with load. Substitute 5 mA for and mA for in the equation. Write the formula for voltage across each diode. Substitute V for A for and A for in the equation. =0.74431 V Determine the voltage drop across four diodes which is equal to times each diode voltage as the diodes are connected in series 4VD =2.97723 V Thus, the output voltage with a load current of mA is 2.99723 V. Step The output voltage at no-load is Determine the change in output voltage from no load to load. V = mV Thus, the change in output voltage at load current of mA to no- load -22.77