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For this circuit I have to find the V_out/V_in ratio and my problem lies on one instance and that is ,

if V1 is negative (for the case V1< Diode on Voltage) all the current flows through the diode and diode acts like constant voltage source which in turn causes some current flow through R_1. My question is ,Why Diode On voltage is the only cause for the current flow through R_1 ? Does V_1 not have any role on causing current flow through R_1 since V1 is in magnitude greater than Diode_On voltage?

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My question is ,Why Diode On voltage is the only cause for the current flow through R_1 ?

If you are modeling the forward conduction of the diode as a constant voltage then there is also a constant voltage across R1. With a constant voltage across R1, due to ohm's law the current through R1 is constant.

Does V_1 not have any role on causing current flow through R_1 since V1 is in magnitude greater than Diode_On voltage?

All V1 does when it alters is change the current through D1 but, while ever the voltage is constant across the diode (forward conduction) the current through R1 is fixed by the diode forward voltage.

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  • \$\begingroup\$ so if i use ideal model then there will be no current through R2? \$\endgroup\$ Dec 5 '20 at 19:08
  • \$\begingroup\$ Well, it’s hard to prove of course but yes, correct. \$\endgroup\$
    – Andy aka
    Dec 5 '20 at 20:07

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