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diodes

# diodes - EE 323 Winter 2009 Diode Approximations in Circuit...

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EE 323 Winter 2009 Diode Approximations in Circuit Applications January 14, 2009 In many applications, we can represent diodes as a series combination of a switch and a bat- tery as shown in Fig. 1. Under normal oper- ating (nonbreakdown) conditions, a measurable current can only flow in the forward direction through the diode, so the normal conducting state of the diode is commonly called the forward bias state or on state and the nonconducting state is commonly called the reverse bias state or off state . In the forward bias state, i D > 0 and v D V ON = 0 . 7 V. In the reverse bias state, i D 0 and v D < V ON = 0 . 7 V. v D + _ v ON i D + _ i D v D Figure 1: Left: diode circuit symbol. Right: cir- cuit model representing the diode as a switch and a battery. Typical value of V ON = 0 . 7 V. When an application circuit contains other- wise linear elements and a single diode, the state of the diode can be determined by a straight- forward process of elimination. For example, we can assume a diode is in the conducting state with the switch in closed position and the bat- tery engaged, then analyze the circuit to verify that the current flows in the correct direction for forward bias conditions. If we find in analysis that the current flows through the diode in the opposite direction, we conclude that the diode must be in the reverse bias state. To check, we repeat the analysis of the circuit with the switch

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