EE40 Lecture 26 Venkat Anantharam 4 04 08 Reading Chap 10 Diodes EE40 Spring 2008 Slide 1 Venkat Anantharam Load Line Analysis Method 1 Graph the I V relationships for the non linear element and for the rest of the circuit 2 The operating point of the circuit is found from the intersection of these two curves I RThev I VThev VThev RThev operating point V V VThev The I V characteristic of all of the circuit except the non linear element is called the load line EE40 Spring 2008 Slide 2 Venkat Anantharam Ideal Diode Model of PN Diode Circuit symbol ID I V characteristic ID A VD Switch model ID VD forward bias reverse bias VD V An ideal diode passes current only in one direction An ideal diode has the following properties when ID 0 VD 0 when VD 0 ID 0 EE40 Spring 2008 Diode behaves like a switch closed in forward bias mode open in reverse bias mode Slide 3 Venkat Anantharam Large Signal Diode Model Circuit symbol ID I V characteristic ID A VD Switch model ID forward bias reverse bias VDon VD V VDon VD For a Si pn diode VDon 0 7 V RULE 1 When ID 0 VD VDon RULE 2 When VD VDon ID 0 EE40 Spring 2008 Slide 4 Diode behaves like a voltage source in series with a switch closed in forward bias mode open in reverse bias mode Venkat Anantharam Diode Large Signal Model Use piece wise linear model EE40 Spring 2008 Slide 5 Venkat Anantharam How to Analyze Circuits with Diodes A diode has only two states forward biased ID 0 VD 0 V or 0 7 V reverse biased ID 0 VD 0 V or 0 7 V Procedure 1 Guess the state s of the diode s 2 Check to see if KCL and KVL are obeyed 3 If KCL and KVL are not obeyed refine your guess 4 Repeat steps 1 3 until KCL and KVL are obeyed Example If vs t 0 V diode is forward biased else KVL is disobeyed try it vs t EE40 Spring 2008 vR t If vs t 0 V diode is reverse biased else KVL is disobeyed try it Slide 6 Venkat Anantharam Diode Logic AND Gate Diodes can be used to perform logic functions AND gate Inputs A and B vary between 0 Volts low and Vcc high Between what voltage levels does C vary when the diode requires a nonzero forward bias voltage to turn on output voltage is high only if both A and B are high Vcc RAND VOUT 5 A C EOC B Slope 1 Shift 0 7V Up 0 0 EE40 Spring 2008 Slide 7 5 VIN Venkat Anantharam
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