ELECTRONIC DEVICES. Assist. prof. Laura-Nicoleta IVANCIU, Ph.D. C3 DR switching circuits

Transcription

1 ELECTRONIC DEVICES Assist. prof. Laura-Nicoleta IVANCIU, Ph.D. C3 DR switching circuits

2 Previously on ED (C2): Constant voltage drop model v D < 0.7 V v D > 0.7 V D (off) D (on) Exponential model i I D S e v D nv T v D < 0.7 V i D = 0 v D i D > 0 = 0.7 V 2

3 Contents Two-port DR networks. DR switching circuits. Voltage transfer characteristic (VTC) Two-port DR networks analysis Applications of two-port DR networks Half-wave rectifier Pulses selector Voltage limiter Maximum multi-port networks Minimum multi-port networks Full wave rectifier diode bridge 3

4 Two-port DR networks. DR switching circuits. Two-port network = circuit w/ two ports input, output Two-port DR network = DR circuit w/ two ports input, output Switching two-port DR network = DR circuit w/ two ports, D (on), (off) The analysis of switching two-port DR networks works with the constant voltage drop model of the diode. 4

5 Voltage transfer characteristic Voltage transfer characteristic (VTC) graphical illustration of v O (v I ) Steps for deducing the VTC: Take into account all possible situations that result from the combination of diode states (on, off) For each situation, Plot the VTC. draw the equivalent circuit find v O determine the range of v I 5

6 Two-port DR networks analysis Example Deduce and plot VTC v O (v I ) Step 1. Write down KVL and Ohm s law for the circuit (circuit s equations) Step 2. Draw the equivalent circuits for D-(on) and D-(off) Step 3. Find v O and the range for v I by replacing the diode s equations in the circuit s equations. Step 4. Write down the complete expression of VTC v O (v I ) and plot it, for D-(on) and D-(off). 6

7 Two-port DR networks analysis Example Deduce and plot VTC v O (v I ) Step 1. Write down KVL and Ohm s law for the circuit (circuit s equations) v + v + v = 0 v O I = i D D R! Always valid, regardless of the state of the diode! O 7

8 Two-port DR networks analysis Example Deduce and plot VTC v O (v I ) Step 2. Draw the equivalent circuits for D-(on) and D-(off) D (off) D (on) 8

9 Two-port DR networks analysis Example Deduce and plot VTC v O (v I ) v + vd + vo = 0 v i R O I = D D (off) Step 3. Find v O and the range for v I by replacing the diode s equations in the circuit s equations. v { D id < 0.7V = 0A v v O D v I = i R = 0 = v D I v 0 < 0.7 O v I v O = 0 v < 0.7 v I v < 0. 7 D O < 0.7V 9

10 Two-port DR networks analysis Example Deduce and plot VTC v O (v I ) v + vd + vo = 0 v i R O I = D D (on) Step 3. Find v O and the range for v I by replacing the diode s equations in the circuit s equations. v { D = 0.7V i D > 0A v I v = O 0 v O = v I 0.7 i D = v I vo R 0.7 > 0 v O R > 0 v O v I > 0 > 0.7V 10

11 Two-port DR networks analysis Example Deduce and plot VTC v O (v I ) Step 4. Write down the complete expression of VTC v O (v I ) and plot it, for D-(on) and D-(off). v O = 0, vi v I 0.7V, < 0.7V v I > 0.7V slope = 1 Application: Voltage rectifier 11

12 Two-port DR networks analysis Example v O = vi 0, v I 0.7V, < 0.7V v I > 0.7V Waveforms slope = 1 output voltage [V] input voltage [V] 2 0.7V 0-2 t 2 1.3V 0-2 t 12

13 Two-port DR networks analysis Influence of V Th and V D,on 0.5 v I [V] v O [V] t Waveforms t t If the input voltage is large enough (>> 0.7 V) V Th can be considered 0 V V D,on can be neglected, meaning that for D (on), v O = v I 0-50 t 13

14 Two-port DR networks analysis Example i D v D a) How does the output voltage look like if the input is a sine wave, 3 V amplitude and 2 V offset? b) What is the peak forward current through diode for R = 2 kω? c) What is the peak reverse voltage v DR across D (v DR =- v D )? d) Repeat a) and b) if the offset of the input voltage becomes -4 V. e) Repeat the above points, assuming the diode is reversed in the circuit. 14

15 Two-port DR networks analysis Other series connections Reverse the diode Change the places of D and R (output voltage collected from D)!Forbidden connection! Never connect a voltage source so that during normal operation, the source can be short-circuited. 15

16 Two-port DR networks analysis Loaded two-port networks What are the effects of R L on the VTC and on the output voltage? 16

17 Applications of two-port DR networks Half-wave rectifier 17

18 Applications of two-port DR networks Pulses selector 18

19 Applications of two-port DR networks Voltage limiters (clamp networks) Reverse engineering: Use the waveforms to deduce and plot VTC v O (v I ). simple double 19

20 Applications of two-port DR networks Maximum multi-port networks v v v v v v A A B B A B > > > > < < v B 0.7V v A 0.7V 0.7V 0.7V D1 ( on), D2 ( off ); v O = va D ( off ), D2 ( on); 1 v O = vb D1 ( off ), D2 ( off ); vo = 0 0.7V 0.7V v O = max( va 0.7V; vb 0.7V; 0V) 20

21 Applications of two-port DR networks Maximum multi-port networks v O = max(v A 0.7 V; v B 0.7 V; 0) v O = max(v A ; v B ; 0) neglecting 0.7 V What is the peak value of the current through each circuit element if R=5 kω? What is the range of values for R, if the peak forward current through each diode is 200 ma? 21

22 Applications of two-port DR networks Minimum multi-port networks v O = min(v A V; v B V; V PS ) v O = min(v A ; v B ; V PS ) neglecting 0.7 V Plot v O (t). 22

23 Applications of two-port DR networks Full-wave rectifier diode bridge ~ - + ~ neglecting 0.7 V positive half, v I >0 D 1, D 3 (on) D 2, D 4 (off) negative half, v I <0 D 1, D 3 (off) D 2, D 4 (on) 23

24 Applications of two-port DR networks Full-wave rectifier center-tapped transformer neglecting 0.7 V 24

25 Applications of two-port DR networks Back-up supply from a 9 V battery V PS = max(8.3v;11.3v) 25

26 Applications of two-port DR networks Example v I ( t) = Vˆ I sinωt v I For the circuit in the figure, R L =50Ω. Assume Vˆ I = 7V. a) Plot v O (t) and i O (t) b) Compute the values of the maximum reverse voltage v DR across each c) diode and the maximum forward current through each diode. Repeat a) and b) assuming Vˆ I = 100V. 26

27 Summary Although the war is not over, today we won the battle against: Two-port DR networks. DR switching circuits. Voltage transfer characteristic (VTC) Two-port DR networks analysis Applications of two-port DR networks Next week: DC switching circuits. DRC rectifiers. Zener diodes. LEDs. To do: Homework 1 27