electronic devices. dr switching circuits.pdf · laura-nicoleta ivanciu, electronic devices 15 c3...

ELECTRONIC DEVICESAssist. prof. Laura-Nicoleta IVANCIU, Ph.D.

C3 – DR switching circuits

2Laura-Nicoleta IVANCIU, Electronic devices

vD < 0.7 V iD = 0

D – (off) D – (on)

vD < 0.7 V vD > 0.7 V

vD = 0.7 V iD > 0


T

D

nVv

SD eIi ≅

Constant voltage drop model

Exponential model

Previously on ED (C2):



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


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 theconstant voltage drop model of the diode.



Voltage transfer characteristic

Voltage transfer characteristic (VTC)

graphical illustration of vO (vI)


Steps for deducing the VTC: Take into account all possible situations that result from the

combination of diode states (on, off) For each situation,

draw the equivalent circuitfind vOdetermine the range of vI

Plot the VTC.


Two-port DR networks analysis

Deduce and plot VTC vO (vI)


Step 1. Write down KVL and Ohm’s law for the circuit (circuit’s equations)

Example

Step 2. Draw the equivalent circuits for D-(on) and D-(off)Step 3. Find vO and the range for vI by replacing the diode’s equations in the circuit’s equations. Step 4. Write down the complete expression of VTC vO (vI) and plot it, for D-(on) and D-(off).


Two-port DR networks analysis



Step 1. Write down KVL and Ohm’s law for the circuit (circuit’s equations)

Example

Rivvvv

DO

ODI

==++− 0

! Always valid, regardless of the state of the diode!


Two-port DR networks analysisC3 – DR switching circuits

Step 2. Draw the equivalent circuits for D-(on) and D-(off)

Example

D – (off) D – (on)




Step 3. Find vO and the range for vIby replacing the diode’s equations in the circuit’s equations.

Example

D – (off)


Rivvvv

DO

ODI

==++− 0

0=Ov

OID vvv −=

V7.0<Iv

0== Riv DO

7.0<Dv 7.0<− OI vv

7.00 <−Iv

V7.0<DvA0=Di{



Step 3. Find vO and the range for vIby replacing the diode’s equations in the circuit’s equations.

Example

D – (on)


Rivvvv

DO

ODI

==++− 0

{ A0>Di

V7.0=Dv

07.0 =++− OI vv

Rvi O

D =

V7.0>Iv

7.0−= IO vv

0>Ov

07.0 >−Iv

0>RvO



Step 4. Write down the complete expression of VTC vO (vI) and plot it, for D-(on) and D-(off).

Example


slope = 1

Application:

Voltage rectifier=OvV7.0<Iv

V,7.0−Iv V7.0>Iv

,0



Example

slope = 1

Waveforms

=OvV7.0<Iv

V,7.0−Iv V7.0>Iv

,0

-2

0

2

inpu

t vol

tage

[V]

t

-2

0

2ou

tput

vol

tage

[V]

t

1.3V

0.7V



Influence of VTh and VD,on

Waveforms

-50

0

50

t

-0.5

0

0.5

t

vI [V]

vO [V]

-2

-1

0

1

2

t

-10

-5

0

5

10

t

If the input voltage is large enough (>> 0.7 V) VTh can be considered 0 V VD,on can be neglected, meaning that for D – (on), vO = vI



Example iD

vD

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 vDR across D (vDR=- vD)?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.



Other series connections

Reverse the diode

Change the places of D and R (output voltage collected from D)

Never connect a voltage source so that during normal operation, the source can be short-circuited.

!Forbidden connection!



Loaded two-port networks

What are the effects of RL on the VTC and on the output voltage?


Applications of two-port DR networks

Half-wave rectifier




Pulses selector




Voltage limiters (clamp networks)

simple

double

Reverse engineering: Use the waveforms to deduce and plot VTC vO (vI).




Maximum multi-port networks

>>

V7.0A

BA

vvv

V7.0);(),( 21 −=−− BO vvonDoffD

0);(),( 21 =−− OvoffDoffD

)V0;V7.0;V7.0max( −−= BAO vvv

V7.0);(),( 21 −=−− AO vvoffDonD

>>

V7.0B

AB

vvv

<<

V7.0V7.0

B

A

vv




Maximum multi-port networks

vO= max(vA – 0.7 V; vB – 0.7 V; 0)

vO= max(vA; vB; 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?




Minimum multi-port networks

vO= min(vA+ 0.7 V; vB+ 0.7 V; VPS)

vO= min(vA; vB; VPS) neglecting 0.7 V

Plot vO(t).




Back-up supply from a 9 V battery

)V3.11;V3.8max(=PSV



SummaryAlthough 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: Full-wave DR rectifiers. DC switching circuits. DRC rectifiers. LEDs.

To do: Homework 1


electronic devices. dr switching circuits.pdf · laura-nicoleta ivanciu, electronic devices 15 c3...

Documents