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

C3 – DR switching circuits

T

D

nVv

SD eIi ≅

Constant voltage drop model

Exponential model

Previously on ED (C2):

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C3 – DR switching circuits

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

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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.

C3 – DR switching circuits

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Voltage transfer characteristic

Voltage transfer characteristic (VTC)

graphical illustration of vO (vI)

C3 – DR switching circuits

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.

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Two-port DR networks analysis

Deduce and plot VTC vO (vI)

C3 – DR switching circuits

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).

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Two-port DR networks analysis

Deduce and plot VTC vO (vI)

C3 – DR switching circuits

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!

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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)

Deduce and plot VTC vO (vI)

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Two-port DR networks analysisC3 – DR switching circuits

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

Example

D – (off)

Deduce and plot VTC vO (vI)

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{

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Two-port DR networks analysisC3 – DR switching circuits

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

Example

D – (on)

Deduce and plot VTC vO (vI)

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

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Two-port DR networks analysisC3 – DR switching circuits

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

Example

Deduce and plot VTC vO (vI)

slope = 1

Application:

Voltage rectifier=OvV7.0<Iv

V,7.0−Iv V7.0>Iv

,0

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Two-port DR networks analysisC3 – DR switching circuits

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

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Two-port DR networks analysisC3 – DR switching circuits

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

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Two-port DR networks analysisC3 – DR switching circuits

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.

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Two-port DR networks analysisC3 – DR switching circuits

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!

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Two-port DR networks analysisC3 – DR switching circuits

Loaded two-port networks

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

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Applications of two-port DR networks

Half-wave rectifier

C3 – DR switching circuits

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Applications of two-port DR networks

Pulses selector

C3 – DR switching circuits

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Applications of two-port DR networks

Voltage limiters (clamp networks)

simple

double

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

C3 – DR switching circuits

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Applications of two-port DR networks

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

C3 – DR switching circuits

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Applications of two-port DR networks

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?

C3 – DR switching circuits

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Applications of two-port DR networks

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).

C3 – DR switching circuits

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Applications of two-port DR networks

Back-up supply from a 9 V battery

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

C3 – DR switching circuits

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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

C3 – DR switching circuits