lecture 4 ver2 diode_app

Chapter 2:Diode Applications (cont.)

Prepared by:Ikhwan Hafiz Muhamad

[email protected] 1, E10-C13

Copyright Ikhwan H Muhamad, Universiti Malaysia Pahang © 2010 1

Recap Last Lecture

VVPIV

VV

VV

V

outp

outpAVG

poutp

7.02

2

7.02

)(

)(

(sec))(


VVPIV

VV

VVV

outp

outpAVG

poutp

7.0

2

4.1

)(

)(

(sec))(

(sec)

)(

(sec))( 7.0

p

outpAVG

poutp

VPIV

VV

VVV

HALF-WAVE RECTIFIER CENTER-TAPPED FULLWAVE RECTIFIER

BRIDGE FULL-WAVE RECTIFIER

Diode Applications

1. Half-wave & full-wave rectification2. Power supply filter & regulators3. Clippers & Clampers


Power Supply Filters and Regulators

• Explain and analyze the operation and characteristics of power supply filters and regulators

• Explain the purpose of a filter• Describe the capacitor-input filter• Define ripple voltage & calculate the ripple

factor• Discuss surge current & voltage regulation


Sub-Chapter Outcomes

Power Supply Filters


• Filter is a capacitor in a power supply used to reduce the variation of the output voltage rectifier

ALDifference AC & DC?


Capacitor-Input Filter




Ripple Voltage: the small variation (undesirable) inthe capacitor voltage due to the charging &discharging of the filter capacitor




Full rectifier easier to filter because of the shorter time between peaks (smaller ripple)


DC

ppr

V

Vr )(



Ripple Factor, r, is an indication of filter effectiveness (the lower the ripple factor the better filter)

)(

)()(

2

11

1

rectpL

DC

rectpL

ppr

VCRf

V

VCRf

V




Answer: 0.079 @ 7.9%

Eg. Determine the ripple factor for the filtered bridge rectifier with a load as indicated in figure below


FSM

psurge I

VVR

4.1(sec)


Surge Current

At the instant the switch is closed, voltage is connected to the bridge and the uncharged capacitor appears as a short. Produce ISurge through D1 & D2

ISurge could destroy the diodes

RSurge used to prevent the diodes from destroy. RSurge < RL;

Voltage Regulators

78XX OutputInput from

rectifier


Voltage Regulators Combination of capacitor-

input filter with integrated circuit voltage regulator

Operation:i. the input to the regulator

is first filtered with a capacitor to reduce the ripple to<10%

ii. The regulator reduce the ripple to a negligible amount (acceptable level)

3 terminals: input, output & reference

Voltage Regulators


Percent Regulation – present the performance of a voltage regulator

• Line regulation specify how much change occurs in the output voltage for a given change in input voltage

Line regulation

• Load regulation specify how much change occurs in the output voltage over a certain range of load current values.

Load regulation

%100

IN

OUT

V

V

%100

FL

FLNL

V

VV

1) A certain 7805 regulator has a measured no-load output voltage of 5.18V and a full load output of 5.15V.What is the load regulation expressed as a percentage?

2) If the no-load output voltage of a regulator is 24.8V and the full-load output is 23.9V, what is the load regulation expressed as a percentage?

14

Exercise

Review section

1) When a 60Hz sinusoidal voltage is applied to the input of a half-wave rectifier, what is the output frequency?

2) When a 60Hz sinusoidal voltage is applied to the input of a full-wave rectifier, what is the output frequency?

3) What cause the ripple voltage on the output of a capacitor-input filter?

4) If the load resistance connected to a filtered power supply is decreased, what happens to the ripple voltage?

15

5. A certain rectifier filter produce a dc o/p voltage of 75V with peak-to-peak ripple voltage of 0.5V. Calculate the ripple factor?

6. A certain full-wave rectifier has a peak o/p voltage of 30V. A 50uF capacitor-input filter is connected to the rectifier. Calculate the peak-to-peak ripple and the dc o/p voltage developed across a 600ohm resistance.

7. What is the percentage of ripple for the rectifier in question 6?

16

Diode Applications

1. Half-wave & full-wave rectification2. Power supply filter & regulators3. Clippers & Clampers


Clippers and Clampers

• Explain and analyze the operation of diode limiting & clamping circuits

• Explain the operation of diode limiters• Determine the output voltage of a biased

limiter• Explain the operation of diodes clampers


Sub-Chapter Outcomes

Diode Limiters (Clippers)

• A diode network that have the ability to “clip” (cut short/crop) off portions of signal voltages above or below certain limits, i.e. the circuits limit the range of the output signal.

• Such a circuit may be used to;– protect the input of a CMOS logic gate against

static– eliminate amplitude noise– fabricate new waveforms from an existing

signal


Diode Limiters


• 2 general of clippers:a) Series clippersb) Parallel clippers

• Parallel ClippersDiode in a branch parallel to the load.

• Series ClippersDiode is in series with the load.


Diode Limiters



Parallel Clipper


• Whenever the input is below 0.7V, the diode is reversed biased and appears as an open.

• The output voltage, VOUT looks like the negative part of the input, but with a magnitude determined by the voltage divider formed by R1 and RL, as follows:

• If R1 is small compared to RL, then VOUT=VIN


Parallel Clipper


1. Define the input and output port2. Determine the current flow of the circuit3. Determine the applied voltage (transition

voltage) that will result in a change of state for the diode from the “off” to “on” state

4. Draw the output waveform directly below the applied voltage using the same scales


Analysis Steps for Parallel Clipper

Example

What should you expect to see displayed on an oscilloscope connected across RL in the limiter shown above? Sketch the waveform for 2 cycles.

Noted: +Vp= +10V; R1 = 100 ohm, RL=1kohm, diode model = 1N4001



Parallel Clipper with Biased Limiters

By adding a DC source to the circuit, the voltage required to forward bias the diode can be

changed.



Parallel Clipper with Biased LimitersAL

Matlab

Diode Limiting Circuits - Example

The diode is forward-biased when the output tries to go above +3.0 V. This causes the output to be limited to voltages less than +3.0 V.

What is the output voltage of positive limiter shown? Sketch the waveform

VinRL

R1

0+

–

VBIAS 0

10 V

2.3 V=

1.0 kW

100 kW3.0 V

Vin

Vout

Solution


Eg: Determine the output voltage waveform for the circuit below.


Parallel Clipper with Biased Limiters

Answer: Clipped at ±5.7V

Eg: Solution



Voltage-Divider Bias


Eg: Describe the output voltage waveform for the diode limiter in Figure below.


Voltage-Divider Bias

Answer: Clipped at +8.95V

Eg: Solution

33



Series Clipper

Example : • Determine the Vo and sketch the o/p

waveform for the below network. Assume diode is ideal.

+

V=4 V

RL

Vo

-

+

-

Vit0 T/2 T

Vi

16

-16

VON4ViOFF5ViOFF6ViOFF7ViOFF16

VON3VON2VON1VoDiode stateVi

+

V=4 V

Vo

-

+

-Vi

+

V=4 V

Vo

-

+

-Vi

t0 T/2

Vo16

4

Solution:• + ve region

Solution (continued):• - ve region (always ON state)

VON-4

VON-5

VON-6

VON-7

VON-16

VON-3

VON-2

VON-1VoDiode stateVi

t0 T/2

Vo16

4

TV=4 V

Vo

-

+

-Vi

+

t0 T/2

Vo16

4

T

The resulting o/p waveform

Example : Repeat the previous example using a silicon diode with VD=0.7 V

+

V=4 V

RL

Vo

-

+

-Vi

VD=0.7 V

V

VVVi

VVVi

D

D

3.3

7.04

0

Solution:

Solution (continued): For i/p voltages greater than 3.3 V the diode open cct and Vo=Vi.

For i/p voltages less than 3.3 V the diode short cct and the network result as;

+

V=4 V

RL

Vo

-

+

-Vi

VD=0.7 V

V

Vo

3.3

7.04

t0 T/2

Vo16

3.3

T

The resulting o/p waveform


40

Summary of Series Clippers : Refer

Electronic Devices and Circuit Theory: International Edition, 8th

Edition (Robert L. Boylestad) page 87.

Diode Clampers


• Known as DC-Restorer

• Widely use in analogue television receivers

• A clamper is a network constructed of a diode, resistor, and a capacitor that shifts a waveform to a different dc level without changing the appearance of the applied signal

Diode Clampers


Positive Clamper

Diode Clampers


Negative Clamper

• Note:• RC time constant should be at least ten times the period

of the input frequency.

Diode Clampers


Negative Clamper

Eg: Determine the output voltage waveform. Assume that RC is large enough to prevent significant capacitor discharge

Answer: Vdc = -23.3V

Eg: SolutionAL

Matlab

Sim

ulatio

n

Diode Clampers

46

Summary of clamping circuits : Refer

Electronic Devices and Circuit Theory: International Edition, 8th Edition (Robert L. Boylestad) page 91.

1) What component in a clamping circuit effectively acts as a battery?

2) What is the difference between a +ve limiter and a –ve limiter?

Review section

lecture 4 ver2 diode_app

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universiti malaysia

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