Electronics- Zener Diodes and Photodiodesdenethor.wlu.ca/pc320/lectures/zenbeam.pdf ·...

DiodesZener diodesPhotodiodes

Optical Isolation

ElectronicsZener Diodes and Photodiodes

Terry Sturtevant

Wilfrid Laurier University

September 26, 2017

Terry Sturtevant Electronics Zener Diodes and Photodiodes


Optical Isolation

Basic Diode OperationApplication: Clamping

Basic Diode Operation

forward bias



Optical Isolation


Basic Diode Operation

reverse bias



Optical Isolation


The diode will conduct when it is forward biased when theinput voltage goes above about 0.7V .

The diode will not conduct when it is reverse biased until theinput voltage goes above about the reverse breakdownvoltage, which is typically large.



Optical Isolation


The diode will conduct when it is forward biased when theinput voltage goes above about 0.7V .The diode will not conduct when it is reverse biased until theinput voltage goes above about the reverse breakdownvoltage, which is typically large.



Optical Isolation


Application: Clamping

It may sometimes be necessary to ensure that a signal doesnot become negative.For instance, a sensor inside the engine of a car may pick upelectrical noise. A negative voltage due to noise could destroya microprocessor.To avoid this, the signal may be clamped so that it nevergoes below zero.This can be done using a diode.



Optical Isolation



It may sometimes be necessary to ensure that a signal doesnot become negative.

For instance, a sensor inside the engine of a car may pick upelectrical noise. A negative voltage due to noise could destroya microprocessor.To avoid this, the signal may be clamped so that it nevergoes below zero.This can be done using a diode.



Optical Isolation



It may sometimes be necessary to ensure that a signal doesnot become negative.For instance, a sensor inside the engine of a car may pick upelectrical noise. A negative voltage due to noise could destroya microprocessor.

To avoid this, the signal may be clamped so that it nevergoes below zero.This can be done using a diode.



Optical Isolation



It may sometimes be necessary to ensure that a signal doesnot become negative.For instance, a sensor inside the engine of a car may pick upelectrical noise. A negative voltage due to noise could destroya microprocessor.To avoid this, the signal may be clamped so that it nevergoes below zero.

This can be done using a diode.



Optical Isolation



It may sometimes be necessary to ensure that a signal doesnot become negative.For instance, a sensor inside the engine of a car may pick upelectrical noise. A negative voltage due to noise could destroya microprocessor.To avoid this, the signal may be clamped so that it nevergoes below zero.This can be done using a diode.



Optical Isolation


Clamping a signal



Optical Isolation


Vi

Rd

Vo



Optical Isolation


The diode will conduct once it is forward biased.

The output voltage will follow the input until the input goesbelow about −0.7V .From then on the output will not decrease.(This slight negative voltage will not be a problem for mostelectronics.)The resistor should be chosen so that the maximum currentthrough the diode is within the specified limits.



Optical Isolation


The diode will conduct once it is forward biased.The output voltage will follow the input until the input goesbelow about −0.7V .

From then on the output will not decrease.(This slight negative voltage will not be a problem for mostelectronics.)The resistor should be chosen so that the maximum currentthrough the diode is within the specified limits.



Optical Isolation


The diode will conduct once it is forward biased.The output voltage will follow the input until the input goesbelow about −0.7V .From then on the output will not decrease.

(This slight negative voltage will not be a problem for mostelectronics.)The resistor should be chosen so that the maximum currentthrough the diode is within the specified limits.



Optical Isolation


The diode will conduct once it is forward biased.The output voltage will follow the input until the input goesbelow about −0.7V .From then on the output will not decrease.(This slight negative voltage will not be a problem for mostelectronics.)

The resistor should be chosen so that the maximum currentthrough the diode is within the specified limits.



Optical Isolation


The diode will conduct once it is forward biased.The output voltage will follow the input until the input goesbelow about −0.7V .From then on the output will not decrease.(This slight negative voltage will not be a problem for mostelectronics.)The resistor should be chosen so that the maximum currentthrough the diode is within the specified limits.



Optical Isolation

Application: ClippingCalculating Resistance

Zener diodes

The Zener diode will conduct in reverse bias once the voltageexceeds the Zener voltage, VZ .The output voltage will follow the input until the inputexceeds VZ .From then on the output will not increase.It is usually placed in a voltage divider with a resistor chosenso that the maximum current through the diode is within thespecified limits.



Optical Isolation


Zener diodes

The Zener diode will conduct in reverse bias once the voltageexceeds the Zener voltage, VZ .

The output voltage will follow the input until the inputexceeds VZ .From then on the output will not increase.It is usually placed in a voltage divider with a resistor chosenso that the maximum current through the diode is within thespecified limits.



Optical Isolation


Zener diodes

The Zener diode will conduct in reverse bias once the voltageexceeds the Zener voltage, VZ .The output voltage will follow the input until the inputexceeds VZ .

From then on the output will not increase.It is usually placed in a voltage divider with a resistor chosenso that the maximum current through the diode is within thespecified limits.



Optical Isolation


Zener diodes

The Zener diode will conduct in reverse bias once the voltageexceeds the Zener voltage, VZ .The output voltage will follow the input until the inputexceeds VZ .From then on the output will not increase.

It is usually placed in a voltage divider with a resistor chosenso that the maximum current through the diode is within thespecified limits.



Optical Isolation


Zener diodes

The Zener diode will conduct in reverse bias once the voltageexceeds the Zener voltage, VZ .The output voltage will follow the input until the inputexceeds VZ .From then on the output will not increase.It is usually placed in a voltage divider with a resistor chosenso that the maximum current through the diode is within thespecified limits.



Optical Isolation


reverse bias



Optical Isolation


reverse bias

VZ



Optical Isolation


Vi

RzVo

Here’s the typical circuit.



Optical Isolation


Here’s a Zener diode circuit simulation drawing.



Optical Isolation




Optical Isolation


Vin



Optical Isolation


Vin Vout



Optical Isolation


Vin Vout

For a 10V Zener diode, the output voltage range is much less thanthe input range.



Optical Isolation


Vin Vout



Optical Isolation


Vin Vout

The output range is smaller if the input range is smaller.



Optical Isolation


Application: Clipping

Often it’s necessary to ensure that a signal does not exceed acertain voltage in order to avoid harming circuitry whichfollows.Again, using the car sensor example, a sensor inside theengine of a car may pick up electrical noise of hundreds ofvolts occasionally which could destroy a microprocessor.To avoid this, the signal may be clipped so that it never goesabove a fixed voltage.This can be done using a Zener diode.



Optical Isolation



Often it’s necessary to ensure that a signal does not exceed acertain voltage in order to avoid harming circuitry whichfollows.

Again, using the car sensor example, a sensor inside theengine of a car may pick up electrical noise of hundreds ofvolts occasionally which could destroy a microprocessor.To avoid this, the signal may be clipped so that it never goesabove a fixed voltage.This can be done using a Zener diode.



Optical Isolation



Often it’s necessary to ensure that a signal does not exceed acertain voltage in order to avoid harming circuitry whichfollows.Again, using the car sensor example, a sensor inside theengine of a car may pick up electrical noise of hundreds ofvolts occasionally which could destroy a microprocessor.

To avoid this, the signal may be clipped so that it never goesabove a fixed voltage.This can be done using a Zener diode.



Optical Isolation



Often it’s necessary to ensure that a signal does not exceed acertain voltage in order to avoid harming circuitry whichfollows.Again, using the car sensor example, a sensor inside theengine of a car may pick up electrical noise of hundreds ofvolts occasionally which could destroy a microprocessor.To avoid this, the signal may be clipped so that it never goesabove a fixed voltage.

This can be done using a Zener diode.



Optical Isolation



Often it’s necessary to ensure that a signal does not exceed acertain voltage in order to avoid harming circuitry whichfollows.Again, using the car sensor example, a sensor inside theengine of a car may pick up electrical noise of hundreds ofvolts occasionally which could destroy a microprocessor.To avoid this, the signal may be clipped so that it never goesabove a fixed voltage.This can be done using a Zener diode.



Optical Isolation


Clipping a signal



Optical Isolation


Vi

RzVo



Optical Isolation


Calculating Resistance

Three parameters are needed to calculate the requiredresistance for a Zener diode:

1 supply voltage, VS2 Zener voltage, VZ3 recommended Zener current, I

The ideal value for the resistance, R, is given by:

R = VS − VZI



Optical Isolation




1 supply voltage, VS

2 Zener voltage, VZ3 recommended Zener current, I


R = VS − VZI



Optical Isolation




1 supply voltage, VS2 Zener voltage, VZ

3 recommended Zener current, IThe ideal value for the resistance, R, is given by:

R = VS − VZI



Optical Isolation




1 supply voltage, VS2 Zener voltage, VZ3 recommended Zener current, I


R = VS − VZI



Optical IsolationCalculating Resistance

Photodiodes

Photodiodes are diodes which operate differently whenexposed to light.They can operate in two modes:

1 forward-biased; a.k.a. photovoltaic mode2 reverse-biased; a.k.a. photocurrent mode

LEDs can also be used as photodiodes.




Photodiodes

Photodiodes are diodes which operate differently whenexposed to light.

They can operate in two modes:1 forward-biased; a.k.a. photovoltaic mode2 reverse-biased; a.k.a. photocurrent mode





Photodiodes







Photodiodes


1 forward-biased; a.k.a. photovoltaic mode

2 reverse-biased; a.k.a. photocurrent modeLEDs can also be used as photodiodes.




Photodiodes







Photodiode symbol




photocurrentmode

photovoltaicmode

dark




photocurrentmode

photovoltaicmode

increasing light




To use a photodiode in photovoltaic mode:

Measure the forward-biased voltage which changes with lightTo use a photodiode in photocurrent mode:Put it reverse-biased in a voltage divider like a Zener diodeand measure the reverse-biased voltage which changes withlight




To use a photodiode in photovoltaic mode:Measure the forward-biased voltage which changes with light

To use a photodiode in photocurrent mode:Put it reverse-biased in a voltage divider like a Zener diodeand measure the reverse-biased voltage which changes withlight




To use a photodiode in photovoltaic mode:Measure the forward-biased voltage which changes with lightTo use a photodiode in photocurrent mode:

Put it reverse-biased in a voltage divider like a Zener diodeand measure the reverse-biased voltage which changes withlight




To use a photodiode in photovoltaic mode:Measure the forward-biased voltage which changes with lightTo use a photodiode in photocurrent mode:Put it reverse-biased in a voltage divider like a Zener diodeand measure the reverse-biased voltage which changes withlight





Three parameters are needed to calculate the requiredresistance for a photodiode:

1 supply voltage, VS2 photocurrent, Ip3 desired voltage change with light, Vo


R = VS − VoIp






1 supply voltage, VS

2 photocurrent, Ip3 desired voltage change with light, Vo


R = VS − VoIp






1 supply voltage, VS2 photocurrent, Ip

3 desired voltage change with light, Vo


R = VS − VoIp






1 supply voltage, VS2 photocurrent, Ip3 desired voltage change with light, Vo


R = VS − VoIp



Optical Isolation

Optical Isolation

Optical isolation using an LED and a phototransistor orphotodiode

can transmit DC (i.e. steady-state values)only one waycannot transmit powerthe above two conditions mean that there is no danger ofvoltage spikes as there is with inductive isolation



Optical Isolation

Optical Isolation


can transmit DC (i.e. steady-state values)

only one waycannot transmit powerthe above two conditions mean that there is no danger ofvoltage spikes as there is with inductive isolation



Optical Isolation

Optical Isolation


can transmit DC (i.e. steady-state values)only one way

cannot transmit powerthe above two conditions mean that there is no danger ofvoltage spikes as there is with inductive isolation



Optical Isolation

Optical Isolation


can transmit DC (i.e. steady-state values)only one waycannot transmit power

the above two conditions mean that there is no danger ofvoltage spikes as there is with inductive isolation



Optical Isolation

Optical Isolation


can transmit DC (i.e. steady-state values)only one waycannot transmit powerthe above two conditions mean that there is no danger ofvoltage spikes as there is with inductive isolation



Optical Isolation

The resistors are used because effectively the LED and thephototransistor are current devices, and usually signals areprocessed as voltages.

The values chosen for the resistors should be consistent withthe current specifications for the device.The amount of DC isolation provided by an optoisolator isusually in the range of kV.At some point the insulation will break down and arcs canoccur.



Optical Isolation

The resistors are used because effectively the LED and thephototransistor are current devices, and usually signals areprocessed as voltages.The values chosen for the resistors should be consistent withthe current specifications for the device.

The amount of DC isolation provided by an optoisolator isusually in the range of kV.At some point the insulation will break down and arcs canoccur.



Optical Isolation

The resistors are used because effectively the LED and thephototransistor are current devices, and usually signals areprocessed as voltages.The values chosen for the resistors should be consistent withthe current specifications for the device.The amount of DC isolation provided by an optoisolator isusually in the range of kV.

At some point the insulation will break down and arcs canoccur.



Optical Isolation

The resistors are used because effectively the LED and thephototransistor are current devices, and usually signals areprocessed as voltages.The values chosen for the resistors should be consistent withthe current specifications for the device.The amount of DC isolation provided by an optoisolator isusually in the range of kV.At some point the insulation will break down and arcs canoccur.



Optical Isolation

VsVi

Vo

Ri

Ro



Optical Isolation

Whenever sensors are in a place where it is possible for highvoltages to be induced, optical isolation should be used to protectelectronic devices which follow.


Electronics- Zener Diodes and Photodiodesdenethor.wlu.ca/pc320/lectures/zenbeam.pdf ·...

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