Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems.

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Old January 4th 05, 06:54 AM
Robert Wolcott
 
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Default Testing a photodiode

I have a silicon photodiode and I'm unsure if it is working or not. How
would I go about testing it? Things I have done so far:

Measured the resistance - 50 megs in either orientation, regardless of
lighting condition.
Measured resistance with a 5mw diode laser shining on it.

Anything else I should do? How do these typically fail?

Thanks,
Bob



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Old January 4th 05, 09:55 AM
klasspappa[remove]
 
Posts: n/a
Default

A diod is a diod, not a resistor.
See it as a current source, and put it into a opamp to form a current to
voltage converter...

Robert Wolcott wrote:
I have a silicon photodiode and I'm unsure if it is working or not. How
would I go about testing it? Things I have done so far:

Measured the resistance - 50 megs in either orientation, regardless of
lighting condition.
Measured resistance with a 5mw diode laser shining on it.

Anything else I should do? How do these typically fail?

Thanks,
Bob



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Old January 4th 05, 12:59 PM
Sam Goldwasser
 
Posts: n/a
Default

"klasspappa[remove]" writes:

A diod is a diod, not a resistor.
See it as a current source, and put it into a opamp to form a current
to voltage converter...


Even simpler: Just hook it to a multimeter on mA and shine a light on it.

With your laser diode, the output should be somewhere around 0.2 to 0.5 mA/mW.

For more accuracy, reverse bias it with a few V and measure the current.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

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Robert Wolcott wrote:
I have a silicon photodiode and I'm unsure if it is working or not.
How would I go about testing it? Things I have done so far:
Measured the resistance - 50 megs in either orientation, regardless
of lighting condition.
Measured resistance with a 5mw diode laser shining on it.
Anything else I should do? How do these typically fail?
Thanks,
Bob

  #4   Report Post  
Old January 4th 05, 02:35 PM
Robert Wolcott
 
Posts: n/a
Default

I'll give that a try. This diode is part of a relative power meter on my
yag laser. The meter is currently not working and I'm not sure if it is the
diode or the circuit. The circuit can be seen at:

http://oregonstate.edu/~wolcottr/Yag...0schematic.jpg

Tests I have run include:

Measured the voltage supplied to the diode via BNC connector and it is 5.0
volts
placed a 1k resistor across the BNC connector and the power meter was
pegged.
Hooked up the photodiode to the circuit and shined a 5mw diode laser into it
and there was no reading (direct illumination).

Does this sound about right?

Thanks,
Bob




"Sam Goldwasser" wrote in message
...
"klasspappa[remove]" writes:

A diod is a diod, not a resistor.
See it as a current source, and put it into a opamp to form a current
to voltage converter...


Even simpler: Just hook it to a multimeter on mA and shine a light on it.

With your laser diode, the output should be somewhere around 0.2 to 0.5
mA/mW.

For more accuracy, reverse bias it with a few V and measure the current.

--- sam | Sci.Electronics.Repair FAQ Mirror:
http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ:
http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites:
http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the
excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above
is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.


Robert Wolcott wrote:
I have a silicon photodiode and I'm unsure if it is working or not.
How would I go about testing it? Things I have done so far:
Measured the resistance - 50 megs in either orientation, regardless
of lighting condition.
Measured resistance with a 5mw diode laser shining on it.
Anything else I should do? How do these typically fail?
Thanks,
Bob



  #5   Report Post  
Old January 4th 05, 02:56 PM
Sam Goldwasser
 
Posts: n/a
Default

"Robert Wolcott" writes:

I'll give that a try. This diode is part of a relative power meter on my
yag laser. The meter is currently not working and I'm not sure if it is the
diode or the circuit. The circuit can be seen at:

http://oregonstate.edu/~wolcottr/Yag...0schematic.jpg

Tests I have run include:

Measured the voltage supplied to the diode via BNC connector and it is 5.0
volts


Is the input 5 VDC or 12 VDC? 5 VDC wouldn't peg a 1 mAFS meter since
there is a 10K current limiting resistor.

placed a 1k resistor across the BNC connector and the power meter was
pegged.


Sounds consistent with 12 VDC input and the circuit working properly.

Hooked up the photodiode to the circuit and shined a 5mw diode laser into it
and there was no reading (direct illumination).


Do the tests above but sounds like it's bad.

Does this sound about right?


Yep. You can also test the photodiode on the diode check range of your
DMM. It should test like a silicon diode. I bet it tests open both ways.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.


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Old January 4th 05, 09:16 PM
Robert Wolcott
 
Posts: n/a
Default

I measured the voltage across the bnc connector (disconnected from diode)
again and it was 5.015 volts. The diode was open in both directions with my
diode tester (Fluke 177). What usually causes these to fail?

Thanks,
Bob


"Sam Goldwasser" wrote in message
...
"Robert Wolcott" writes:

I'll give that a try. This diode is part of a relative power meter on my
yag laser. The meter is currently not working and I'm not sure if it is
the
diode or the circuit. The circuit can be seen at:

http://oregonstate.edu/~wolcottr/Yag...0schematic.jpg

Tests I have run include:

Measured the voltage supplied to the diode via BNC connector and it is
5.0
volts


Is the input 5 VDC or 12 VDC? 5 VDC wouldn't peg a 1 mAFS meter since
there is a 10K current limiting resistor.

placed a 1k resistor across the BNC connector and the power meter was
pegged.


Sounds consistent with 12 VDC input and the circuit working properly.

Hooked up the photodiode to the circuit and shined a 5mw diode laser into
it
and there was no reading (direct illumination).


Do the tests above but sounds like it's bad.

Does this sound about right?


Yep. You can also test the photodiode on the diode check range of your
DMM. It should test like a silicon diode. I bet it tests open both ways.

--- sam | Sci.Electronics.Repair FAQ Mirror:
http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ:
http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites:
http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the
excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above
is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.



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Old January 4th 05, 11:48 PM
Sam Goldwasser
 
Posts: n/a
Default

"Robert Wolcott" writes:

I measured the voltage across the bnc connector (disconnected from diode)
again and it was 5.015 volts. The diode was open in both directions with my
diode tester (Fluke 177). What usually causes these to fail?


They can just fail on their own. In that circuit, current is safely
limited by the 10K resistor. Not much other than excessive current
or excessive reverse voltage could damage a low speed photodiode.

Just install any cheap photodiode with a large enough active area and
see if it works. A $2 one from Digikey would likely work just fine.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.

Thanks,
Bob


"Sam Goldwasser" wrote in message
...
"Robert Wolcott" writes:

I'll give that a try. This diode is part of a relative power meter on my
yag laser. The meter is currently not working and I'm not sure if it is
the
diode or the circuit. The circuit can be seen at:

http://oregonstate.edu/~wolcottr/Yag...0schematic.jpg

Tests I have run include:

Measured the voltage supplied to the diode via BNC connector and it is
5.0
volts


Is the input 5 VDC or 12 VDC? 5 VDC wouldn't peg a 1 mAFS meter since
there is a 10K current limiting resistor.

placed a 1k resistor across the BNC connector and the power meter was
pegged.


Sounds consistent with 12 VDC input and the circuit working properly.

Hooked up the photodiode to the circuit and shined a 5mw diode laser into
it
and there was no reading (direct illumination).


Do the tests above but sounds like it's bad.

Does this sound about right?


Yep. You can also test the photodiode on the diode check range of your
DMM. It should test like a silicon diode. I bet it tests open both ways.

  #8   Report Post  
Old January 5th 05, 07:10 PM
Bradley1234
 
Posts: n/a
Default


"klasspappa[remove]" wrote in message
...
A diod is a diod, not a resistor.
See it as a current source, and put it into a opamp to form a current to
voltage converter...


A diode is a variable resistor.

the circuit reacts around the depletion region to increase or decrease it.
When the p type and n type silicon meet, the charges mix to form a neutral
region which is resistive. if the applied electricity is on one side it
makes that neutral region expand out, if its the other way the neutral
region is compressed

But silicon has unique properties where it can convert energy from light or
heat into current. In the photodiode's case if I recall, it can use light
or heat to control that neutral region


  #9   Report Post  
Old January 5th 05, 07:43 PM
Sam Goldwasser
 
Posts: n/a
Default

"Bradley1234" writes:

"klasspappa[remove]" wrote in message
...
A diod is a diod, not a resistor.
See it as a current source, and put it into a opamp to form a current to
voltage converter...


A diode is a variable resistor.

the circuit reacts around the depletion region to increase or decrease it.
When the p type and n type silicon meet, the charges mix to form a neutral
region which is resistive. if the applied electricity is on one side it
makes that neutral region expand out, if its the other way the neutral
region is compressed


Not really.

--- sam | Sci.Electronics.Repair FAQ Mirror: http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ: http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites: http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.
  #10   Report Post  
Old January 5th 05, 08:05 PM
Bradley1234
 
Posts: n/a
Default


"Sam Goldwasser" wrote in message
...
"Bradley1234" writes:

"klasspappa[remove]" wrote in message
...
A diod is a diod, not a resistor.
See it as a current source, and put it into a opamp to form a current

to
voltage converter...


A diode is a variable resistor.

the circuit reacts around the depletion region to increase or decrease

it.
When the p type and n type silicon meet, the charges mix to form a

neutral
region which is resistive. if the applied electricity is on one side it
makes that neutral region expand out, if its the other way the neutral
region is compressed


Not really.


Then please to explain me how silicon diodes work? All this time I thought
it was the depletion region but its something else?

If my simplified explanation of the solid state physics involved in PN
junctions is incorrect Im grateful to learn where Im wrong.



--- sam | Sci.Electronics.Repair FAQ Mirror:

http://repairfaq.ece.drexel.edu/
Repair | Main Table of Contents: http://repairfaq.ece.drexel.edu/REPAIR/
+Lasers | Sam's Laser FAQ:

http://repairfaq.ece.drexel.edu/sam/lasersam.htm
| Mirror Sites:

http://repairfaq.ece.drexel.edu/REPAIR/F_mirror.html

Note: These links are hopefully temporary until we can sort out the

excessive
traffic on Repairfaq.org.

Important: Anything sent to the email address in the message header above

is
ignored unless my full name is included in the subject line. Or, you can
contact me via the Feedback Form in the FAQs.





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