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Just a diode

J

Jiks

Jan 1, 1970
0
What will you see if u measure a sensitive Voltmeter to the end leads
of a Diode ?
 
J

John Popelish

Jan 1, 1970
0
Jiks said:
What will you see if u measure a sensitive Voltmeter to the end leads
of a Diode ?

If it is in the dark, zero.
 
S

Steven Swift

Jan 1, 1970
0
If it is in the dark, zero.

True if a perfect voltmeter, but most likely you'll see a little leakage
current and hence a small voltage.
 
J

John Popelish

Jan 1, 1970
0
Steven said:
True if a perfect voltmeter, but most likely you'll see a little leakage
current and hence a small voltage.

Are you claiming that a diode produces power (pushes current with a
self generated potential drop)?
 
M

Michael A. Terrell

Jan 1, 1970
0
Steven said:
True if a perfect voltmeter, but most likely you'll see a little leakage
current and hence a small voltage.


Small signal diodes can rectify stray RF and AC fields that are
picked up on the test leads.


--
Service to my country? Been there, Done that, and I've got my DD214 to
prove it.
Member of DAV #85.

Michael A. Terrell
Central Florida
 
J

Jiks

Jan 1, 1970
0
But to rectify the effect..... dont the stray Rf signals be greater
than .6 V [ for Si ] ???
 
R

redbelly

Jan 1, 1970
0
Jiks said:
But to rectify the effect..... dont the stray Rf signals be greater
than .6 V [ for Si ] ???

Nope. The nonlinearity of the i-v curve creates a partially rectified
(and therefore non-zero) dc signal. Try it yourself. (Use individual
leads, not coax.)

Mark
 
K

kell

Jan 1, 1970
0
Jiks said:
What will you see if u measure a sensitive Voltmeter to the end leads
of a Diode ?
If you have the meter set to measure volts, zero.
If you have the meter set to measure current, zero.
If you have the meter set to diode test, you'll see the forward voltage
drop across the diode for whatever current the meter puts out at diode
test, usually something on the order of a milliamp. Assuming you have
the leads' polarity correct. Something around six tenths of a volt
give or take a tenth, but of course it depends on the particular diode
and the current the meter delivers through it.
 
J

jasen

Jan 1, 1970
0
What will you see if u measure a sensitive Voltmeter to the end leads
of a Diode ?

most of the time nothing at all, but if you can shine some (considerable
amount of) light on the junction you'll see the photovoltaic effect in action.

Try a glass-encapsulated diode (1n914, 1n4148) and use a magnifying glass
to focus sunlight. it shoulde register on any halfway decent milivoltmeter.

it works with LEDs too.

Bye.
Jasen
 
P

Peter M. Groen

Jan 1, 1970
0
John said:
Are you claiming that a diode produces power (pushes current with a
self generated potential drop)?

No. He's claiming a voltage picked up by the test-leads (Hence the
word "Sensitive Voltmeter") due to RF and AC signals in the air.

Peter
 
P

Peter M. Groen

Jan 1, 1970
0
John said:
But then, it is not in the "dark". ;-)

And how is light of influence to RF/AC signals when not put into the context
of Quantum Physics? ;)

Peter.
 
J

John Popelish

Jan 1, 1970
0
Peter said:
John Popelish wrote:




No. He's claiming a voltage picked up by the test-leads (Hence the
word "Sensitive Voltmeter") due to RF and AC signals in the air.

But then, it is not in the "dark". ;-)
 
J

John Larkin

Jan 1, 1970
0
Small signal diodes can rectify stray RF and AC fields that are
picked up on the test leads.

Johnson noise, too.

John
 
S

Steven Swift

Jan 1, 1970
0
Are you claiming that a diode produces power (pushes current with a
self generated potential drop)?

No, of course not. But the best voltmeters made still have picoamps of leakage
and this will generate a voltage. Also thermal mismatches will generate
enough current to show a voltage across the diode. If sensitive is defined
to be ZERO input current and isothermal leads, then the diode will read
zero in the dark.
 
J

John Popelish

Jan 1, 1970
0
Steven said:
No, of course not. But the best voltmeters made still have picoamps of leakage
and this will generate a voltage. Also thermal mismatches will generate
enough current to show a voltage across the diode. If sensitive is defined
to be ZERO input current and isothermal leads, then the diode will read
zero in the dark.

What is the answer if you are trying to not confuse a beginner?
 
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