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1N4007 diode.

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RhapsodyOfFire

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Hello to all!
I have a 1N4007 diode which I measure has 5.2 megaohms resistance positive to negative. The opposite resistance is so high I cannot measure it.
But in one article here https://www.ehow.com/how_7556262_test-1n4007-diode.html it says there must be short between anode and cathode from + to - and big resistance - to +.
Only the second part of this is true. Is the diode damaged? Also is it rectifying DC to aroud 1000 volts and why does it say "Reverse voltage" in this article https://www.futurlec.com/Diodes/1N4007.shtml or is it the voltage the diode can sustain while working in reverse and not allowing it to pass in reverse direction?
This diode is on a scheme for power inverter on an LCD display ;).
Something is causing a short circuit between + and - right after the bridge rectifier but the bridge rectifier is okay testing each of it's four diodes.

While the diode is soldered on the board I measure 159 ohms only and the voltage measuring diodes it 0.074 in both directions. So there must be a parallel resistance near it connected but why when measured as external I get 5.2 mega ohms... I am sure I don't mistaken Mega with milli because it doesn't measure short circuit between positive and negative lead on the diode.
 
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I think your diode is bad.

Current should flow in one direction and not in the other. When current is flowing there will be a 'forward' voltage of about 0.7 volts. When the diode is blocking current the 'reverse' voltage can be up to 1000 volts with out breaking the diode.
 
Is it possible that I measure very high resistance because of the low voltage I use - around 2 volts of the ohm meter. Maybe if I measure with like 10 volts multimeter I would get little resistance? Just a theory :D.
 
My multimerter measures resistance with 200mV which is not enough to make a silicon junction conduct. It uses about 4.5V on "diode test".

A 1N4007 should conduct when its forward voltage is about 0.7V.
 
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So the diode is bad thanks! I measured it with around 2.4 volts forward diode test.
How do you say what is the maximum forward (operating) voltage of a diode? In the characteristics I find only reverse voltage of about 800-1000 volts, but not an usual P-N junction voltage :(.
 
So the diode is bad thanks! I measured it with around 2.4 volts forward diode test.
How do you say what is the maximum forward (operating) voltage of a diode? In the characteristics I find only reverse voltage of about 800-1000 volts, but not an usual P-N junction voltage :(.

hi,
Look at this image for the 1N4xxx series diodes.
 
But this diode was connected in serial right after the bridge rectifier so it should withstand at least 200-300 volts DC but the graph mentions only 1 volt and 20 amperes which is a lot :D. audioguru 20A = 1.0v ;) check the last graph again.
 
you are confusing forward and reverse voltage.

forward voltage is drop when diode is conducting current (forward biased). this is normally in 0.6 - 1V range for rectifiers and 1.6 - 3.5V for LEDs.

reverse voltage is what diode has to withstand when reverse biased (not conducting). this is usually 50 - 1000V for rectifiers and couple of volts for LEDs.

1N400x series diodes are all 1A diodes but with different voltage rating. 1N4007 is rated 1kV so it should have no problem with 300-400V.
current rating is 1A which is what diode can do in continuous operation. the last graph shows current values that greatly exceed the 1A, even reaching 20A.
but look closer and you will see that this is not continuous operation, it is a short pulse. in this case forward voltage drop is about 1.5V. drop is 1V at 2A, not 20A.
 
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