Hi,

I'm mystified as to a confusing problem concerning a dual diode package and the way it works. Having connected one diode of the package to a simple circuit ie 9v battery and 10K resistor, I find that the voltage on the cathode which is 9v also appears on the anode of the diode which is not connected.


Can anyone explain why this is?

Thanks for any help.

 

Hi Baldrick.
Welcome to AAC.
Do you have a diode model type code you could post.?

E

 

Reverse biased diodes are not perfect insulators, so a small amount of current can leak “backwards”. Considering that a typical digital voltmeter has an input resistance of 10 Megohms, it does not take much (leakage) current at all to develope considerable voltage.

 

Hi,

I'm mystified as to a confusing problem concerning a dual diode package and the way it works. Having connected one diode of the package to a simple circuit ie 9v battery and 10K resistor, I find that the voltage on the cathode which is 9v also appears on the anode of the diode which is not connected.


Can anyone explain why this is?

Thanks for any help.

The package is MBR6045WT, I've had this problem on other packages as well.

 

Hi B,
As my colleague points out leakage, especially on Schottky diodes and a high resistance DVM will show the voltage you see.
E

 

Hi,
we need more detailed description of your test. Where the battery plus was connected to? Where the voltmeter probes were connected?

 

Hi B,
As my colleague points out leakage, especially on Schottky diodes and a high resistance DVM will show the voltage you see.
E
View attachment 299050

Thanks E for replying to my question and taking time to draw the circuit, much appreciated! The term leakage is that the flow of forward electrons across the diode junction? The DVM being about 10M will really cause the voltage to appear near the 9v supply voltage? So when Diode 1 has a voltage source applied the leakage disappears, is that how it works?
Thanks.

 

Hi,

I'm mystified as to a confusing problem concerning a dual diode package and the way it works. Having connected one diode of the package to a simple circuit ie 9v battery and 10K resistor, I find that the voltage on the cathode which is 9v also appears on the anode of the diode which is not connected.


Can anyone explain why this is?

Thanks for any help.

Could you please provide a sketch of exactly how you have your battery, resistor, and diode package connected?

When you say that the voltage on the cathode is 9 V, what is that relative to? Where are you putting the other probes of your meter?

 

"The same voltage appears" makes me ask "how do you know that???" In many instances the results are dependent on what is used to measure, and in basic electricity that is especially true. We learn that early in engineering classes.
Voltage drop is dependent on current flow, and so if there is no current flow there is no voltage drop. So now it is fair to ask what was used to measure the voltage, and how much current flowed to provide that measured voltage. The answers to those questions will provide the explanation being sought.