1N4001 Diode Question --- Building a Test Load

[Kaokin]

So i went to radio shack today to purcahse all the components needed in order to construct the test load that is seen on this webpage:

It can be done - Laser driver

I found all the components easily but when i got home to build the test load and read the page again, i encountered a question in the math for this test load! The site says that each 1N4001 diode is supposed to equal a voltage drop of .7 Volts, but upon reading the back of the diode package it states that the "Foward Voltage Drop (VF) at (lf) = 1.6V"

Am i reading this incorrectly and missing something or is this correct and i need to rework the calcualtion for the test load?


I also couldnt find a 1 ohm 1 watt resistor so i bought a 1 ohm 10 watt resistor; this doesnt make a difference right???

 

[Flaminpyro]

The resitor is fine it's better than fine, the diodes are a different story you must have gotten some special diode like a shottkey or something, are they 1n4001 type's. in order for the ckt you have to work it requires diodes with a forward voltage drop of 0.7 volts.

 

[Kaokin]

thanks pyro, i was afraid you were going to say that What if i were to use them any way and just use fewer?? for example; the ckt recommends 6 x 0.7v diodes for a total of 4.2v of resistance. If i were to use 3 1.6v diodes in series that would give me 4.8v resistance which should be fine for a blu ray diode correct??

 

[Hemlock_Mike]

That forward drop can be misleading. It depends on the current applied. not always linear.
Test them for voltage drop at ~ 350 mA. a 1N400x diode is usually predictable.

HMike

 

[Meatball]

I was running through a huge pile of diodes tonight, just sorting them out. All of my 1N4001s seems to have a .9 volt drop across them. They are usually fine for me. I wonder what is so different about your diodes then...

 

[Kaokin]

Yah im not sure.... I just went to radio shack and found the only one that matched the diy description and thats what i purchased... here is a link to the actual product:

1N4001 Micro 1A Diodes - RadioShack.com

So to test the diode for Vf drop do i just set my DMM to DC Volts and measure across the diode or do i set it to Ohms or ? Sorry for the noob question, I dont know much about electronics

 

[HIMNL9]

I just have a doubt, at this point ..... is your DMM working good ? ..... put it on diode position and close the leads, if you read zero, or a little (very few) mV, it's ok, if you read, like, more than 004 or 005 mV with the leads in short circuit, then is the DMM the problem.

Also, some cheap units, if have half-charged batteries, instead stop to work, just false all the measures, so check also the DMM battery.

 

[Meatball]

You could also connect the diode to a 3V battery, along with 3, 10 ohm resistors or so, and then just read the voltage across the diode...

 

[Kaokin]

The DMM doesnt seem to be the problem, its a digital autoranging DMM from sears, bought it a few years ago and it really hasnt seen much use, i paid like 50 bucks for it. I set it to the ohm setting and crossed the contact leads and got a measurement of 000.0. I Then set it to the diode setting, and tested across the diode both ways. One way read OL and the other way read 0.508v. So does this indicate a .508v Vf drop?? I just want to make sure i am using my DMM and reading this correctly. Thanks for all the help!!

 

[dirtbiketrailsrider]

thanks pyro, i was afraid you were going to say that What if i were to use them any way and just use fewer?? for example; the ckt recommends 6 x 0.7v diodes for a total of 4.2v of resistance. If i were to use 3 1.6v diodes in series that would give me 4.8v resistance which should be fine for a blu ray diode correct??

Go down to the test load description
It can be done - Laser driver

 

[ElektroFreak]

If they're 1N4001 diodes, then they will provide a .7V drop. It's that simple. There is no need to measure them or anything like that. As long as they are 1N4001 diodes, they will work. I would be surprised if RS put the wrong diodes in the package, so therefore as long as the package says they are 1N4001 diodes and the diodes themselves say 1N4001, they will work.

 

[Kaokin]

ok thanks, Ill try making the test load and hope it works!! :::Crosses Fingers:::

 

[lasersbee]

And if you need 1 Ohm Test Load resistors look here....

http://laserpointerforums.com/f64/free-1-ohm-test-load-resistors-42409.html

Jerry

 

[aXit]

If they're 1N4001 diodes, then they will provide a .7V drop. It's that simple. There is no need to measure them or anything like that.

Not entirely true... Vf depends on current.

Link:1N400x Diode Family Forward Voltage

 

[HIMNL9]

^ True ..... and it's easy to see it, if you want to check what is in your test load ..... just connect it to a power supply that can change the current, and directly measure it on one of the diodes with different currents through the load.

Anyway, for the use that we do, the fact that it's 0.75 at low current and 0.9 at high current is not so important

 

[aXit]

It was more to explain the .508V result that kaokin got.