half-wave rectified filtered circuit/oscilloscope measurement

[Henry9316]

Hello everyone, I hope I can get some help on this basic issue I am having. The online University I am with will not assist me, so hopefully I can quickly get some help here.

I have the NI myDAQ, I need to construct Half-Wave rectified Filtered circuit with a 2.2kOhm resistor, I also use multi-sim to confirm waveform measurements. Everything is fine on Labview when compared with multisims Tektronix Oscilloscope before I connect a 100uF capacitor heres my comparison:

The breadboard is just the Diode in with a 2.2kOhm resistor in series, I am not sure if the Analog inputs for the LabView Oscilloscope are setup correctly this is the waveforms I get:

This satifies my simple comparison to the Multisim circuit, since I have been here for a few hours playing with the Analog Input probes I know something is not right from the measurements I get.

With a 100uF capacitor in parallel:

I think the issue is how I have the Analog inputs and AGND wired, I am not sure this is where I would really like some assistance or any kind of help. Once I get this set up right I will be able to take measurements for the Ripple Frequency, DC Load Voltage, P-P Ripple and then Move on to a Full-Wave rectified circuit. I just started a course and recieved the myDAQ.

[Henry9316]

Still here, trying to get the perfect waveform, here is what I Have after cleaning up the breadboard and tightening up the myDAQ screws and terminal:

[Henrik_Volkers]

In your simulation, have a look at the current out of your signal generator.

Compare it with the output current specification of your myDAQ 😉

[crossrulz · Accepted solution]

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@Henrik_Volkers wrote:

Compare it with the output current specification of your myDAQ 😉

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Here is a link to the specification: http://www.ni.com/pdf/manuals/373061f.pdf

Henrik hit it on the head.  The myDAQ can, at most, output 2mA with the Analog Output.  So with a 2.2kOhm load, that puts you at 4.4V without the diode.  The diode will also require some amount of current.  By my estimates, about 1mA (your peak is ~2.5V, divide by the 2.2kOhm to get ~1mA).  You only see this on the positive side of the sine wave since the diode is blocking all current on the negative side.

So the lesson here is to make sure your outputs have enough power to do what you want.  You can go get a simple op-amp from digikey and use a Voltage Follower setup to get the current up.  You will likely need another power supply or two (+12V and -12V) to power the op-amp.

[Henry9316]

Well my assignment for this lab was to use Multisims center tapped rated transformer, step it down with a 30:3 winding and use that secodary voltage for the physical part for the myDAQ. This just really complicated things and I ended up using a "regular" transformer , here is the full snippet:

Also right now, since I am still trying to complete this basic assignment, so that I move on(I am a bit behind), I was noticing how the myDAQ oscilloscope's measurement of the Vp-p was dropping with the capacitor, I got a measurement of the voltage drop across the resistor with my DMM. I will have a look at the Specs, i did not think that this would go over the myDAQs limits....

Thank you for the consideration, I did not calculate the current draw for the load. I have been up all night watching videos and reading my textbook, "Malvino" along with Kleitz's book for digital electronics.

[Henry9316]

How does the wiring looking for the myDAQ? 

Am I in the right ball park? I haven't connected the 2nd 1N4001 for the Fullwave.... At least I am getting better at snipping desktop images.......

[Henry9316]

Sorry for grinding the dead horse some more. But I think I will just lower the function generator voltage to around 1Vp-p.  The assignment I am working on did not specifiy any voltage. I was told was use multisim with a center tapped transformer to get the secondary voltage for the myDAQ implentation. So I think the point to take away was the calculations, plus the work with the Diodes..... You know what really threw me off was the fact that the "Rated center Tapped transformer, located in the Basic Rated virtual components in multisim won't work. I was even trying examples right out the book and still got nothing, I know I must be missing something in my brain that is not clicking.... The university expects way to much from the suckers that pay into thier style of teaching...

[Henry9316]

I dont know what has happened over the last 12 hours, I am not even sure If my sense of reality is still there, but I managed to get this:

[Henrik_Volkers]

Sorry to say that....

BUT What have you learned?

In my first post I asked you to look at the generator output currrent in your simulation.

OK, crossrulz direktly pointed you to the output limit of the AO ... HOWEVER  ..

/TeacherModusON

Have you looked at the output current of your simulation (with and without 100µF), can you! explain! the current traces??

Nice if simulation and measuremt matches... somehow....    BUT it's all for naugth IF.YOU.CAN'T.EXPLAIN.IT!!

/TeacherModusOFF