Electronic Load Project - TLV171 & IRFP250 with KiCad Files

[t1d]

SDS00008.png shows a periodic signal based on a PWM nearby - maybe a switching powersupply nearby which let me assume that this is not a real signal.

Maybe you could send pictures how you measured. I assume that you didn`t measure with the spring at the probe. Instead you measured with the long GND-Clip, which resumes in a lot of hf-pickup, specialy at low voltages. Search net for "how to probe low voltage signals".

btw: would be nice if you could switch off the unused channels.

And please set the active channel to one of the horizontal gridlines so that it is easier to calculate the DC-part of the signal. Best would be that you don`t move vertikal if possible, just change Volts/div or time/div so that it is easier to compare different screenshots.

Mk, yes, I had used the probe ground wire. The probe pin was on the input of R9 and the ground was made to the Meter Input "GND"/0 (which is common to the "GND"/0 plane.
- I still do not have a camera.
- Unused channels are turned off.
- Active channel moved to grid line.

All of the three following screenshots (9, 12 &13) were taken with the x10 probe ground spring on the GND of C1 and the probe pin spanned to the input of R9 with a modified header pin. The header pin was secured to the probe pin with it socket head clip and a bit of Blue Tack. Contact was maintained with hand pressure, only. This arrangement was fiddley, to say the least, and had me in a sweat…

The Stop Function was utilized. The Run Function shows much more noise, of course.

I have learned that the cursor information block, for my make/model scope cannot be moved. I darkened its background, to help legibility.

I will retest the wall wart, under a load, as Kleinstein suggests. Hopefully, tonight, if I can catch my breath. To do so, I need suggestions for a proper breadboard arrangement, please. The wall wart is 12vac/2a. I have a 10 Ohm – 5 Watt – 5% power resistor… And lots of common resistor and pot values. Bridge rectification, too...

Thanks, again.

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x10 probe at 0.0a

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x10 probe @ 0.5a

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x10 probe @ 2.325a

[Kleinstein]

For testing the 12 V source, the 10 Ohms resistor would get some 15 W. So this could only work for short time load. It could still be used for a short time (several seconds) and this enough to get a reading from the scope.

Alternative some 100 Ohms cold also be used for loading.

[t1d]

More Testing, per Kleinstein's request.
x10/Spring
Wall Wart. Off test rig. On breadboard. 20 Ohms of resistance (2 x 10 Ohm), in series. Measured from input of Resistor #1 across to output of Resistor #2.

Note the large PP voltage swing of 34v. (60Hz mains hum?) I checked my probe and it is still on x10. Is this amplitude even possible, with a 12vac Wall Wart? If I tested it correctly, that must be an issue; correct? I am tired, now, but I will put a multimeter on it, asap.

[t1d]

More Testing.
x10/Spring
DUT/SMPS = Professional 12vdc/55a Battery Charger. Off test rig. On breadboard. 20 Ohms of resistance (2 x 10 Ohm), in series. Measured from input of Resistor #1 across to output of Resistor #2.
Note: The charger has extremely long supply lines... 16 feet, is my guess. Coiled.

3.1MHz. 2.04v PP amplitude.

[t1d]

I have a Brymen BM869s DMM. I used it to check the Wall Wart supply, regarding the 34.6vac PP voltage swing. I used the Max/Min feature. The max only read 11.75vac. It also has a "Crest" feature, but that only works with dc. So, what do you think is going on, with the 34.6vac PP swing, and what do you suggest for the next step?

[mk_]

More Testing.
x10/Spring
DUT/SMPS = Professional 12vdc/55a Battery Charger. Off test rig. On breadboard. 20 Ohms of resistance (2 x 10 Ohm), in series. Measured from input of Resistor #1 across to output of Resistor #2.
Note: The charger has extremely long supply lines... 16 feet, is my guess. Coiled.

3.1MHz. 2.04v PP amplitude.

Your focus sits onto an irrelevant signal. Thats noise frome somewere else, not from your pcb.

 Set the timebase to 5ms/div, aactivate the 20MHz filter in channel 1 and show some more pictures with 0, 0,5, 1, 2A loadcurrent.

[Kleinstein]

The supplies both look high ripple. So one has to expect some of the ripple to be visible. So much of the visible signal is just from the supplies.

For the wall wart, there might be a contact problem with the ground wire - the AC voltage does not make that much sense. So it could be common mode background with the scope ground not having contact With just a rectifier the ripple should be 120 Hz.

What type of wall wart is this:  heavy with classical transformer or SMPS type.

[t1d]

Set the timebase to 5ms/div, aactivate the 20MHz filter in channel 1 and show some more pictures with 0, 0,5, 1, 2A loadcurrent.

Thank you; I will do as you instruct.

[t1d]

What type of wall wart is this:  heavy with classical transformer or SMPS type.

It is the heavy type classical transformer. It does not have an Earth GND connection; it is floating, with respect to Earth. The oscilloscope has a proper ground to Earth.

For the wall wart, there might be a contact problem with the ground wire - the AC voltage does not make that much sense. So it could be common mode background with the scope ground not having contact With just a rectifier the ripple should be 120 Hz.

- The E-Load circuit supply is branched off of only one leg of the AC supply; AC1.
- The supply is (only) half rectified.
- What is referred to as GND, on the schematic, is actually 0/Virtual GND.
- This virtual ground is tied/returns to AC2.
There was much discussion in developing the supply in this manner. Just as a reminder, here is the drawing, of that portion of the circuit.

[t1d]

As requested by mk, tests were performed at 0.00a, 0.50a, 1.00a, 1.50a, 2.00a and 2.32a loads with the 20Mhz filter.

X10/Spring/20MHz filter applied

All of the following screenshots were taken with the x10 probe ground spring connected to GND of C1 and the probe pin spanned to the input of R9. A header pin was soldered to GND of C1, for convenience of connecting the probe spring.

Contact was maintained with hand pressure, only. The hand pressure could/was manipulated to obtain two types of results.
A) While the scope was in the Run Mode, hand pressure was manipulated, until the wave naturally settled into a recognizable form. It was then captured with the Stop Function. This connection resulted in a greater amplitude of the wave form than B, following. See TL and TS pngs.
B) The pin was connected without manipulation (just naturally placing the probe pin on the input of R9). The wave form was not recognizable, until captured with the Stop Function. This resulted in a lower amplitude of the wave form. See NTL and NTS pngs.
(Which is the proper means of testing?)

File Coding
x_xx = Amperage being sunk
TL = Hand manipulation A, above. Zoomed in.
TS = Hand manipulation A, above. Zoomed out.
NTL = No hand manipulation B, above. Zoomed in.
NTS = No hand manipulation B, above. Zoomed out.
SDS00021-24 = 2.00a and 2.32a loads, but they got out of order; order unknown.

The Stop Function was utilized. The Run Function shows much more noise, of course.

Conclusion: A 50KHz recurring ring/oscillation, of varying amplitude, is evident across all load values. What should I try, as a cure?


0.00a Load
No Hand Manipulation
Zoomed in.
Zoomed out.

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0.00a Load
Hand Manipulation
Zoomed in.
Zoomed out.

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0.50a Load
No Hand Manipulation
Zoomed in.
Zoomed out.

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0.50a Load
Hand Manipulation
Zoomed in.
Zoomed out.

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1.00a Load
No Hand Manipulation
Zoomed in.
Zoomed out.

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1.00a Load
Hand Manipulation
Zoomed in.
Zoomed out.

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1.50a Load
No Hand Manipulation
Zoomed in.
Zoomed out.

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1.50a Load
Hand Manipulation
Zoomed in.
Zoomed out.

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2.00a Load
Hand Manipulation
Zoomed in.
Zoomed out.

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2.32a Load
Hand Manipulation
Zoomed in.
Zoomed out.

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2.00a and 2.32a Loads
No Hand Manipulation
Zoomed in.
Zoomed out.
Order unknown.

Thank you for your continued patience and help!

[Kleinstein]

The signals all look like ringing as a consequence of the voltage source with a lot of ripple / spikes. So the first point would be to get a reasonable clean voltage source to test the circuit.  With a high ripple voltage source there will be some response to it, especially if still to a low speed.

It would also help to use more than just 1 channel, e.g. having one for the signal of interest (e.g. voltage across R9) and the other to something like the voltage of the source.
For the beginning just 1 or 2 pictures at a time should be enough - otherwise the thread only gets hard to read.

[t1d]

Firstly, Kleinstein, thank you for all you do to help me. You are most patient and dependable...

The signals all look like ringing as a consequence of the voltage source with a lot of ripple / spikes. So the first point would be to get a reasonable clean voltage source to test the circuit.  With a high ripple voltage source there will be some response to it, especially if still to a low speed.

I think I need clarification, here... When you say "voltage source," do you mean the SMPS Battery charger (the Device Under Test,) or do you mean the Wall Wart (Circuit) Power Supply?

- If the DUT Battery Charger, I could swap it out for a transformer having a full bridge rectifier and voltage regulator... That's about as clean as it is going to get...
- If the Wall Wart, I can try a different transformer...
Instructions?

It would also help to use more than just 1 channel, e.g. having one for the signal of interest (e.g. voltage across R9) and the other to something like the voltage of the source.

I think I can manage that, on the next test...

For the beginning just 1 or 2 pictures at a time should be enough - otherwise the thread only gets hard to read.

Well, I was trying to supply exactly what mk had asked for... Yes, it does get to be a bit much...

Which was the proper waveform type to capture, the hand-manipulated, settled waveform, or the just-touch-the-resistor-pin waveform?