Hacking A Dynamic Electronic Load Circuit To Use Function Generator? Solved

[JS]

The diode in your drawing seems fine but should be in parallel with the resistor, not in series.

Then, all the opamps driving gates same thing but the diode in the other direction. This will hold all the opamps to getting saturated while the load is off (negative input) and recover much faster and with smaller wind up than if the diodes weren't there.

The pot can be the attenuator. 100k summing resistor, 10k pot, 50Ω input, nothing needs to change there.

JS

[t1d]

Hi, JS, Thanks, for your fast reply... Here is how I envision your instructions...

I just want to double check... All the diodes are 2.5v zeners, even though the reference voltage is 2.5v. Correct?

There is not a resistor, in the MOSFET driver op amp circuits... It is a capacitor... I put the zener in parallel, to the cap. Correct?

I think we are almost there! Thank you, so much!

You can't sleep, either, eh?

[JS]

Signal diodes, not zeners, all the rest seems correct

JS

[blackdog]

Hi,

Maybe is it is inspiring to look at this design, fast dummy load with a almost perfect puls response.
A lot of importend info is already placed in the pictures.

The main part.



Power supply, van controler and simple puls generator.



This is the link of my topic on the Dutch electronics website (use google translate )
https://www.circuitsonline.net/forum/view/121338/1#highlight=load+dummy

Kind regards,
Bram

[t1d]

Signal diodes, not zeners, all the rest seems correct
JS

Great JS! I am truly excited; thank you so much.

Is a 1n4148 appropriate? Or, do you suggest something else?

I will finish up the schematic and post a final edition.

I would not have made it, without you. I appreciate you.

[t1d]

Good information, Bram. Thank you, for participating.

Is there an English translation button?

And, please provide the two schematics in a downloadable file format, like pdf, or jpeg.

[JS]

Signal diodes, not zeners, all the rest seems correct
JS

Great JS! I am truly excited; thank you so much.

Is a 1n4148 appropriate? Or, do you suggest something else?

I will finish up the schematic and post a final edition.

I would not have made it, without you. I appreciate you.

Yes, 1N4148 are fine.

JS

[t1d]

Thank you, JS, and all others, for your help, in creating the auxiliary input, for the Function Generator. Here is the completed schematic...

[t1d]

JS,
It has occurred to me that, as an auxiliary FG input is now available, there may not be need, for the on-board 330MHz FG. So, I relocated the aux input, to the controlling op amp input, via a break-before-make switch, and deleted the on-board FG circuitry. Would this work?
Thanks.

[JS]

It will work, but it might still be useful for some quick check, if the opamp is integrated in the IC already... Also, if removing the oscilator, the 33k resistor should be changed to closer to 50k... 51k or 47k will do fine.  (The obe to the non inverting input from the remaining opamp in the picture)

JS

[t1d]

Terrific, JS! I think we can mark the post as "solved," now...

Thank you, so much, for all your wonderful help. You have shared your time, effort and expertise so graciously. I appreciate you!

[JS]

Seems fine for me, did you placed the diodes in every other opamp? Otherwise they will still be in saturation and will take a while to recover after the input goes below zero.

JS

[t1d]

Hi, JS,

Yes, Sir, for each one, as you had instructed. See the pfd, at post #32.

Thank you.

[JS]

Well, I wait for the full docs then, or a PCB if you end with an spare one or two... I'd be willing to help with the span of it as well, I made a DC load recently but a bit whimpy and lacks the external input or the dynamic capability FWIW. It does work in CV though, which is nice for testing CC supplies, or current limits.

JS

JS

[t1d]

Sure, JS, I would be glad to share any and all.

I posted the completed KiCad files, for the original three versions, of Jay's design, which include his oscillator, on his thread. https://www.eevblog.com/forum/projects/dynamic-electronic-load-project/

I will post the KiCad files, for our two hacks which inject a function generator signal... one with Jay's original oscillator in place... and the other being my preference of the circuit without the original oscillator. But, I am too tired to do that tonight... I will have to round up the custom libraries, and such, and zip it up. Tomorrow, I imagine...

I am sorry, but I do not know what you intend, by "I'd be willing to help with the span of it as well..."

I am sending you a pm, to discuss the PCBs...

[t1d]

I bread-boarded the control circuit, earlier in the evening. I could not sleep, so I did a power-on test. Using a LM741 op amp, from the op amps that I have on hand, I was able to maintain a very acceptable square wave, to 5000KHz.

I don't know the correct term, but there was "echoing." However, the shape was not greatly deformed.

Interestingly, at lower frequencies, there was a prominent spike, at the top of the rising edge. It disappeared, the faster I tuned it. I would have thought that it would have appeared, at faster speeds, not slower.

[JS]

I could help drawing the pcbs, that's what I meant.

The spikes appear in fast edges, as you come closer to the freq limit the spikes are seen from closer and it can look as the echoing you mention (reflections?) which would need to be traced out but improper termination of wires is usually the peoblem, hence the suggestion for the 50Ω termination at the input. Something similar should be done at the resistor output but pretty hard to manage for the actual load connections, but anything there will be seen by the source, the load and the used meter so that's not as bad. Slowing down the design makes it less overshooty...

JS

[t1d]

Here are the KiCad files, for the Function Generator Injector versions of Jay_Diddy_B’s ingenious Dynamic Electronic Load design. Find Jay’s Thread, here https://www.eevblog.com/forum/projects/dynamic-electronic-load-project/

KiCad is a powerful, FREE program, to make schematics and board designs. Find it here: http://kicad-pcb.org/. It will be very easy, to create PCB boards, with the files.

What Is included
Circuit development branched into two divisions; Jay’s original LT1013 Dual (Power) Supply model, which includes his oscillator section, and my model of the LT1013 Dual (Power) Supply, having Jay’s oscillator section removed.

The schematics are ready for you to use, as is. You will only need to:
- select your choice of model,
- verify your choice of op amps and MOSFETs, (See following!)
- select your components and
- create your own PCB board design.

Feel free to customize. Use components that you like, or have in stock. The selection of the component types, for the board, is done, with the CvPCB function, found on the schematic page. Whatever you plan to do, you will be miles ahead, using these files.

A note on customization… Changes in components will effect performance; you need to know what you are doing, or get help. If you change the number of MOSFET nodes, you will need to calculate the new value, for their meter output resistors. If you want to use a different op amp, you will have to change the connections, to the new op amp’s pinout, as the LT1013 does not have a common pinout. To change to a quad op amp having a common pinout, it might be easiest to go to Jay’s thread, download the LT1014 project files (Post #144) and add to it your choice of Function Generator Injector method. You will find other circuit variations there, too.

The wattage, seen by the shunt resistors, can be spread over parallel resistors, but it does limit the accuracy. For accurate current shunts, one has to operate them at well below nominal power; at nominal power the self heating is usually too high and causes excessive change in the resistor value. The 0.1 Ohms shunts should operate at something like up to 1 A and thus 100 mW. Still it would make sense to choose resistors that are good for a 0.5 or 1 W power rating. 250 mW types are too small – even with just 100 mW used. So, the value of parallel shunt resistors equals 0.1 x number of parallel shunt resistor used.

The value of the meter output resistor should be 50 ohms x number of output stages. For example, with four output stages use 200 ohm resistors.

A Note To SMD Users
All the resistors can be 1%. The cost of 1% versus 5% is minimal. Most parts can be 0603, 0805 or 1206 whatever you are comfortable working with. You need 2512 resistors for the shunts. The 2.2uF/100V should be 100V 1210 size.
A Note To Non-KiCad Users
KiCad allows the selection of component footprints, regardless of their schematic symbol. 01x03 connectors, labeled as "Wire Pads," are used here, to represent the selection of Wire Pads, on the PCB board. This method enables the use of separate Control and MOSFET PCB boards. However, these connections should be hard wired. Because of high power draws, connectors should not be used, to connect boards, to MOSFETs. If a single, Control-MOSFET board is used, remove these pads, from the circuit.

Use At Your Own Risk
You are free to make any and all use, of the files. However, in doing so, you release all contributors and me from absolutely all liability. I am not an electrical engineer. I do not guarantee that there are no mistakes. You must verify absolutely everything, for yourself. I did not design the operational circuit.

[t1d]

I would appreciate it, if someone would download the KiCad files, verify that they operate properly and post back, here, to let me know. Thank you, for this help.

[t1d]

The complete project release can be found here:
https://www.eevblog.com/forum/projects/electronic-load-project-ltv171-irfp250-with-kicad-files/msg1840739/#msg1840739