Author Topic: Dynamic Electronic Load Project  (Read 144753 times)

0 Members and 1 Guest are viewing this topic.

Offline Jay_Diddy_BTopic starter

  • Super Contributor
  • ***
  • Posts: 2731
  • Country: ca
Re: Dynamic Electronic Load Project
« Reply #100 on: August 26, 2018, 11:49:55 pm »

Snip ..

Please clarify the suffix, of the values, of these resistors. I could guess, but that is dangerous.  Such as R19 is a 51R resistor…

R1   100
R2   0.1
R20   100
R21   0.1
R23   3300
R4   3300
R5   0.1
R9   2.2


Resistor values given without m (milli), k (kilo) or M (Meg) are in Ohms, no suffix.

Jay_Diddy_B
 

Offline Jay_Diddy_BTopic starter

  • Super Contributor
  • ***
  • Posts: 2731
  • Country: ca
Re: Dynamic Electronic Load Project
« Reply #101 on: August 27, 2018, 12:00:07 am »
I believe that the difference I noted, between Lt1013/14 models was this...
                            LT1013CDR         Other Models
Temp Max                 70*C                    125*C
Temp Min                   0*C                     -55*C
Input V Offset          0.3mV                   0.8mV
Given that either operational temperature range is acceptable, I take it that the lesser 0.3mV input voltage offset, of the LT1013CDR, would be preferable to the typical 0.8mV, of the other models. Correct?

How important would the better input voltage offset advantage be, in a cost/benefit analysis? LT1013CDR/Dual @ $1.91/unit needs more PCB real estate. LT1014/Quad @ $5.02; YMMV by footprint. For me, at 5 MOSFETS, 4 x $1.91 < $2 x 5.02 and real estate doesn't matter, because 100mm x 100mm is a flat price.

There are some industry standard pinouts for dual and quad op-amps.






These pinouts are widely used and there are many parts that will fit a board designed with these pinouts.


The LT1013 uses a non-standard footprint:



This is not really a good choice, because it means you can't try other op-amps.


The LT1014 use a modified footprint:



There are two extra pins, no connect (nc) pins, but this causes the numbering to change. If you use this footprint, the LT1014 can be used and other parts with the standard footprint will also work.

The full scale voltage on the shunt resistor is 250mV so at 10% of full scale, 25mV, a 0.3mV offset is a little over 1% error. This give you an idea of the sensitivity to the offset voltage Vos.

A total supply voltage >24V is required. The GBW should be 1 MHz or greater.


Regards,

Jay_Diddy_B




« Last Edit: August 27, 2018, 12:02:54 am by Jay_Diddy_B »
 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #102 on: August 27, 2018, 01:31:50 am »
There are some industry standard pinouts for dual and quad op-amps.
These pinouts are widely used and there are many parts that will fit a board designed with these pinouts.
The LT1013 uses a non-standard footprint:
This is not really a good choice, because it means you can't try other op-amps.
The LT1014 use a modified footprint:
There are two extra pins, no connect (nc) pins, but this causes the numbering to change. If you use this footprint, the LT1014 can be used and other parts with the standard footprint will also work.
E-x-c-e-l-l-e-n-t (cautionary)information..
The full scale voltage on the shunt resistor is 250mV so at 10% of full scale, 25mV, a 0.3mV offset is a little over 1% error. This give you an idea of the sensitivity to the offset voltage Vos.
For my personal need and purpose... to build a good, daily, bench load... and not to do further experimentation, I think I will go with the LT1013CDR.
 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #103 on: August 27, 2018, 01:34:26 am »
Resistor values given without m (milli), k (kilo) or M (Meg) are in Ohms, no suffix.
I like an "R," but that's just me... So, is it okay to release the KiCad File?
 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #104 on: August 27, 2018, 02:02:37 am »
I know that the shunt resistors need to be 1%, IIRC. Are there any other special components requirements? High wattage resistors, etc... Thanks
 

Offline Jay_Diddy_BTopic starter

  • Super Contributor
  • ***
  • Posts: 2731
  • Country: ca
Re: Dynamic Electronic Load Project
« Reply #105 on: August 27, 2018, 02:48:58 am »
T1d,

So, is it okay to release the KiCad File?

You can do whatever you want. My recommendation is that you wait until you have finished and that you know that it works properly.

I have released schematic in the past, that I haven't built but I have marked them as such.

Hi,
I am going to share the design and construction of an ESR Meter adapter design and construction. The plan is to end up with a design that is similar in appearance to Dave's ucurrent that will allow a DMM to be used as an ESR meter. At this point in time I have not built the circuit.

The requirements are:


Snip ...

Jay_Diddy_B

I crossed out the warning after the circuit was built and tested.

You may want to swap the op-amps around during layout, to get a nice design.

It would be courteous to reference this thread on a schematics and board artworks that you release.

example:



My original artwork is shown in this post:

https://www.eevblog.com/forum/projects/dynamic-electronic-load-project/msg630287/#msg630287

Regards,

Jay_Diddy_B
 

Offline Jay_Diddy_BTopic starter

  • Super Contributor
  • ***
  • Posts: 2731
  • Country: ca
Re: Dynamic Electronic Load Project
« Reply #106 on: August 27, 2018, 02:53:20 am »
I know that the shunt resistors need to be 1%, IIRC. Are there any other special components requirements? High wattage resistors, etc... Thanks

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 should be 100V 1210 size.

Jay_Diddy_B
 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #107 on: August 27, 2018, 03:09:40 am »
Thank you!
 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #108 on: August 27, 2018, 03:33:53 am »
I have released schematic in the past, that I haven't built but I have marked them as such.
This is what I have/am intended to do. I just would have more confidence, in my work, if there was a consensus that it is correct. Not as to design operations, but as to circuit completeness and correctness. My desire is to contribute to the DIY community, by helping with creating a KiCad file, which should have wide utility. I don't feel any obligation, to warrant the design... nor should you, given open source nature, of this thread.
It would be courteous to reference this thread on a schematics and board artworks that you release.
Yes, I have remembered to do that. The schematic already has your name/handle credit. I will add the link info. My board layout already has both, but I really hadn't intended to release it, because it is tweaked, to my purposes. But, if someone wants it, I would share it, readily...
 

Offline JS

  • Frequent Contributor
  • **
  • Posts: 947
  • Country: ar
Re: Dynamic Electronic Load Project
« Reply #109 on: August 27, 2018, 04:02:45 am »
I have released schematic in the past, that I haven't built but I have marked them as such.
This is what I have/am intended to do. I just would have more confidence, in my work, if there was a consensus that it is correct. Not as to design operations, but as to circuit completeness and correctness. My desire is to contribute to the DIY community, by helping with creating a KiCad file, which should have wide utility. I don't feel any obligation, to warrant the design... nor should you, given open source nature, of this thread.
It would be courteous to reference this thread on a schematics and board artworks that you release.
Yes, I have remembered to do that. The schematic already has your name/handle credit. I will add the link info. My board layout already has both, but I really hadn't intended to release it, because it is tweaked, to my purposes. But, if someone wants it, I would share it, readily...
  If I were to build one of this which I'd probably like to, I'd include, as I did in mine, a thermal shout down. It's just matter of placing a LM35 on the heatsink and a comparator with some hysteresis shouting the thing down for a certain reference voltage. That makes it much more robust if something goes wrong I you don't catch in on time, as you are centered on other parts of the test other than the dummy load surviving it, like the DUT.

JS
If I don't know how it works, I prefer not to turn it on.
 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #110 on: August 27, 2018, 10:55:56 am »
Latest Dual Model schematic... I think I just added some notes...

« Last Edit: August 27, 2018, 11:03:11 am by t1d »
 

Offline Mihkel

  • Newbie
  • Posts: 5
  • Country: ee
Re: Dynamic Electronic Load Project
« Reply #111 on: August 27, 2018, 01:19:23 pm »
There is one important connection missing, between D1 cathode and V1 input.
 
The following users thanked this post: t1d

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #112 on: August 28, 2018, 12:29:38 am »
There is one important connection missing, between D1 cathode and V1 input.
Excellent catch, Mihkel.

It was easy, to process, quickly. I think I will post the KiCad files, tomorrow night. It would be great, if everybody would give the schematics one more look. Please and thank you...

You will recall, that I also made the schematic for the Single Supply model. It was only made, to the specs, of its model. That means that it does not have all the bells and whistles, that we put into the Dual Model. But, the user is welcome to finish it, as they like.

Jay, speaking of the Single Supply model, it was spec'd with just one 51 Ohm resistor, going to the Meter Output. Should it be one 100 ohm resistor, for each of the two MOSFETs?



« Last Edit: August 28, 2018, 12:42:59 am by t1d »
 

Offline Jay_Diddy_BTopic starter

  • Super Contributor
  • ***
  • Posts: 2731
  • Country: ca
Re: Dynamic Electronic Load Project
« Reply #113 on: August 28, 2018, 02:11:41 am »
Hi,

Here are some more corrections.

On the single supply version, you have the current monitor on the Drain of the MOSFET it should be the Source:



On the double supply version, the scaling factor is wrong. You have 8 x 0.2 \$\Omega\$ resistors in parallel so the scaling is 25mV / A:



Regards,

Jay_Diddy_B

 

Offline Jay_Diddy_BTopic starter

  • Super Contributor
  • ***
  • Posts: 2731
  • Country: ca
Re: Dynamic Electronic Load Project
« Reply #114 on: August 28, 2018, 02:33:54 am »
Hi,

Here are some comments on the input connector:



The schematic shows the part as conn_0.1x2, which suggest this type of connector:






The current rating of the connector is determined by the size of the wire you can attach to the mating part. This is limited to 22 awg (0.32 mm2) which is about 1A.

I would use something else.

Regards,

Jay_Diddy_B

« Last Edit: August 28, 2018, 02:35:38 am by Jay_Diddy_B »
 

Offline Jay_Diddy_BTopic starter

  • Super Contributor
  • ***
  • Posts: 2731
  • Country: ca
Re: Dynamic Electronic Load Project
« Reply #115 on: August 28, 2018, 02:46:48 am »
T1d,

You need to sort out the op-amp pin numbers.

In an earlier message you had decided to use the LT1013 op-amp with the non-standard pin connections:



But you are showing the, standard pinout, quad op-amp on the schematic:




Regards,

Jay_Diddy_B
 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #116 on: August 28, 2018, 03:20:17 am »
Good points, Jay.

On the double supply version, the scaling factor is wrong. You have 8 x 0.2 \$\Omega\$ resistors in parallel so the scaling is 25mV / A:
Actually, there are 5 pairs of resistors, at 0.2. I included five MOSFETS. I just replicated the MOSFET nodes, from the simulation circuit. I don't know how to do the math, to get 50 \$\Omega\$, but, if you want me to use it as a learning exercise and correct it, I would be glad to do that. We probably need to add a note, to the schematic, about adjusting the resistor values, based on the number of MOSFETs.

Here are some comments on the input connector: The schematic shows the part as conn_0.1x2, which suggest this type of connector: The current rating of the connector is determined by the size of the wire you can attach to the mating part. This is limited to 22 awg (0.32 mm2) which is about 1A. I would use something else.
One of the great advantages of KiCad, is that the schematic symbol does not dictate the board component. This is a good example. The schematic specifies what I thought to be a generic connector, of any type, having two pins. For the unit I will be building, I will be using banana jacks. I will assign the banana jack footprint to the generic two-pin connector symbol, with the component assignment function. But, not everyone may want banana jacks.

Because you have made me aware that this particular two-pin connector symbol actually specifies the connector you showed, I will see if there is not a banana-style connector symbol. Or, would you think some other type connector would be better?
« Last Edit: August 28, 2018, 03:27:58 am by t1d »
 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #117 on: August 28, 2018, 04:19:22 am »
I searched for a banana jack symbol, until I realized how long I had been at it... There's a hour, I'm not getting back. This is the closest symbol I could find. It's easy enough to create the symbol, in KiCad, if this symbol (doughnut) will do. Thoughts?



EDIT: Here's my KiCad version. Even if we don't use it, for this project, I need it, for my general library of symbols.
« Last Edit: August 28, 2018, 05:28:15 am by t1d »
 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #118 on: August 28, 2018, 06:47:03 am »
This is the correction, to the Single Supply model. The reference numbers will be R5 and R6.

 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #119 on: August 28, 2018, 08:41:38 am »
T1d,

You need to sort out the op-amp pin numbers.

In an earlier message you had decided to use the LT1013 op-amp with the non-standard pin connections:



But you are showing the, standard pinout, quad op-amp on the schematic:




Regards,

Jay_Diddy_B
 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #120 on: August 28, 2018, 09:01:09 am »
T1d,

You need to sort out the op-amp pin numbers.

In an earlier message you had decided to use the LT1013 op-amp with the non-standard pin connections:



But you are showing the, standard pinout, quad op-amp on the schematic:




Regards,

Jay_Diddy_B
Doh! You are exactly correct. In the beginning, I was trying to decide whether to use quads, or duals. Looking at the device specifications, between the LT1013 and the LT1014, they are the same, IIRC... (except for the LT1013CDR, as previously discussed...) So, my thinking was that quads save real estate and I put in the quad symbol. But, as I went back and labeled the components from your model, I dropped the ball and assigned LT1013, as the device reference.

So, we have a choice, here... I can just change the labeling to "LT1014." That's the easiest solution. Or, if you prefer the dual, I don't mind making the pin changes.
 

Online Kean

  • Supporter
  • ****
  • Posts: 2050
  • Country: au
  • Embedded systems & IT consultant
    • Kean Electronics
Re: Dynamic Electronic Load Project
« Reply #121 on: August 28, 2018, 11:49:14 am »
Another minor error - the 100R resistor for the monitor output (near R21 labelled R?) connects to ground instead of the junction of R21 and M2 source pin.

This is the correction, to the Single Supply model. The reference numbers will be R5 and R6.


 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #122 on: August 28, 2018, 02:31:25 pm »
Another minor error - the 100R resistor for the monitor output (near R21 labelled R?) connects to ground instead of the junction of R21 and M2 source pin.
Nice one, Kean! The two unnumbered resistors have been assigned as R5 and R6. Here's your fix:

 

Offline t1d

  • Super Contributor
  • ***
  • Posts: 1212
  • Country: us
Re: Dynamic Electronic Load Project
« Reply #123 on: August 28, 2018, 02:45:29 pm »
I went ahead and built the SOIC-8 pinout, for the LT1013 symbol. Making the needed Dual-or-Quad Op Amp change will be easy. Just let me know, which way to go. If we go with the Quad LT1014, I will try to remember to include the LT1013 symbol, in the files I post, so individuals can easily change the design.

The Quad LT1014 has a common footprint to the TL074. So, if an individual wants to use the LT1014, they just place the TL074 and change its name.

 

Offline Kleinstein

  • Super Contributor
  • ***
  • Posts: 14067
  • Country: de
Re: Dynamic Electronic Load Project
« Reply #124 on: August 28, 2018, 03:00:46 pm »
For the FET drivers, there is likely not much space to save from using a quad version (e.g. LT1014), because the power MOSFETs need so distance in between anyway. So it is 2 extra pins versus longer tracks. The square wave generator part does not need a precision OP - here an LM358 / 741 could be good enough. It's mainly the output drivers that need to be precision due to the low voltage at the shunts.

For the MOSFET choice, I would be careful with IRFZ20: The DS (from vishay) shows an DC FBSOA, but it is a reasonable modern switching MOSFETs for just 50 V. The FBSOA might be just calculated from transient thermal response and not include possible thermal instability. 

The more sensible alternative would be to consider an TO247 case type like IRFP250. These could handle more power in a single chip and thus less channels needed. The higher voltage rating and thus low trans-conductance also helps with thermal stability.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf