Yes.... Another Dummy Load - Page 1
Forum section: electronics / projects

author: wigman27
author_rank: Regular Contributor
timestamp: August 26, 2013, 10:07:27 am
content: Hey again,Yes, it is another dummy load I am having an op amp issue and im not really sure whats causing it.I am controlling this dummy load with a micro to give my constant current, power and resistance. I am controlling it with a 12 bit DAC using a 4.096V reference to give 1mA steps up to 4 Amps, I may choose to go to 8 Amps at lower voltages, I haven't fully decided yet. With that in mind I wanted to use a 0.1 Ohm load resistor to save heat at higher currents and losses at lower voltages.This is my first attemptU2 was to multiply the feedback voltage to U1 by 10 so 4.096V from the DAC would give me 4.096A still. However the circuit oscillated terribly, it worked perfectly fine during the initial testing but it started to oscillate for no apparent reason. Is it something to do with the two op amps like that? should I not do that? I intend on using the LM324 in the real circuit but the LM1014 was easier to model with.I have fixed it in my second attempt, I have removed U2 and put a voltage divider from the DAC instead and it works really well.I am just curious what the reason for the oscillation was?ThanksLee

author: Rerouter
author_rank: Super Contributor
timestamp: August 26, 2013, 11:04:47 am
content: One day someone will search the forum before posting, today is not that day...add 100 ohm between the op amp output and the mosfet gate, and 1n between the op amp output and the inverting input, this will slow down the loop and make the op amp more happy with driving a capacitive load,

author: wigman27
author_rank: Regular Contributor
timestamp: August 26, 2013, 11:17:56 am
content: Hi Re router,I did search quite a bit before posting, obviously not enough, I'm really sorry about that. I am an admin on another forum and understand how annoying that is.I appreciate you answering me anywayThanksLee

author: toli
author_rank: Frequent Contributor
timestamp: August 26, 2013, 08:21:37 pm
content: Have a look here:https://www.eevblog.com/forum/projects/yet-another-constant-current-load/The solution I've offered starts here:https://www.eevblog.com/forum/projects/yet-another-constant-current-load/msg146592/#msg146592I've also explained to him what was causing it.In the schematic you've shown, other than the pole at the output of U1 (which might in some occasions be high enough, it really depends on the OPamp and transistor parameters) there's another pole within the loop caused by U2. So you should do what was offered in the link I gave you, add a resistor to the gate of the MOSFET, add a capacitor from output to inverting input of U1, and add another resistor from inverting input of U1 to the output of U2 (or else you'll need a really large capacitor).This will keep the DC current at the value you want (as the parts we've added won't change the circuit in DC due to the high input impedance of the MOSFET and U1 at these low frequencies), but at high frequencies where poles start piling through the loop, we've offered another path using the new capacitor, which will keep U1 stable. The resistors will help us isolate this alternate path from the rest of the loop.

author: wigman27
author_rank: Regular Contributor
timestamp: August 28, 2013, 06:53:02 am
content: Quote from: toli on August 26, 2013, 08:21:37 pmHi Toli :-)That worked perfectly! I ended up using 100R resistors and a 100n cap and it seems very stable.I think I will go for the second option using a voltage divider. For two main reasons, one, its one less op amp, and two, the 1st option won't let me get down to the lower currents without using a split supply, as the lt1014 will only go down to 7mV output swing and then that's amplified to 70mV at the inverting input of U1.It obviously doesn't matter that the output of U1 can't get to 0v as the threshold voltage of the MOSFET is 1.7vCan you see any other issue with using the second option? I will add the 100R and try a 10n to start with.Thanks again for your help!

author: toli
author_rank: Frequent Contributor
timestamp: August 28, 2013, 07:09:59 am
content: The second option seems identical to what was discussed in the link I gave you. Its really a simple circuit. Other than doing what I've explained for stability, I don't think there's much to go wrong with this very simple circuit.BTW, did you add another resistor from the inverting input of U1 to the output of U2 in the first version/the current sense resistor in the second version?It will probably be a must for the second version. In the first version the output impedance at high frequencies can be 10's-100's of ohms (I'm too lazy to open the datasheet of the opamp to check) so you might get away without it, but in the second version the output impedance is 0.1R so unless you add this resistor the 100n cap is going to be too little and it might also load the output of U1 too much.

author: wigman27
author_rank: Regular Contributor
timestamp: August 28, 2013, 08:09:36 am
content: Quote from: toli on August 28, 2013, 07:09:59 amYep I sure did :-) everything worked well.QuoteI will have a good play and post the final schematic if that's ok :-)Thanks again for your help!

author: toli
author_rank: Frequent Contributor
timestamp: August 28, 2013, 08:18:48 am
content: My pleasureBTW, I'd add a capacitor in parallel with the voltage divider just to lower the noise U1 will see at its input. It'll slow the response slightly, but its a DC load so who cares?!

author: wigman27
author_rank: Regular Contributor
timestamp: August 29, 2013, 01:43:53 am
content: Quote from: toli on August 28, 2013, 08:18:48 amWill do, would 100n be too much capacitance for that?Also I'm thinking of dropping the sense resistor to 0.01 ohms instead of .1 and change the divider to 100. Would that cause issues being that lower sense voltages do you think? Being in the noise?At the moment it works quite well down to 2mA so that would be down to 20uV on the op amp inputs. Not sure if the lm358 will do that well. What's your thoughts?Lee

author: toli
author_rank: Frequent Contributor
timestamp: August 29, 2013, 05:06:29 am
content: 100n should work, there's no such thing as too much in this location as its a DC load.Regarding the voltage drop, I'd advice against it. if you have 4.096V/10=0.4096V at the moment, there's very little gain in minimum operating voltage by dropping it lower. I'd leave it at the 0.1R value.

author: rdl
author_rank: Super Contributor
timestamp: August 29, 2013, 08:47:53 pm
content: I actually built one of these "dummy loads" last weekend. It doesn't seem to work right.I followed the exact schematic in the EEVblog episode 102 with only two additions, the 1 nf cap across the output and inverting input of the second op amp, and a 100 ohm resistor between the output and the FET.I hooked it up to a power supply and I could adjust the current loading but every time I changed the voltage on the power supply the current would change also.I hooked my scope up to the output of the second op amp and it was a sort of sawtooth waveform, about 1 to 2 volts and around 200kHz to 300kHZ. This should be a DC voltage pretty much right? Relatively flat without a lot of noise?I think I'm going to replace the resistor with a pot and maybe add a pot between the FET source and op amp inverting input. Then hook up a cap substitution box and see what it really takes to make it work correctly.

author: TerminalJack505
author_rank: Super Contributor
timestamp: August 29, 2013, 09:08:20 pm
content: Quote from: rdl on August 29, 2013, 08:47:53 pmThere are quite a few threads regarding Dave's dummy load on the forum. I think if you follow Toli's advice in this thread you can get it working.Here are a couple post that have schematics of circuits that are known to work:Jay_Diddy_B'sTerminal Jack's

author: rdl
author_rank: Super Contributor
timestamp: August 29, 2013, 09:44:08 pm
content: I did search, dummy load returned about 3 pages of results. Around a third were actually about Dave's circuit. I should have narrowed the search a little more I guess.As I said, I built Dave's original circuit exactly except for the cap and resistor, both of which were recommended additions in many of the posts I read. However, there is a lot of variation in the values recommended for those parts, as well as in the actual op amps and FETS that people use. I used the same MTP3055VL as Dave and an LM358 (dual version of the LM324). Didn't work. Don't worry, I will figure it out eventually. Maybe it's my circuit layout, I built it on perfboard.

author: TerminalJack505
author_rank: Super Contributor
timestamp: August 29, 2013, 10:12:21 pm
content: It sounds like you are missing a resistor between the 1R current sense resistor and the op amp's inverting input. This was key for stability when I built the circuit.

author: rdl
author_rank: Super Contributor
timestamp: August 29, 2013, 11:09:52 pm
content: No, I didn't have that resistor. I just now cut that wire and clipped in a 2K pot, but it doesn't seem to make a lot of difference. The magnitude of the waveform and the frequency change somewhat as I rotate the pot, but I'm still not getting anything close to DC out from the op amp.I'm thinking the 1 nf cap across the op amp's output and inverting input is too small (I see you have used 10 nf). Tonight or maybe in the morning I'll solder on some wires so I can connect my cap substitution box there. Should I replace the 100R on the FET gate with a some kind of pot also?I attached my pcb layout. It's built on pad per hole perf board. All wiring is on the bottom, bare 24 gauge solid wire in straight lines point to point (except the thicker lines are 18 gauge solid).Iwillget this to work, I've spent too much time on it to give up now, besides it might actually be usefulThanks for your advice.

author: TerminalJack505
author_rank: Super Contributor
timestamp: August 29, 2013, 11:25:15 pm
content: Yeah, there will be some magic combination that makes it work so stick with it.If you leave the size of the resistor between the output and the gate at 100R then the resistor between the current sense resistor and the non-inverting input will likely have to be in the range of 10k. Your circuit is similar to Jay_Diddy_B's and that's what he used. (He has a 10k from current sense to non-inverting input, a 220R on the MOSFET gate and a 470p compensation cap.)

author: wigman27
author_rank: Regular Contributor
timestamp: September 08, 2013, 10:58:34 am
content: Hey againSorry for the delay.. Work got in the way of electronics!! How RUDE!Ok, So I have come up with a circuit that was very stable across all ranges, all currents from 2mA to 8A all voltages from 1.5V to 24V using the LT1014 which I thought was reasonably close "replacement" to the LM324 which I planning on using in my final circuit. It worked exactly as you would expect.I had reached a stage I was happy with so I thought I would find an LM324 model to try, just to be sure, when I replaced the LT1014 with the LM324 the circuit went crazy!It didn't oscillate but the MOSFET was very slow to respond at low currents and huge overshoots at high current settings then it would finally settle. I wasn't able to get the LM324 anywhere near the same low current outputs that I was getting the LT1014 down to. I'm guessing it could be a few things, does it sound like any of these?Dodgey LM324 subcktThe LM324 is not as precise as the LT1014 and not able to sense the lower voltages at the 0.1ohm resistor R1It has something to do with the phase shift I have done for the LT1014 isn't satisfactory (or just a different requirement) to the values I should be using for the LM324?I would really appreciate some help as to what may be going on. I have attached a zip of the folder as there are two library's and also I haven't worked out how to save the .asc file to text nicely as yet.Thanks for your help!Lee

author: Rerouter
author_rank: Super Contributor
timestamp: September 08, 2013, 11:28:21 am
content: lets rule out the basics,common mode input range includes ground, checkoutput can get close to ground, checksink and source current are not the same, (may not be pulling down fast enough at current time constant)figure 13 is interesting,http://www.ti.com/lit/ds/symlink/lm124-n.pdfequally is common mode rejection is about 40db worse than the LT1014,

author: Kevin.D
author_rank: Frequent Contributor
timestamp: September 08, 2013, 12:16:37 pm
content: Yes the lm324 model your using is very broken I would say . I tried your circuit with using two lm324 spice models I have LM324/NS and LM324/ST and both work ok in your circuit .Having said that you are still not using very good values in your circuit to achieve a good fast but stable control loop when using lm324 and it's clones.. I would put a bigger resistor on the gate ~ around 470 ohms . And decrease c2 to around ~ 22n and decrease R5 to ~1K . This should give you good stability for most load conditions without slowing the feedback loop to much .

author: wigman27
author_rank: Regular Contributor
timestamp: September 08, 2013, 12:29:39 pm
content: That's good!! Thanks very much guys.Quote from: Kevin.D on September 08, 2013, 12:16:37 pmI will try these new resistor and cap values out. Can I ask, how did you come up with these values? Is it experience or is there a good way of working them out? I did do a bit of reading initially on phase shift angles but still havent found a way to work it out thy doesnt require a doctorate in all things electrical... I'm just asking so I will know for next time :-)Would you mind sending me a link to the models you have?Thanks again :-)Lee

author: TerminalJack505
author_rank: Super Contributor
timestamp: September 08, 2013, 12:39:07 pm
content: So far as I can tell you have two problems.One, your bandwidth is about 600Hz. I changed things to what's shown in the attachment a got a lot more bandwidth.The other problem is voltage offset. By using a 0.1R resistor you're getting a gain of 10x as well as seeing 10x worse offset. Which could account for up to 70mA of error on the output with the LM324's worse-case offset of 7mV.

author: rdl
author_rank: Super Contributor
timestamp: September 08, 2013, 01:08:43 pm
content: I built the exact circuit as shown in EEVblog #102 and it oscillates like crazy. I built it again adding the resistor between the op amp and the FET and the cap across the op amp output and inverting input (C2 and R4 in your circuit) and it still oscillated (see my previous posts in this thread). If I didn't have an oscilloscope I probably never would have been able to fix this circuit.I replaced C2 with an IET Labs capacitor substituter and replaced R4 with a 2K pot. Then I added a 5K pot between the FET source and the op amp's inverting input (R5 on your schematic). 5K turned out to be way too large, I had to change it to 500 ohms.Based on my tests, using LM358 and MTP3055VL as in the original circuit:R4 is required to prevent bad oscillation when the load voltage is outside 3 to 8 volts range.I was able to stabilize the circuit with R4 only, but it required a very large value (over 47K).Around 100 - 150 ohms worked fine here when used with C2 and R5.C2 needed to be 110n minimum, going higher didn't seem to hurt, so I settled on 330n just to be safe.R5 was where it got strange. The required value was between about 5 ohms and 50 ohms only.Anything outside this range an the circuit would oscillate badly, without the oscilloscope, I probably would never have figured this out.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 08, 2013, 01:31:25 pm
content: Hi group,I recently posted a design for a dynamic load. This thread can be found here:https://www.eevblog.com/forum/projects/dynamic-electronic-load-project/msg288313/#msg288313The design shows how to use more than one MOSFET to share the dissipation.It also shows how to make a pulsed load that can be used for doing transient load test on power supplies.Regards,Jay_Diddy_B

author: Kevin.D
author_rank: Frequent Contributor
timestamp: September 08, 2013, 02:12:13 pm
content: The two ltspice models i use you can find here .http://ltwiki.org/?title=Components_Library_and_Circuitsjust click on the 7.-opamps . and you will find lm324/ns model there .on this same page both the lm324/ST and lm324/ns are in the "A Large LTspice Folder from Bordodynov" in the "extra" folders of that download . These are what I used .On how did I came up with these values , It was from both a bit of experience and from looking at the bode plots of these circuits . If you want to do the bode plot of your circuit try the "loopgain2" method you will find in the examples directory of lt spice .Bode plots are fairly easy to do (in spice anyway ) but youl need to do a bit of reading and practice to interpret them and use them (but basically it's phase shift at the 0db gain crossover point that's the important bit ) .What your trying to do here is get a stable but as fast control loop as you can ,so this means adding as little compensation as you can get away and still be stable .(it's very easy to stabilize any feedback control loop just by keep adding more compensation and reducing it's bandwith to lower values but then you have reduced it's abilility to react fast to any changes which is the whole point of the feedback loop in the first place,.).An easy way for most hobyiest and beginers to check control loop stabilty with out having to do Bode plots(and it works for 99% of the time) is to just do a step load response and you can get an good indication of the phase margin ( stabilty) that way . the nice thing about this is that you dont need expensive equipment and to can do this in both Ltspice simulation and on the real circuit , you can then compare the results . (to do this in ltspice on your circuit just step the load voltage souce (V2) rapidly a few volts in your simulation and then plot the response across the current sense resistor (R1) ).you can then compare to chart like I have posted below to get the phase margin, the amount of overshoot/ringing indicates phase margin ,you aim for about ~ 60 deg margin for a optimized loop .(but you should also test under the worst working case senariou your likely to see to check is still stable (not oscilating but will have much reduced phase margin). :-that is with a resistive load in the Drain of Fet for Electronic load type circuits like yours ).Or you could of course avoid all the above and just copy what everyone else does .It's up to youAnyway It's sunday ,so my day of rest so enough typing for me today.Good luck .

author: wigman27
author_rank: Regular Contributor
timestamp: September 09, 2013, 09:39:00 am
content: Quote from: TerminalJack505 on September 08, 2013, 12:39:07 pmHi TerminalJack505,Thanks for your replyMy original circuit did have an offset problem as it was using a x10 gain op amp picking up the voltage drop across the 0.1ohm resistor. However with this circuit I don't have any gain in the op amp and offset isn't really a problem a the threshold voltage of the MOSFET is around 1.7v so 7mV offset hopefully won't worry me too much.QuoteThanks mate! I will definitely check this out, I will have to do some research on the right values to use, I will start with the values Kevin.D and you have suggested as a start.QuoteI saw that! it looks very nice!! thank you.QuoteThats way too easy! sometime I just wish I could do that... but no, I have to know EXACTLY how it works or its not good enough for me..Thanks for taking time on Sunday to answer these questions.I will let you all know how I go.Lee

author: wigman27
author_rank: Regular Contributor
timestamp: September 09, 2013, 10:43:40 am
content: Well,I have replaced the LM324 with the Bordodynov library one followed Kevin.D's values exactly and stepped the DAC voltages and load voltages and its working perfectlyI have also tidied up the spice schematic so its a little more readable and lets go with that I thinkThank you all VERY much!Lee

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 09, 2013, 11:56:12 am
content: Lee,You should add a damping circuit of 2.2uF and 2.2 ohms from the MOSFET drain to ground.If you add some inductance, 1-10uH between the MOSFET source and the Power being tested, the circuit might oscillate.This inductance is to represent the inductance of your test leads.Jay_Diddy_B

author: TerminalJack505
author_rank: Super Contributor
timestamp: September 09, 2013, 02:58:09 pm
content: Quote from: wigman27 on September 09, 2013, 09:39:00 amYou still have a gain of 10. 1V on the input leads to 10A of current on the output. That's a transconductance gain of 10.Note how the op amp's voltage offset is multiplied by this gain in my attachment.(I had to use a negative rail to avoid the fact the LM324 can't quite get down to 0V with a single supply which, otherwise, makes the offset seem worse than it really is.)

author: wigman27
author_rank: Regular Contributor
timestamp: September 11, 2013, 11:27:29 am
content: Quote from: Jay_Diddy_B on September 09, 2013, 11:56:12 amWhat does this do? I see that your schematic has the same values also, is it a fairly standard practice?Lee

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: September 11, 2013, 09:48:47 pm
content: Lee,You asked, so let me explain.When I was developing my Dynamic load I was trying to get high bandwidth for doing transient load tests. I did my control loop without considering the characteristics of the test leads that are used to connect the power supply to the load.When I tried the load I found the current oscillated at around 200kHz.So I thought may be the inductance of the leads going between the power supply and the load were causing problems.I estimate that the inductance is between 1 and 5uH.I can make a small signal model:These are the results, the current splits between the source and the damping network depending on the frequency.Without the damping network, the source impedance rises.Adding the damping network let me get a high bandwidth dynamic load. The damping network is really a function of the lead inductance and resistance.Jay_Diddy_B

author: wigman27
author_rank: Regular Contributor
timestamp: September 12, 2013, 10:26:49 am
content: Hi again!That makes perfect sense, thanks Jay_Diddy_BAs a matter of interest to others, Neilm postedthisdocument in another topic. It explains what happens to op-amps when driving capacitive loads perfectly!Thanks again everyone!Lee

author: wigman27
author_rank: Regular Contributor
timestamp: September 21, 2013, 11:02:58 am
content: Hi,I have been having a play with the power supply for the control circuit and I would like to incorporate the 5V auto selector type system from the Arduino Leonardo to swap between VIN and VUSB. (schematic attached)As I will be powering the circuit directly from 5V adapter, I will not be running the supply through a regulator and then "isolating" VIN from VCC 5v and I don't have 3.3v, so the Arduino circuit won't work.I have had a play with a few things, the second attachment below is using a Schottky diode to "isolate" VIN from VCC which works but I really don't want the 300mV (or more) volt drop across the Schottky.So the Third attachment is an Oring circuit that I have played with but seeing as though the voltages are very similar, both MOSFETs work in parallel instead of isolating the USB voltage.I know the OP amps aren't setup yet for driving capacitive loads but I am just trying it out at this stageDoes anyone have any other ideas I could try?

author: TerminalJack505
author_rank: Super Contributor
timestamp: September 21, 2013, 10:36:52 pm
content: You need to give one of the supplies priority. You might look at the circuit inthis postfor some ideas.

author: wigman27
author_rank: Regular Contributor
timestamp: September 22, 2013, 11:51:46 am
content: Thanks TerminalJack505I had actually seen that post in my original searching for an answer but I didn't really see anything without a Schottky or your version, which to be honest, I am having a little trouble working out exactly how it works.My priority supply is defiantly the VIN 5V Jack so I think I will either bite the bullet and go with a Schottky, or use a relay. the relay I was thinking is attached below, very similar to the one suggest in that other post.The main reason I don't want to use a Schottky in series with VIN is because the op amp I am using to drive the MOSFET needs to go up to about 3.2V to drive 8A through the FET so I don't really want to drop VCC any more than I have to.I could use 9V power on the opamps and a 5V reg for the rest of the circuitry but I really want to use 5V USB as a secondary supply. There are many many ways to skin a cat but I think these two may be the best for this purpose.What would be your pick for this?

author: TerminalJack505
author_rank: Super Contributor
timestamp: September 22, 2013, 12:51:59 pm
content: The relay seems like a good solution. I don't know if it would work properly for "hot switching" (or whatever the term is.)So far as how my circuit works, the two leftmost comparators are acting like a window comparator with a little feedback via R4 for a Schmitt trigger type of action. They sense the primary voltage via R5 and R6 and output a low voltage only if the primary is between the two voltages set by R1, R2, R9 and R3 (I just picked an arbitrary low and high voltage.)The diodes on the first two comparator's outputs allow the outputs to be tied together so that they work in a wired-AND fashion. This output is feed to the next stage which turns on either the primary or secondary, as appropriate.Note that the MOSFETs are back-to-back to prevent the body diodes from conducting. If this isn't done and just a single MOSFET is used then you risk having one supply force current into the other OR (if the body diodes are the other way) having the supply with the higher voltage do all the work, despite which one is switched on. (The body diodes would just act as OR-ing diodes in that case.)

author: wigman27
author_rank: Regular Contributor
timestamp: September 24, 2013, 10:02:12 am
content: Quote from: Rerouter on August 26, 2013, 11:04:47 amHey Rerouter,Today is that day!! I just needed an answer, searched the forum and found the answer!! thought you may be happy to hear it!Happy TuesdayLee

author: wigman27
author_rank: Regular Contributor
timestamp: October 07, 2013, 09:47:05 am
content: Hey AllI have finally got a schematic together, I haven't fully tested every component together yet so it may change without notice.Some feedback would be awesome!Thanks Lee

author: Harvs
author_rank: Super Contributor
timestamp: October 07, 2013, 10:22:34 am
content: For the fan, I would be inclind to just use a regular PC fac (which maybe that is?), as they include their own driver circuitry. Then you just send it a 25kHz PWM signal to set the speed, no need for additional circuitry.I would encourage you to provide a bias supply for the opamps, check out the jelly bean 7660. For some reason people seem to be shying away from this, but it'll add about $1 worth of parts to add a cap voltage inverter and it'll mean you can actually operate down to 0A. You can also then add a small negative offset to the DAC output so it can go down to zero as well, because it'll only go to several mV above zero at the moment.

author: wigman27
author_rank: Regular Contributor
timestamp: December 20, 2013, 12:50:33 am
content: Well I have finally finished my first PCB design!!I'm pretty happy with it, I would love to hear suggestions on stuff I could do better and differentlyI have attached the top and bottom layers separately.Thanks again ;-)

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: December 20, 2013, 01:39:29 am
content: Hi,You might want to consider a larger connector in the PL1 position. The connector you have looks a little small for your maximum load current.Jay_Diddy_B

author: wigman27
author_rank: Regular Contributor
timestamp: December 20, 2013, 01:46:36 am
content: Hey mate,Thanks :-) as I was designing the board I had the same thought, my max load is 8a and the trace width is 5mm. Molex do a connector that will do 10a with the 100thou pin pitch. So I decided to run with that for now and may go bigger for rev b if it needs it.What do you think?

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: December 20, 2013, 04:27:08 am
content: Hi,I think 8A on a 0.1" connector is a stretch. You can always solder some wires directly to the tracks if it becomes a problem. I did a quick check on Digikey and I found that the 0.025" square post were 4A max. The mating connector was sized for 22 awg max.On the 0.1" connectors they are specifying 15m Ohms. At 8A this 960mW per pinThe larger 0.156" center connectors with a 0.045" square post are specified at 7A and will take an 18 awg wire.Jay_Diddy_B

author: wigman27
author_rank: Regular Contributor
timestamp: December 20, 2013, 05:50:15 am
content: Yes, very good point!!Thanks, I will go with a soldered wire this time and fix it in b. that will make it easier to get the tracks in.Where I have put the larger track into the MOSFET at the top of the board, is that the best way to shrink them down to fit the pin pitch? Have you got any examples of how better to do it if not?Thanks again :-)

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: December 20, 2013, 12:31:33 pm
content: Hi,In the Dynamic Load Project:https://www.eevblog.com/forum/projects/dynamic-electronic-load-project/msg288313/#msg288313I used both sides of the board for the MOSFET connections. I had the Drain connections on the same side as the MOSFET and the Source connections on the other side. If you do not use an insulated device or a silpad, the heatsink is at the Drain voltage.Here are the pictures:Jay_Diddy_B

author: wigman27
author_rank: Regular Contributor
timestamp: December 30, 2013, 12:31:40 am
content: Well the PCB is here!!!I cant wait to try it out!!

author: wigman27
author_rank: Regular Contributor
timestamp: July 01, 2014, 11:24:54 am
content: Yes, It has been a very long time in the making.. but here is the finished version 1 productI have learned a lot!! which is the main reason for doing it!! But all in all it works as designed (after a number of newbie issues).I had a few footprint issues which is my fault because I check nearly everyone except the processor!! dir!!Murphy strikes again and I stuffed up...There is still a bit more refining of the software and hardware but im pretty happy with my first real electronics design and build!On to version 2! try and implement isolation plus a number of other thingsA big thanks to everyone who helped!Lee

author: wigman27
author_rank: Regular Contributor
timestamp: August 12, 2014, 12:06:40 pm
content: Version 2 is now finished!To see the finished product I have started a thread in the open source hardware section that shows a link to my instructable and videos that I have donehttps://www.eevblog.com/forum/oshw/arduino-programmable-constant-current-power-resistance-load/A huge thank you to everyone that helped me with this! Most of all Dave that inspired me to do it in the first place!Thanks againLee