ESP32 Sensitive electronic load  - Page 1
Forum section: electronics / projects

author: Samy.Amer
author_rank: Newbie
timestamp: March 30, 2021, 02:39:05 pm
content: Hi,I am sorry if my question is related to other posts, If so please point it out to me.I am trying to make my own electronic load using ESP32, I am going to use either multiple IRFP260N or IXTK90N25L2 as the load mosfet. My question isI am using a 50 amp 75 mv shunt and planning to use a 12bit DAC for the control signal and the attached schematic for the circuite.As I am trying to enhance the control so I want to use an amplifier for the current measuring voltage signal (before the shunt).Is this circuite correct or I have to add more elements.Please note that my specialization is not electronics

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 31, 2021, 10:01:06 am
content: Get rid of R3-C1 (I think it is not the best way to ensure stability). In general - it is ok as a concept. But the exact answer depends on the exact requirements (max. voltage, current, power)

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 31, 2021, 10:07:32 am
content: Here is an example of manually controlled electronic load (left side is a voltage control unit, right side is an electronic load itself):This circuit for 10 A rated current has R20, R21 of about 0.020..0.025 R each.

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 31, 2021, 10:14:28 am
content: Whether to use 75 mv 50A shunt or something else with higher resistance depends on a needed rated current. It is not easy (not cheap) to linear amplifire a 1.5 mV DCV. If you really need to use a 75mv 50A current shunt but not 0.010-0.050 R current shunt then you possibly need to implement a differential amplifier instead of a simple non-inverting one.

author: Samy.Amer
author_rank: Newbie
timestamp: March 31, 2021, 11:49:36 am
content: Thank you for your reply,Let me try to explain what I am looking for, I need to send the control signal from ESP32 the issue is that max sensing signal for 50 amp should be 75mV however after using 12 bit DAC the max accuracy will be 3.3v / 4096 = .8 mV so the smallest current segment that I can address will be (50 amp / 75 mv) * .8 = .533 amp.I am looking for better control even up to 10 m Amp so I thought about using an amplified signal for current sensing signal so I can utilize larger range of the control signal.Will that be possible? what should I add or remove to achieve my goal?My voltage ranges are:Vin up to 150vVctrl up to 3.3vmax current targeted 50 amp and by adding one more line in parallel I think I can achieve 100 amps

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 31, 2021, 01:41:29 pm
content: Quote from: Samy.Amer on March 31, 2021, 11:49:36 amOk, now with that specification we can work.QuoteWe can start from the point that a single IRFP260N can't withstand a 50A job at any voltage. And it is a bit hard for a single IXTK90N25L2 (I^2*R = 50A^2*0.033R = 82.5W).So, we have to divide a 50 A current into smaller parallel chains. As for me, I would use 10A max for each Mosfet max (for IRFP260N), so that gives 5 parallel chains at least (it can be more, up to ten). That means that a shunt can have a larger value (0.01 R at each Mosfet, for example).Anyway, such quite large currents much better to measure with a differential amplifier, which may have a gain of about 10 (+-, somewhere between 5 and 20..50). So, with a 10 A current and 0.01R shunt, we'll have 0.1VDC voltage across a shunt. Multiplied by 10 it is 1.0VDC - much easier to work with.You may use two 0.01R shunts in series, or a gain of 20, to have 2.0VDC at 10A current and 0.01R shunt (to have a good resolution).You may use one 0.01R shunt (for 10 A) at a gain of 30 you'll have 3.0VDC.You may use a 50A 75mV shunt too but for a common main ammeter.If you want to use 50A 75mV shunt as Mosfet's current sense then I would use two in series, which gives 150 mV (at 50ADC), or 75mV at 25ADC and a gain of 20.One TO247 case (IRFP260N) can withstand lasted dissipation of about 50-100 W of active power.One TO-264 (PLUS247) case (IXTK90N25L2) can withstand lasted dissipation of about 100-300 W of power lasted.It depends on cooling, of cause, and on an actual source-drain voltage.Both of them are good for a 150VDC rated load. Both are good ones for a linear mode (for an electronic load).You have to consider which exact Mosfet to use because they are in different leagues.If you chose IXTK90N25L2 you may need about 2 parallel Mosfets to handle with 50 A (as in my circuit example), and 4-5 cases for 100 A rated device.I'm not talking about a rated power now. This must be defined too.

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 31, 2021, 02:07:39 pm
content: Here is an example of how to parallel a lot of Mosfets (to work with a large currents or large dissipated power):

author: Samy.Amer
author_rank: Newbie
timestamp: March 31, 2021, 02:10:24 pm
content: Thank you so much,The max current is not a show stopper as I am planning to test the max power dissipation based on actual figures and to not exceed 75c temperature which will be controlled via temp controlled fan mounted on a big cpu heatsink. after proving that I can control the circuite with the current accuracy that I am looking for I can easily add parallel similar tracks.Most probably I will use the IXTK90N25L2 to decrease the no of tracks as I am hoping to be able to make this modular and add modules as needed.Currently I am in need to confirm what is the right circuite to achieve my goal before making it and burn some expensive components. (the IXTK90N25L2 cost $26 on moser and not available and from china it cost around $6 and takes month to reach me)

author: Vovk_Z
author_rank: Super Contributor
timestamp: March 31, 2021, 04:45:03 pm
content: It is fine to use IXTK90N25L2 for 50 ADC rated device. And it could be reasonable to use much cheaper IRFP260 for experiments.

author: Samy.Amer
author_rank: Newbie
timestamp: March 31, 2021, 05:42:15 pm
content: That is exactly what I have in mind.First I need to confirm if the overall circuit is correct so I need to make some modification based on the circuites you shared and come back to reconfirm.Really appreciate your help