Author Topic: DIY SCPI programmable dual channel bench PSU 0-50V/3A (now EEZ H24005)  (Read 296625 times)

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Offline Jon_Paul_Clarke

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Re: DIY programmable dual channel bench PSU 0-50V/3A
« Reply #225 on: January 18, 2016, 09:24:28 am »
Dude,
I love how you're documenting and showing this project for all to see. I think a lot of people are very interested in this project, not just for seeing this come to fruition but from a technical standpoint as well. This sort of thing is really the pinnacle of hobby electronics and it is teaching all of us about electronic design solutions. Thanks Heaps and keep up the good work!

Jon, Electronic Noob and All-round Annoyance
"It's not the 'juice!' It's a protein supplement!"
 

Online prasimix

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Blowing some air ...
« Reply #226 on: January 25, 2016, 09:58:50 am »
I spent some time over the weekend to address the topic about toroidal transformer (over)heating that is mentioned in some of the recent post. It seems that I reinvent the wheel, or actually the fan :). Situation with adding some forced air becomes much much better. Ok, that's against my initial wish that PSU shouldn't have such source of noise. For testing I simply opened the top cover and use hairdryer fan without heater switched on to just blow air over the transformer. A huge temperature drop (20oC and more) is achieved. I have to see how it will looks with smaller fan e.g. 60x60x25 mm mounted on rear panel. Of course some fan control circuit has to be added that fan is not working if load is small (in general below 2 A).
 

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Input protection
« Reply #227 on: February 04, 2016, 09:49:39 am »
I'm working on new front panel where I'd like to add few new features such as remote programming input and digital trigger input. For both of them I'd like to add some basic over-voltage protection and found two circuits that I believe can be used in both cases but they are differ in price and number of components. I'll present first as possible protection for analog input (remote programming) where allowed analog signal is in range from 0 ... 2.5 V:



Protection is accomplished using ADG465 Single Channel Protector with one TVS with higher breakdown voltage before it. Analog supply is +/-5 V.

Another circuit is copied from (heated) discussion that I found here. I added SN74LV1T34 buffer/shifter that allows various type of input logic voltage (1.8 to 5 V) as digital trigger signal. MCU is 3.3V therefore shifter is also connected to same voltage.



Please let me know what do you thing about above mentioned suggestions.
 

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Thinking about the next revision...
« Reply #228 on: February 08, 2016, 09:55:00 am »
I spent some time to summarize observations and obstacles found in the latest revision of the hardware part and see to which extent is possible to include it into the next revision. The following things asks for some attention and improvement:
  • The power supply (or just PSU) has two channels and their PCBs are mounted on two level using eight 50 mm spacers. Such construction does not allow access to the lower section (channel #2) when everything is assembled and e.g. we are willing to conduct some measurements on that channel.
  • Each channel is connected with digital control module (Arduino shield) using 10-wire flat cable (SPI-bus) and 2 x 2-wire cables (power output and remote sense input).
  • Each channel (indeed) require dedicated heatsink (two separate or one shared by both channel)
  • Both Arduino Mega2560 and Due boards are supported, but Mega’s price/performance looks pathetic in comparison to the Due. Support for Mega costs us 6 level shifters.
  • Two different type of digital isolators is used: 2- (input) and 6-channel (output). Such “careless” selection require additional two ‘125 logic buffers (one extra IC)
  • Using 4 mm binding posts for remote sense inputs looks attractive and robust but that’s “too bold” and many professional models use much smaller connectors. Additional obstacle is their location in between power output. Therefore no standard 750 mil (19.05 mm) distance between positive and negative posts was provided (that is recommended when e.g. BNC to 4 mm adapter has to be used).
  • Software triggering will be added into one of the following firmware releases, but it could be also interesting that some functions are triggered with external signal.
  • Similar to the previous one: there is no possibility to perform tracking functionality based on external signal. That is called “remote programming” and it could be helpful to use the PSU as a “smart” pre-regulator during development and testing with all additional features such as current limitation, OVP, OCP and OPP managed by the MCU.
  • The enclosure is fully packed: six PCB’s (+ piggybacked Arduino board), big main transformer and two heatsink are mounted outside the box. But still, is it possible to make it smaller with smarter organization and still without using mains voltage “pre-regulation” that can remove huge transformer from the scene?
The quest for the better solution was initiated with rearranging of the PCBs. Once again it’s started with selecting of suitable enclosure that has enough room for not less then two channels. This time an enclosure from the different line of the same manufacturer comes to mind (Galaxy Maggiorato) that comes with 1, 2, 3 or 4U (40 to 165 mm) height. The current enclosure is 115 mm high therefore 3U (120 mm) looks as good replacement. But such dimension is mainly dictated with the size of the Arduino shield PCB (200 x 105 mm) and that is result of vertical placement of the TFT display. Existing PCB is pretty crowded, but with smaller remote sense inputs, removing of 6 level shifters (Mega is out of game, but will be still supported by the firmware for a while), no ‘125 logic IC (better digital isolator’s selection) and minimizing output protection to only TVS (MOV and SAR are going out) we can rotate TFT and lower the PCB’s height below 80 mm. In that way even 2U (80 mm) enclosure starts to be a real candidate for the next revision!
Such reduction in volume (about one third) require new location of channel’s power modules (pre- and post-regulator PCBs). They could be eventually merged into single board but more importantly is to change their form factor that is suitable for mounting them not any more near the rear panel but on the side supports (one channel per each side). Above mentioned enclosure comes with 10 mm aluminium profile that possibly could safely dissipate up to 15 W (per side).
Moving channel’s PCB to the new position remove additional cabling from the picture (10-wire digital, 2 x 2-wire analog). Now we can plug power modules directly to headers located on the opposite ends of the redesigned Arduino Shield (of course here we must take care about rotation of pins because PCB’s are turned “face to face” and we don’t want to end up with “left” and “right” channel PCB variants!). 20-pin connector should be enough to carry all required signal and power lines.
It’s obvious that next revision is not a trivial one. In that case adding more stuff like what is mentioned in the last two bullets (digital trigger and remote programming) makes sense. An open question is where to locate input terminals for them: on the rear panel (that is quite usual for many professional models) or at the front panel? I think that for the bench power supply that is not mounted and forgotten somewhere in huge laboratory rack, front panel sounds more handy.
I tried to draw a new proposal using the FreeCAD, this is my first encounter with it so not many details are on the drawing that follows:





You can see that AUX power supply is now moved on the rear panel. There is also enough place to add 60 x 60 mm fan. The AUX power supply PCB with minor changes could be now used for mounting (vertical) USB and Ethernet connectors. One important thing that should not be skipped are limited ability of enclosure to dissipate a heat. That calls for more efficient solution and with currently used pre-regulator that is not a case. That topic will be discussed in one of the coming posts.
 

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Re: DIY programmable dual channel bench PSU 0-50V/3A
« Reply #229 on: February 08, 2016, 10:31:41 am »
A new PCB is created in accordance with issues mentioned in the previous post. I'd like to highlight few more details:
  • LED indications for Stand-by, CV, CC and remote sense are still there because I found that very useful and informative. But THT LEDs are now replaced with SMD and small lightpipes will be used (e.g. Bivar PLP2-500). Additionally two more LEDs are added as indication that remote programming is in use.
  • Fan control output (PWM) and fan sense input are added
  • Battery NTC is now available only on the channel one but it's isolated on-board (OK1) instead of doing that over post-regulator I/O expander input (that comes isolated to the shield).
  • Digital (external) trigger is available only on ch#1
  • "power switch" is added that will be become accessible from the front panel for people who don't believe that firmware could do that safely. It will disconnect +5V shield supply but still has no effect if USB cable is connected to the PC (to avoid that USB supply on the Arduino board should be modified by removing few components).
  • Ethernet RJ-45 jack is moved to the new AUX power supply board
  • Touch screen controller can be now programmed using software SPI (like UTouch library does) but also with hardware SPI (set JP3, JP4 and JP5).




 

Online prasimix

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New Arduino shield schematic...
« Reply #230 on: February 08, 2016, 10:34:57 am »
... and here is schematic (pdf is also enclosed):









 

Offline timofonic

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Re: DIY programmable dual channel bench PSU 0-50V/3A
« Reply #231 on: February 10, 2016, 04:05:30 am »
Your little beast grow! But it's looking more and more interesting. Congratulations.

What's that hat in the toroidal transformer? To me, a total novice, it just looks funny. What's the purpose for?

Digital (external) trigger is available only on ch#1

Why? What's the limitation for that?
 

Online prasimix

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Re: DIY programmable dual channel bench PSU 0-50V/3A
« Reply #232 on: February 10, 2016, 11:20:09 am »
I put so many thing on smaller PCB and just thought that adding second trigger will be too much because it requires 10 components for protection. Maybe protection is too complex, anyway it was placed on the bottom layer even in case of the first channel. If you think that two instead of one external trigger can be useful (e.g. to control each channel independently) and makes sense I'll try to put it on the board.
Also if you have any comment regarding proposed input protection (that has to protect MCU not power modules) please let me know.
« Last Edit: February 10, 2016, 11:33:49 am by prasimix »
 

Offline electricar

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Re: DIY programmable dual channel bench PSU 0-50V/3A
« Reply #233 on: February 10, 2016, 02:17:18 pm »
Hello prasimix,

I’m following your project quite a while and am very impressed of how passionate you are about this project. I really learned a lot, thank you!

Currently I’m designing my own power supply but forgive me if I use some of your ideas in my design, but why reinvent the wheel…
Currently I’m working on the pre-regulator and I ask myself why did you replace the solution with the LTC3824 or LTC3864 through the two mosfets?

Thank you very much in advance!
 

Online prasimix

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Re: DIY programmable dual channel bench PSU 0-50V/3A
« Reply #234 on: February 10, 2016, 03:26:41 pm »
Hi electricar, feel free to use whatever you thing that make sense for you. Regarding pre-regulator, I'd like to try SMPS build around LTC3864 since as SMPS it's in general more efficient then phase-controlled circuit and put less stress on the mains transformer. LTC3864 is particularly attractive because it is driving external P-ch mosfet that allows 100% duty circle. In that case for smaller output power (that we can control by MCU) you can completely remove switching noise that is otherwise difficult to remove. Higher efficiency become more important with new revision where I'd like to use enclosure for cooling (assisted by MCU controlled fan). It's also possible that LT4320 or Liv's "discrete comparator" sync rectifier will be used to further decrease power dissipation (each watt is counting).
 

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LTC3864 evaluation board
« Reply #235 on: February 12, 2016, 12:23:05 pm »
Dear people from LTC sent me an evaluation board for the LTC3864 DC/DC Controller with 100% Duty Cycle Capability. My intention is to use it as pre-regulator in the new design. The complete regulator circuit is really tiny and it’s located on both upper and bottom layer. PCB has 4-layer.



The board could deliver 5 V, 2 A with broad input voltage from 5 to 55 VDC. I tested it first without changing anything with load of little above 2 A (3.3 and 8.2 Ohm connected in parallel). The output (yellow) and input (cyan) ripple and noise is shown below (Vin=20VDC):



Improvement is visible with additional LC filter at the output (8.2uH + only 22uF):



Next step was to modify a board a little to be able to deliver variable output depending of the post-regulator output. Taking into consideration the rating of the power inductor, mosfet  and diode my intention was to not go over about 24 V with load of not more then 1.5 A. To accomplish that I first replace original voltage divider’s resistors used in feedback loop to set new output voltage. I got 24.5 V with 4.7K + 140K combination, and had a chance to desolder and solder 0402 size components for the first time :). Tested, everything works as expected so that in next step a “tracker” circuit can be added. 
I'm using a circuit that is mentioned in post #225 build around Q2. Additionally Q3 is added to test 100% duty cycle. It simply disconnect tracker from the feedback voltage divider (R9, R15) that has to be set very high - few volts over the max. input voltage. For mentioned combination that gives 24 V at the output, input voltage should not be higher then 20 V to insure that the controller will enter the 100% duty cycle mode.
A breadboard is used for connecting additional tracker components:




« Last Edit: February 12, 2016, 12:25:38 pm by prasimix »
 

Online prasimix

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LTC3864 evaluation board, Part II
« Reply #236 on: February 12, 2016, 01:28:47 pm »
For testing how LTC3864 board is working with tracker I’m using my PSU where first channel is set to 20 V and second one is used to control board output. First, I made a screenshot when no power is applied:



On the following screenshot is shown output after the filter and switch node signal when control voltage is set to 10 V (load is 0.3 A):



And now when Q3 is disabled LTC3864 goes into 100% duty cycle mode. Switching frequency is zero and output ripple and noise are as clean as possible.



I also tested how external switching frequency sync is working. Here is an example when external frequency (blue trace) is set to 390 kHz (Vin=33 V, Vset=9 V):



Now, I have to make a PCB that should reproduce comparable results. Hopefully I'll succeed regardless two obvious restrictions: everything has to be done on a 2-layer PCB and with larger components. Both of them could make a whole thing more noisy and unpredictable, but could lower the total cost and offer more flexibility for experimenting with higher voltage and current. My intention is to deliver up to 40 V (+ few Volts) and min. 3 A.
« Last Edit: February 12, 2016, 01:30:33 pm by prasimix »
 

Online prasimix

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Re: DIY programmable dual channel bench PSU 0-50V/3A
« Reply #237 on: February 12, 2016, 01:48:24 pm »
And yes, I forgot to mention that since new pre-regulator PCB has to be designed it's possibly the right time to test "sync rectifier" circuit and spare few watts by replacing a regular bridge rectifier. Two solutions comes to mind: that which Liv is using in his PSU and LTC's LT4320.
 

Offline timofonic

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Re: DIY programmable dual channel bench PSU 0-50V/3A
« Reply #238 on: February 12, 2016, 02:40:48 pm »
Quote from: prasimix on February 10, 2016, 10:20:09 PM
I put so many thing on smaller PCB and just thought that adding second trigger will be too much because it requires 10 components for protection. Maybe protection is too complex, anyway it was placed on the bottom layer even in case of the first channel. If you think that two instead of one external trigger can be useful (e.g. to control each channel independently) and makes sense I'll try to put it on the board.
Also if you have any comment regarding proposed input protection (that has to protect MCU not power modules) please let me know.


You are like 100x Widlar compared to me, my friend. Aren't there ICs with that feature?'

What kind of protections and what variables do you want? Maybe I can ask a friend or someone on the forum can have an idea.

Quote from: prasimix on Today at 12:28:47 AM
For testing how LTC3864 board is working with tracker I’m using my PSU where first channel is set to 20 V and second one is used to control board output. First, I made a screenshot when no power is applied:
......


Am I seeing a very good and noiseless output or it's just my ignorance? It's seems planer than my EKG these days :P

Quote from: prasimix on Today at 12:48:24 AM
And yes, I forgot to mention that since new pre-regulator PCB has to be designed it's possibly the right time to test "sync rectifier" circuit and spare few watts by replacing a regular bridge rectifier. Two solutions comes to mind: that which Liv is using in his PSU and LTC's
LT4320.


Damn. You are filling that project to become really LINEAR hehe.

How much are they? Do you know about the approximate BoM cost right now?
 

Online prasimix

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Re: DIY programmable dual channel bench PSU 0-50V/3A
« Reply #239 on: February 12, 2016, 04:28:43 pm »
Quote from: prasimix on February 10, 2016, 10:20:09 PM
I put so many thing on smaller PCB and just thought that adding second trigger will be too much because it requires 10 components for protection. Maybe protection is too complex, anyway it was placed on the bottom layer even in case of the first channel. If you think that two instead of one external trigger can be useful (e.g. to control each channel independently) and makes sense I'll try to put it on the board.
Also if you have any comment regarding proposed input protection (that has to protect MCU not power modules) please let me know.


You are like 100x Widlar compared to me, my friend. Aren't there ICs with that feature?'

What kind of protections and what variables do you want? Maybe I can ask a friend or someone on the forum can have an idea.

The external trigger is connected to the MCU, and I don't like an idea to do that directly. There are two reasons for that: MCU is 3.3 V and for digital triggers 5 V I presume is still the standard, therefore some level shifting is required. Another reason is overvoltage protection for what I suggested circuit presented in post #229. It looks fine for me. Maybe it could be simpler or more "secure". Idea is to survive typical ESD spikes that could be somehow comes from the environment. How many Volts and Joules I don't know.

Quote from: prasimix on Today at 12:48:24 AM
And yes, I forgot to mention that since new pre-regulator PCB has to be designed it's possibly the right time to test "sync rectifier" circuit and spare few watts by replacing a regular bridge rectifier. Two solutions comes to mind: that which Liv is using in his PSU and LTC's
LT4320.


Damn. You are filling that project to become really LINEAR hehe.

How much are they? Do you know about the approximate BoM cost right now?

Yeah, it's really depends, for quantity of one is around 5 GBP, but for 100 pcs it's twice cheaper. The same situation is with many other components used in this project. Because of that group buy or even crowd funding campaign structured to address different tastes from bare PCBs up to the completed unit could make a whole thing more realistic.
 

Offline electricar

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Re: DIY programmable dual channel bench PSU 0-50V/3A
« Reply #240 on: February 14, 2016, 11:48:24 am »
Hi prasimix,

thank you. I'm also trying to implement the LTC3864 but didn't get it quite stable in LTpowerCAD. I want an output of 30V 5A on my PSU. So the LTC3864 output voltage has to be a little bit higher. I'll have to experiment a bit to get it stable from 31V to ca. 5V with a 5A load.
The bridge rectifier solution is very nice! I didn't know that kind of approach yet :)
 

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Further Arduino shield modification (GPIO pin usage optimisation and W5500)
« Reply #241 on: March 01, 2016, 05:14:35 pm »
I'm playing with couple of additional details for Arduino shield that represents digital control of the PSU. The first one is to further reduce number of used MCU's GPIO pins. First thing that comes into mind is four lines used for CC and CV LED indicators (a pair per channel). For that we can use TLC5925's outputs by reducing power output LED indicators from two to one that should still be good indication about channel output state.

Another more challenging detail is replacing Microchip's ENC28J60 with Wiznet W5500. Such change would improve the solution with the following features:

1. Full and half duplex mode, auto negotiation
2. 10 and 100Mps connection speed
3. 32KB buffer memory
4. Reduced memory and MCU processing power usage

The price difference between them is almost non-existent (see ENC28J60 and W5500).
I got yesterday W5500 module from eBay and connect it to the Arduino Due:



It works "out of the box" where both power (+5V) and signals (+3.3V levels) are directly supplied from the Due. As chip select Digital pin 10 is used (SS) and thanks to Soohwan Kim (embeddist) library that is available on the GitHub I successfully tested few scenarios such as DHCP connection, Web server and NTP client.
 

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AUX PS with fan controller, Ethernet and USB connection
« Reply #242 on: March 04, 2016, 08:49:33 am »
New Auxiliary power supply board (r5B6) required for the revised Arduino shield board is finalized. It includes few minor changes as follows:

1. 4-pin "power" connector is replaced with 6-pin IDC connector for power (+5V) and signal lines (PWR_DIRECT, PWR_SSTART, FAN_CONTROL, FAN_SENSE)
2. Ethernet and USB connectors mounted on the reverse side that allows direct mounting on the new enclosure's rear panel (require 14 mm spacers).
3. Fan supply (+12V), PWM control and fan sense is added
4. Optionally Ethernet and USB could be guarded with surge protection circuits (IC3, IC4).
5. THT bridge rectifier (B1) is replaced with a SMD
6. Heatsink (KK1) is now SK 145/37,5





« Last Edit: March 04, 2016, 10:45:53 am by prasimix »
 

Online prasimix

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New power board (pre- and post-regulator merged into one)
« Reply #243 on: March 04, 2016, 10:22:45 am »
New power board (r5B6) schematic and layout are also finished. Pre-regulator and post-regulator sections are now merged and phase-control pre-regulator is replaced with the SMPS based on LTC3864 that also allows 100% duty cycle operation. The post-regulator section remains unchanged based on Liv's design that works happily on the two previous revisions for few months in the row.
The power board is directly connected to the Arduino shield using 26-pin 0.1" socket. Thanks to that 3 cables (SPI, power output and sense input) are removed from the picture. Only AC input (X1 connector) from the main transformer and optional Sync cable (X2, X3) now remains.
This revision includes also the following modifications and new features:
  • THT bridge rectifier is replaced with 4 SMD Schottky diodes (D1-D4). They will be additionally cooled via 5mm aluminium thermal bridge inserted between bottom PCB layer and the new enclosure side panel.
  • Down-programmer THT PMOS (Q8) is replaced with SMD version
  • THT or SMD power resistors could be used for down-programmer (R28) and quick current limit (R27)
  • Voltage programming could be local or remote selected using analog switch TS5A9411 (IC15). Remote programming input is protected with ADG465 (IC14).
  • On-board connectors for manual OE and DP switches and LED indicators were removed
  • On-board CC and CV LED indicators drivers and connectors were removed
  • Pass-element (Q4) is mounted below PCB directly on the new enclosure side panel that should be sufficient to dissipate ~15 W (3.5 W for D1-D4 and rest on the Q4 for voltage difference of up to 3.8 V). A hole on the PCB allows access to the Q4's mounting screw.













 

Online prasimix

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Power board ground layout
« Reply #244 on: March 04, 2016, 10:34:50 am »
A few words about ground layout. Main ground plane is located on the bottom layer. But before simply filling it I tried to make route to each ground connection separately that is visible on the picture below colored in magenta. All manually connected ground are additionally connected on top layer with trace colored light green. Also I added intentionally a separator (yellow) to split aux SMPS ground from rest of the signal ground. That signal ground meet SMPS power ground (light blue), SMPS analog ground (brown) and down-programmer ground (red) in single point (circled orange).

Your comments are welcomed :-/O.



 

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Arduino shield with W5500 Ethernet controller
« Reply #245 on: March 05, 2016, 10:55:47 am »
Here is the latest revision (r2B6) of the Arduino shield (digital control) board. It includes the following modifications:
  • Existing ENC28J60 Ethernet controller is replaced with W5500
  • One instead of two LED indicators is using for indicating power output status
  • Existing TLC5925 LED driver is now using for driving CC and CV LED indicators on both channels
New schematic and PCB are shown below (only Sheet 1 and 3 were changed). Also please find attached new pin mappings.
With this modification this revision is completed. I'm going to order a new PCB panel in coming days and if any other soul is courageous enough to follow me in this stage and want to order PCB panel please let me know, that will help me decrease the cost of this round.









 

Offline sangvikh

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Re: DIY SCPI programmable dual channel bench PSU 0-50V/3A
« Reply #246 on: March 05, 2016, 07:04:48 pm »
Looks awesome! I would be up for a group buy.

Is this thing strictly controlled via computer? I see no buttons or encoders on the front panel?
 

Online prasimix

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Re: DIY SCPI programmable dual channel bench PSU 0-50V/3A
« Reply #247 on: March 05, 2016, 10:46:00 pm »
No, it comes with 3.2" TFT color display and touch screen as a mean of local control and it can be controlled remotely using USB or Ethernet. Current firmware (M1) offer only remote control, and we are working now to add local control and first results will be presented soon.
 

Offline electricar

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Re: DIY SCPI programmable dual channel bench PSU 0-50V/3A
« Reply #248 on: March 10, 2016, 11:02:25 am »
Today I made some transient tests with our lab supply Agilent E3634A on the 25V/7A rail.
The voltage was set to 25V and the output current drawn was 1,5A. The load step was then 1,5A --> 3A.
Unfortunately I couldn't make any screenshots but the undershoot was about 250mV! So your 78mV are really amazing!  :D
The overshoot was a bit lower.
Kudos!
 

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Front and rear panel for the new enclosure
« Reply #249 on: March 13, 2016, 05:48:34 pm »
I spent some time to define all required holes together with silkscreen design for the new enclosure. The front panel illustration shows all LEDs active (colored) to have a better idea how it should looks like (of course there is no real scenario in which all of them are active in the same time).







The enclosure is Galaxy Maggiorato GX283 230 x 230 mm Black (but also can be Galaxy Maggiorato GX288 230 x 280 mm Black). Holes on the rear panel are intended for IEC connector with switch and fuse Bulgin BVA01/Z0000/10, Ethernet ( AMPHENOL LMJ2138812S0LOT6C) and USB (LUMBERG 2411-01) connector.
The power switch on the front panel is optional.

If someone is want to play with this a dxf and svg files are attached.
 


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