Linear MOSFET Electronic DC Load — Part 1

Linear MOSFET DC Load module assembly.
Linear MOSFET DC Load mod­ule assem­bly.

A new project for 2017, the dual channel 300 W
programmable DC electronic  load.

I just fin­ished test­ing the pro­to­type DC Load Module for the project, and except for a few small issues with hole diam­e­ters all went well. The ini­tial test was at 25 volts and a load cur­rent of 3 amps, for a total dis­si­pa­tion of 75 watts.
The goal of the project is a pro­gram­ma­ble, dual chan­nel DC elec­tron­ic load capa­ble of 300 watts and a max­i­mum of 30 volts and 13 amps.
The micro­proces­sor I plan on using for the project is the Teensy 3.2, and the cur­rent plan is to mount every­thing in a reused HP 6200‑B pow­er sup­ply enclo­sure.

DC Load Module circuit board with current shunt resistor and OpAmp mounted.
DC Load Module cir­cuit board with cur­rent shunt resis­tor and Op-Amp mount­ed.

What makes this load mod­ule dif­fer­ent than many of the past MOSFET based elec­tron­ic loads, is the IXYS  IXTX110N20L2 Linear MOSFET. This MOSFET was designed to oper­ate in the lin­ear oper­a­tional region with an extend­ed FBSOA.
The MOSFET has a max­i­mum rat­ing of 200 volts and 110 amps. So a sin­gle MOSFET should meet and exceed my design require­ments.
I includ­ed a Maxim Integrated 44284AUT cur­rent sense ampli­fi­er with a gain of 50, on the load mod­ule close to the 4‑wire sense pins of an Ohmite 0.005 ohm cur­rent shunt resis­tor.

Initial testing of the DC Load Module at 25 volts and 3 amps
Initial test­ing of the DC Load Module at 25 volts and 3 amps

The heatsink is a Wakefield-Vette OMNI-UNI-41–75, which can be mount­ed as a pair with a 60 mm fan cool­ing the main fin chan­nel. The fan is rat­ed at 40 cfm at 1 ” H2O pres­sure. It will be inter­est­ing to see how well the fan / heatsink com­bo keeps the MOSFET at a safe tem­per­a­ture under a full load. I may need to add a sec­ond MOSFET just to spread the heat more even­ly across the heatsink.
I still need to make some volt­age drop mea­sure­ments of the cir­cuit board under full load to ver­i­fy that the pro­to­type cir­cuit board with 1 oz cop­per traces will han­dle a con­tin­u­ous load, or if I will need to change to 2 oz cop­per traces.
I have already com­plet­ed some ini­tial test­ing of the cur­rent sense Op-amp with the Teensy 3.2 micro­proces­sor, but still need to fin­ish the MOSFET con­trol design.

Dual channel DC electronic load assembly with 60 mm fan attached.
Dual chan­nel DC elec­tron­ic load assem­bly with 60 mm fan attached.

More to come…

6 Replies to “Linear MOSFET Electronic DC Load — Part 1”

  1. I am very inter­est­ed in see­ing how you are pro­gress­ing with this project. I just ordered a pair of heatsinks, a hand­ful of the MOSFETS, and the 4 wire cur­rent sense resis­tors in prepa­ra­tion for mak­ing my own 🙂

  2. Have you shared the lat­est ver­sion of the PCB for this? I saw your March 2016 update and am look­ing to build this ver­sion, with or with­out the uC con­trol… I have a real need for a DC load and I love this design so far.

    Thanks!

    SH

    1. Hi Sonny,
      I am mak­ing slow but sure progress on the DC Load project. The L2-MOSFET boards are most­ly done with the excep­tion of some minor spac­ing issues with the 0.5 ohm bal­ance resis­tors.
      The MOSFET boards do need to be made using 2oz 0.8mm cop­per. I am also in the process of chang­ing the MAX44284F (50V/V) to the MAX44284H (100V/V) to match the cur­rent range on the con­trol board.
      Heat-sink com­po­nents must be mount­ed before installing the 4 ter­mi­nal cur­rent shunt resis­tor oth­er­wise it inter­feres with the clamps.
      Link to the Eagle CAD V7.7 Rev 0.2 ZIP file is below. Use at your own risk as there have been small changes since the last test­ed ver­sion.
      https://www.barbouri.com/assets/ThermalSingle02.zip

      Greg (Barbouri)

    1. Hi Krong,
      Currently no progress on the DC Load project, as I am using all my free time on test equip­ment repairs.
      Basically the MOSFET DC Load sec­tion is fin­ished only requir­ing a con­trol sec­tion.
      The con­trol sec­tion can be as sim­ple as an op-amp and poten­tiome­ter to set the cur­rent.

      Greg (Barbouri)

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