New display boards for Power Designs D‑Series power supplies

Power Designs D series 4-digit ADC/LED Rev 2.0 board
Power Designs D series 4‑digit ADC/LED Rev 2.0 board

Designing and build­ing a replace­ment dis­play for the Power Designs, Inc. 6010D pow­er sup­ply, and oth­er Power Designs D‑series supplies.

After restor­ing my Power Designs 6010D and using it for a short while, I was miss­ing hav­ing the extra dig­it of res­o­lu­tion from the upgrad­ed PD 6050C dis­play.
Luckily one of my read­ers, Ron Metcalf adapt­ed my 6050C dis­play boards for use on his 6050D pow­er sup­ply. He start­ed with my orig­i­nal design, and updat­ed it by using a card edge con­nec­tion, remov­ing the pow­er sup­ply sec­tion and volt­age divider, and chang­ing the range to 200 mV.

OTE ADC/LED main board ready to install
OTE ADC/LED main board Rev 1.0 ready to install
Power Designs D series 4-digit display board
Power Designs D series OTE 4‑digit dis­play board Rev 1.0

It seems that most of the Power Designs D‑series pow­er sup­plies use this style of edge-con­nec­tor dis­play. The OEM dis­play uti­lizes a 200 mV input range to dis­play three dig­its on it’s red LED dis­play. For the 6050D and 6010D mod­els the max­i­mum dis­play input volt­age is around 60 mV for the max­i­mum volt­age out­put of the sup­ply. The OEM mod­ule uses a Intersil ICL7117 3½ dig­it inte­grat­ing ADC and LED dri­ver IC, which is also avail­able as a Maxim Integrated ICL7117 part.

OEM 3½ dig­it dis­play mod­ule with IC removed

The OEM dis­play is pow­ered by 5 volts sup­plied from a lin­ear reg­u­la­tor on the main board thru two pins. Two of the edge-con­nec­tor pins are used for the 200 mV dif­fer­en­tial input. The oth­er three con­nec­tions to the OEM dis­play mod­ule are a 560 Ω pull­down con­nec­tion to ground, and two dec­i­mal point select input con­nec­tions. The three dec­i­mal select and pull­down con­nec­tions all con­nect to the meter V / A front pan­el tog­gle switch.

Rev 1.0 bare boards
OTE Rev 1.0 bare boards front and back

I ordered a set of Ron’s boards from OSHpark to try on my Power Designs 6050D and 6010D sup­plies, and built up a pair of them.
Both sets of boards were easy to assem­ble, and worked well. The 7 seg­ment red LED dis­plays that Ron picked for the dis­play board were almost a per­fect match com­pared to the OEM mod­ule.
The only issue that I ran into was a mechan­i­cal prob­lem and not an elec­tri­cal one, in that the parts list spec­i­fied a 6–32 thread size, but the orig­i­nal screws and holes were a 4–40 thread size includ­ing the new boards.
I end­ed up using a part num­ber 4504–440-AL‑7 hex stand­off #4–40 by 7/16″ and the orig­i­nal screws and nuts from the OEM module.

PD 6010D with Rev 1.0 boards installed
PD 6010D with Rev 1.0 boards installed

With the extra dig­it of res­o­lu­tion I was get­ting some dig­it noise on the 10 mV dis­play posi­tion of around 30 mV. This was hap­pen­ing on both upgrad­ed sup­plies.
On the OEM dis­play mod­ule with only 100 mV res­o­lu­tion, this noise is not a notice­able issue. I was also not see­ing this behav­ior on my mod­i­fied 6050C dis­plays.
My the­o­ry of what maybe caus­ing the issue is the 200 mV meter range of D‑series units com­pared to the 2 volt meter range of the 6050C.

PD 6010D with Rev 1.0 boards installed, load testing
PD 6010D with Rev 1.0 boards installed, cal­i­bra­tion, sta­bil­i­ty, and load testing

Even though the Rev. 1.0 boards were work­ing, I decid­ed to design a Rev 2.0 board with a 2 volt input range. I also want­ed to make sev­er­al small changes to the input cir­cuit­ry, and com­po­nent spac­ing on the board while I was at it.
I want­ed to con­tin­ue using the orig­i­nal Rev 1.0 LED dis­play boards designed by Ron Metcalf, but want­ed the option of dis­abling one or both of the mode LED’s, so I added a set of jumper pads on the ADC board for the mode LED’s.

Power Designs D-series display ADC / LED Rev 2.0 loaded board
Power Designs D‑series dis­play ADC / LED Rev 2.0 loaded board

The lin­ear volt­age reg­u­la­tors were moved to the out­er edges of the cir­cuit board to reduce the heat trans­ferred to MAX1447 IC and its inter­nal volt­age ref­er­ence. I also increased sev­er­al of the fil­ter capac­i­tor val­ues to reduce noise on the pow­er rails. The ref­er­ence fil­ter capac­i­tor was increased to 10 uF for addi­tion­al ref­er­ence noise reduc­tion.
I added a pair of low noise series 100 Ω resis­tors to the dif­fer­en­tial inputs, along with a 10 uF dif­fer­en­tial fil­ter capac­i­tor, also increas­ing the com­mon mode fil­ter capac­i­tors to 1 uF.
Another change was switch­ing the DPON, INTREF, LED_EN, and DPV/DPA select source to the DVDD 3.3 volt pow­er rail. The foot print was changed for trim­mer resis­tor R1 due to lack of avail­abil­i­ty with the Rev 1.0 500K trim resistor.

PD 6010D with Rev 2.0 ADC/LED board installed

Well now I have a 2 volt input board installed in a 60 mV sig­nal 5010D pow­er sup­ply.
Time to change the volt­age dividers on the main board that I don’t have a schemat­ic for.

After a hour of cir­cuit trac­ing and ver­i­fy­ing resis­tor val­ues I was able to change resis­tor R56 in the 6010D volt­age cal­i­bra­tion cir­cuit with a 1.74K Ω 1% 50 ppm resis­tor, part num­ber CMF501K7400FHEB. This changed the ratio from 1000:1 to 100:1 and pre­sent­ed a 0.6 volt meter input with a sup­ply out­put of 60 volts. I also changed the volt­age cal­i­bra­tion cir­cuit trim poten­tiome­ter R54 to a 50 Ω 20 turn unit part num­ber 3299Y‑1–500LF, for ease of adjust­ment.
The cur­rent cal­i­bra­tion cir­cuit is made up of R52 a 649 Ω 0.05% 100 ppm resis­tor, with R12 a 5.1 Ω resis­tor and R53 a 10 Ω trim­mer poten­tiome­ter. After sev­er­al tries I end­ed up replac­ing R12 with a 120 Ω ±0.1% resis­tor part num­ber CMF55120R00BHEK. This gave me a 150 mV meter input for a out­put cur­rent of 1.5 amps.

Power Designs 6010D power supply with Rev 2.0 ADC/LED board installed
Power Designs 6010D pow­er sup­ply with Rev 2.0 ADC/LED board installed and mode LED’s off

After upgrad­ing to the Rev 2.0 board all of the dig­it flick­er­ing stopped, and the dis­play was very sta­ble with no dis­play drift after warm-up and full load test­ing.
Unfortunately I made many changes to the board, so I don’t know if a sin­gle or mul­ti­ple changes made the dif­fer­ence. My sus­pi­cion is that chang­ing to the 2 volt input range, made the biggest dif­fer­ence in sta­bil­i­ty but I have no way to cur­rent­ly prove it.
The upgrad­ed PD 6010D is being used for an upcom­ing audio ampli­fi­er project, for my old Nakamichi 420 pow­er ampli­fi­er. I am enjoy­ing that extra dig­it of res­o­lu­tion.

I am cur­rent­ly look­ing for a PD 5015D unit which this dis­play upgrade should also work with, along with man­u­als for these D‑series supplies.

EagleCad V7 board and schemat­ic ZIP for ADC / LED dri­ver Rev 2.0 board only
Link to OSHpark ADC / LED dri­ver Rev 2.0 shared board page
PDF Bill Of Materials for the ADC / LED dri­ver Rev 2.0 board

Link to Ron Metcalf’s meter project PDF page
Link to Ron Metcalf’s OSHpark Rev 1.0 4‑digit dis­play board page

I have had sev­er­al requests for a 200 mV full scale (FS) input board, which should­n’t require any changes to the sup­plies main board. So here it is.

EagleCad V7 board and schemat­ic ZIP for ADC / LED dri­ver Rev 2.1 board 200 mV FS
I haven’t test­ed this board, but there are only a few small changes from Rev 2.0
If you build it, please let me know if it worked well for you, Thanks!

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