GOPHERT CPS-3205 II power supply

Table of Contents

1 Hardware

The GOPHERT CPS-3205 II power supply is a very cheap lab power supply that can be purchased for example on aliexpress. It has two boards inside:

  • a main power board
  • a smaller controller board screwed in front

Both boards are connected using a short bundle of wires with pins labeled on both ends. The wire is marked as SW19 on the controller board.

thumb-controller-board.jpg

Main chips on the controller board are:

Designation Label Notes
U1, U2 74HC595D 8-bit shift registers
U3 STM8S105K4T6C  
U4 LM358A Dual opamp
U5 LD1117AG-33  

Connectors visible on the back of the controller board:

thumb-controller-board-connectors.jpg

1.0.1 SW19 connector

Pin Label Purpose Notes
1 C.S Current sense See below for input voltage ranges
2 V.S Voltage sense See below for input voltage ranges
3 C.C Constant current set See below for output voltage ranges
4 GND    
5 +5V Power for controller board  
6 C.V Voltage set 05.00 V set -> 0.534V, 15.6 V set -> 1.563 V, 32.3 V set -> 3.17, 0.1 of output voltage
7 0/1 Output switch HIGH -> Output OFF, LOW -> Output ON

The current settings on the power supply maps to the voltage on the C.C pin in the following way:

Setting [A] C.C voltage [V]
0 (MIN) 0.022
0.5 0.640
1 0.914
1.5 1.188
2 1.462
2.5 1.737
3 2.00
3.5 2.27
4 2.55
4.5 2.82
5 3.10
5.1 (MAX) 3.15

After running a simple linear regression using http://www.xuru.org/rt/LR.asp#CopyPaste on this data we find out that the relationship between the display and driving voltage is:

C.C voltage [V] = 0.573 * Current [A] + 0.264

Corresponding table mapping the voltage seen on the C.S pin and the current displayed is provided below:

C.S voltage [V] Current display [A]
1.055 0.004
1.131 0.049
1.218 0.102
1.385 0.202
1.579 0.318
1.747 0.418
1.908 0.513
2.11 0.636
2.23 0.705
2.42 0.816
2.58 0.912
2.78 1.031
3.06 1.195
3.38 1.384
3.78 1.619
4.09 1.803
4.43 2.008
4.66 2.145
4.81 2.235
4.88 2.275

I measured only up to 4.88 as I was the top I could reach with a simple potentiometer connected to a 5V rail. But this should be enough to calculate a linear regression:

Current display [A] = 0.593 * C.S voltage [V] - 0.619

The same for mappinv between the voltage on the V.S pin and the voltage diplayed:

V.S voltage [V] Voltage display [V]
0.156 0.21
0.192 0.27
0.301 0.46
0.417 0.66
0.516 0.84
0.607 1.00
0.726 1.21
0.859 1.44
0.919 1.54
1.055 1.78
1.138 1.92
1.208 2.05
1.273 2.17
1.332 2.27
1.397 2.39
1.476 2.52
1.574 2.69
1.658 2.85
1.738 2.99
1.816 3.11
1.896 3.25
2.03 3.49
2.10 3.61
2.17 3.72
2.21 3.8
2.30 3.96
2.39 4.13
2.51 4.33
2.62 4.53
2.70 4.67
2.80 4.85
2.90 5.03
3.00 5.20
3.11 5.40
3.20 5.55
3.30 5.72
3.41 5.91
3.51 6.10
3.58 6.22
3.70 6.43
3.80 6.60
3.99 6.94
4.11 7.16
4.20 7.31
4.31 7.50
4.43 7.72
4.50 7.84
4.64 8.08
4.71 8.20
4.80 8.37
4.90 8.54
4.91 8.56

Voltage display [V] = 1.757238498 * V.S Voltage [V] - 0.0723

1.0.2 CON2 connector

The second unpopulated connector on the board is used for programming of the microcontroller.

Pin Label Notes
1 RESET  
2 GND  
3 SWIM  
4 +3.3V Power output from internal voltage regulator. Board needs to be powered using +5V input.

I tried to read the firmware with an STLINKv2 interface but unfortunately the readout is locked.

Created: 2020-06-24 17:57

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