Simple CNC Adjustable Power Supply

I. Module Introduction:
A low-power, simple, digitally controlled adjustable power supply designed based on STM32 and DCDC chips.
 
II. Application Scenarios

: Experimental debugging power supply;
Other load debugging.

 
 
III. Module Overview :

Module DP2503-75-GPL.
This module uses STM32 as the main control chip
. This power supply module is a switching power supply, a non-linear power supply.
This module is a buck topology power supply, which can only step down, not step up. The maximum output voltage is always lower than the input voltage.
The input interface is a TYPE-C interface (supports PD2.0/3.0 fast charging protocol, maximum handshake voltage is 20V, supports 45W or 65W PD power adapters).
The output interface is an XT30 (male).
This module has constant voltage and constant current functions
. This chip has excellent load step response capability and low ripple.

 
IV. Module Parameters

: Minimum input voltage: 12V;
Maximum input voltage: 30V;
External MOSFET, synchronous rectification architecture;
Adjustable voltage range: 1-25V
; Adjustable current range: 0-3A;
Fixed switching frequency: 200KHz
; With 4 micro-switches (function selection, decrease, increase, confirm).
1.5-inch LCD screen (240*240 resolution)

 
V. Instructions for Use

Use a charger with PD2.0/3.0 fast charging protocol. Connect the USB data cable to the TYPE-C terminal on the left side of the module. The XT30 terminal on the right is the output terminal, which can be connected to electronic loads or other loads.
After powering on, use a multimeter to test whether the output voltage reaches the set value. If it does not reach the set value, do not connect a load.
The positive and negative terminals of the output cannot be reversed, as this may damage the module or other loads.

 
VI. Precautions and Remarks

Precautions: For long-term operation, it is recommended to use a current within 2A (pay attention to temperature rise).
The design of separating the power board and control board greatly improves heat dissipation and also increases space utilization.
The module does not have reverse current protection. It is not recommended to use this module to charge batteries, as this may damage the module.
Do not frequently short-circuit the output interface. Although the module has a constant current function to limit and protect, it may still damage the module.
Therefore, this is a step-down module. Please maintain a certain distance between the input and output. The voltage difference is important. It is recommended that the input voltage be at least 3V greater than the maximum output voltage.
Do not change the materials used in this module without authorization. Technical support will not be provided for any module malfunction or failure to operate properly due to unauthorized material changes.
This project is for DIY and learning purposes only and is prohibited from being used for any form of commercial use or other forms of commercial development.
To avoid subsequent problems, the program files for this project are not provided, only the hex firmware is provided.
Reproduction is prohibited without the author's authorization.

 
VII. Version Update

Software V1.0, first release. Current issues: slow response of function selection buttons; pressing the confirmation button when adjusting voltage or current may return to the voltage and current setting interface.

 
Welding power board
 
from another angle.
 
Welding control board (back).
 
Welding control board (front).
 
Originally, it was planned to use 10mm copper pillars for support, but it was found that the connector distance between the power board and the control board was insufficient, so only 8mm copper pillars could be used. If 8mm copper pillars are used, it will cause structural interference between the micro switch and the inductor. The inductor needs to be moved a certain distance to provide support for the micro switch. The button provides some space.
 
Screws are made of M3*5mm and 8mm double-through copper pillars.
 
The finished product is shown from
 
another angle .
 
Due to a design error in the schematic, SWDIO and SWCLK were reversed, causing the program to fail to download. Cross-wiring is required for SWDIO and SWCLK.
Note: This uses a special program download interface, which needs to be compatible with other modules. Changing the wiring sequence is difficult. If using a regular programmer, simply change the wiring sequence manually and ignore this issue.
 
During power board debugging, the chip was found to be malfunctioning, with no waveform at the SW node and MOSFET gate. Checking the schematic revealed that pins 17 and 19 were incorrectly connected, preventing the bootstrap capacitor from charging, thus preventing the chip from working properly.
 
Cross-wiring was performed at pins 17 and 19. Another issue is that the chip needs to operate in FPWM mode. This was not considered in the schematic design and requires manual wiring to change it. A 20K resistor is connected in series from pin 8 to the +10V power supply.
 
Software Still under testing. The UI is shown above and shouldn't have major changes. Originally, hardware SPI was planned for screen refresh, but problems arose with this screen; the screen frequently failed to display for unknown reasons (although the program was running normally). Later, software-simulated SPI was used, which allowed the screen to display correctly, but the speed was much slower than hardware SPI, significantly impacting the entire debugging process. The
 
output interface uses an XT30 male connector, but the positive and negative terminals were reversed during schematic design. This means that when soldering the female connector to the male, the positive and negative markings on the casing cannot be followed; they must be reversed.
 
 
The module output ripple is shown in the image above. Under 5V output, the no-load ripple is slightly higher than under load, exceeding 1%.
 
The switching node waveform is normal with no obvious ringing. The dynamic load step response is approximately 2.5%, which is average performance, not very good. The bandwidth appears low, and the parameters need further adjustment.
 
The low-load temperature is shown in the image above and is not too high. The high-temperature area is not in the power section. The LDO (Light Detector) section has the highest temperature, likely due to the high backlight current of the screen. The LDO's higher voltage
 
drop results in a higher temperature under high load, as shown in the graph above. The power section's temperature is significantly higher under lower load. The hottest area is the PD (Power Delivery) protocol chip, possibly due to its high input voltage, exceeding the maximum voltage specified in the datasheet.
 
With a relatively small input-output voltage difference, high efficiency can be achieved; with a 20V input and 18V output, efficiency can reach approximately 97%.