Every home laboratory needs a power supply with adjustable voltage and current for the implementation and testing of prototypes and custom projects, or for repairs. Of course, such devices are commonly available for purchase in electronic component and measuring instrument stores.
The presented design of the laboratory source differs somewhat from the common concepts of such devices. Most amateur projects focus on implementing the classic approach, i.e. transformer, rectifier, filter, regulator, measuring output values, regardless of whether they are classic analog circuits or switched-mode power supplies.
A seemingly trivial task can be a challenge even for an experienced designer. The designer must solve problems with heat dissipation, accuracy of measurement values, in the case of analog power supplies the limiting factor is the size and weight of the transformer, as well as the maximum required output values. Switched power supplies significantly reduce dimensional and power limitations, but problems with the range of regulation, interference to the powered circuits, or to the network increase. The designed laboratory power supply circumvents these problems by using professional ready-made power supply blocks, at an affordable price.
Commonly available laboratory power supplies have an output voltage of up to 30V and an output current of several amperes, i.e. a power of several hundred watts. I own such a power supply myself, but sometimes the need for a larger range of output voltage and especially current (for example, in experiments with anodizing or induction heating) led me to implement this power supply.
entry requirements:
two independent isolated outputs
output voltage range 0 - 50V
output current range 0 -20A
highest output power
low interference level on both sides
best measurement accuracy
easy to use
reasonable price
Based on the chosen concept, I selected the following key components::
power source MS-1500-72 , RIDEN RD-1500-68 , or other similar suitable typeXY6020L DIY laboratory power supply 20A 1200W
The overall wiring diagram is shown in the following figure.:
The basis of this laboratory power supply is the XY-6020L module, which is a "step down" switching power supply. The basic characteristics include output voltage and current accuracy below 1%, output ripple up to 100mV and power 1200W. Overvoltage, overcurrent and overheating protection are not even mentioned. The XY6020L power supply module can be controlled using a control module with an LCD display connected through connectors, or via a serial bus Modbus. I chose control via modbus. From the above diagram of the wiring diagram, it is clear that the 230V supply is via connector X1. Behind it is fuse F1, protecting the entire device from current overload in the event of a power supply failure. PWR1 and PWR2 provide AC/DC conversion from alternating 230V to 64V direct current (the output voltage is set by a trimmer in the power supply). The set output voltage of these sources must be less than 65V, otherwise the PWR4, PWR5 modules (XY6020L) will go into a blocked state, due to overvoltage at their input. The PWR4, PWR5 modules are step-down converters providing the required voltage and current values at the output terminals X4-X7. The required voltage and current values are entered via the ER-DIS08050H touch HMI display. The time relay XT1 is used for delayed connection of PWR1 to the 230V network after switching on the main switch SW1, in order to prevent overcurrent from the transient phenomenon of charging the power supply capacitors when switching on. PWR3 is a +5V source for powering the display and auxiliary control circuits. PWR6 is a ZVS1000 induction heating module, which I built into the cabinet of the described laboratory power supply. The switch SW2 connects the power supply from the PWR5 source to the input of the induction module. The output of the high-frequency module PWR6 is output to terminals X8 and X9, as well as to the pins of the connector X3, which must withstand a current load of at least 20A. The switch SW3 is used to activate the output of the second source, which powers the induction module, as long as it is pressed. An important part of the laboratory power supply is the Modbus adapter circuit, which provides galvanic separation of the serial lines through which the XY6020 power supply module is controlled and mediates communication with the HMI display for entering and displaying desired values.
The modbus adapter circuit is powered by a 5V PWR5 power supply. The serial lines of the modbus interface of the XY6020 power supply modules (PWR4 and PWR5) are connected to the X2 and X3 connectors of the modbus adapter. The ¶122M30 integrated circuits ensure galvanic separation of the serial lines, so that the output voltages of the power supplies have independent potential and can be combined in series, which will allow achieving a stabilized output voltage of up to 120V at a maximum output current of 20A.
The U1 microcomputer provides communication via the Modbus protocol with the XY6020 sources and via WiFi via the TCP protocol with the HMI display, which is also equipped with an ESP32 microprocessor. The capacitors used have a filtering function and the resistor R1 has a value of 0 Ohm and I used it only to simplify the PCB, so that it could be implemented as a single-sided PCB. The PCB has dimensions of 100mm x 50mm. The printed circuit board motif and component placement are shown in the following figure:
Since the majority of the hardware is assembled from ready-made modules, the greatest effort had to be devoted to the software. The operating programs are written in Micropython, which is a python programming language optimized for use on embedded systems with limited resources. Communication between the display and the Modbus interface board takes place via WiFi using the TCP protocol. The display board is in client mode and the Modbus interface board is in AP mode. All necessary programs can be downloaded in the DOWNLOAD section. On the AP side, the main program is main_AP.py. The following line needs to be added to boot.py:
The control screen looks like this:
The screen displays four digital displays to display the current voltage and current of each source. Placing a finger on the capacitive screen in the place of the displayed voltage or current value will display a numeric keyboard on the screen for entering the desired value. Entering input values is completed by pressing the "enter" key on the keyboard, or by entering four characters, whichever comes first. Values are entered from left to right; if less than 4 characters are entered, zeros are placed at the bottom. For example, 0+5+"enter" means 05.00 volts, or amperes. The number of decimal places is fixed at 2. When displaying the output values of the source, the leading zero is suppressed. The desired value is displayed below the voltage and current data (in blue in this illustrative image). Below this are the start and stop buttons for each source, and in the middle is a button for calling up the information screen, where data on the firmware, input voltage of the XY6020 sources, source temperature, and others are displayed.
The top row is reserved for status indications. In the left part after the status name, OK is displayed if everything is fine, or a red x if an error occurs. Icons in the left part of the status bar indicate the ongoing activity, or the source of the error. 
The icons from left to right indicate, by changing color and acoustic signal, an error on the Modbus resource bus, an error on the TCP connection between the client and the server, a wifi connection error. The triangle icon with an exclamation mark indicates in orange the overheating of the XY6020 module and the last icon indicates by blinking the loading of large fonts during booting.