Some repair shops, limited by conditions, do not have a three-phase maintenance power supply, which brings inconvenience to the repair of inverters, especially AC/DC voltage regulators (soft starters) and other electrical equipment. After several experiments and optimizing the structure, I made a three-phase inverter power supply. When testing the output waveform, wow! It is very close to the industrial frequency power supply. When assembling inverters that use a 380V three-phase power supply, it is necessary to add a KT1 delay charging circuit, whose parameters can be the same as those of the internal charging circuit. The isolation transformer uses a 1:1 turns ratio; if using an inverter with a 220V input power supply, the KT1 current-limiting link can be omitted, and the isolation transformer uses a 220:380 step-up transformer. Choose R2=R1, and the contact capacity of KT1 should be greater than 5A; if insufficient, add a relay. According to needs, T1T2 can be configured based on the inverter's output current. I configured it using readily available second-hand inverters, second-hand isolation transformers, and second-hand reactors that were idle at hand. If needed, a rectifier and filter circuit can be added at the later stage to obtain an adjustable DC maintenance power supply of 0~550V. When the output waveform is not ideal, try adjusting the inverter's carrier frequency to adapt to the LC filter time constant, thereby achieving a better waveform output. There are many methods to obtain current signals at the debugging site, such as using a 24V or 10V power supply in series with a current-limiting resistor, but it is still inconvenient. If there is a portable adjustable current generator with current value indication, it would be much better.I purchased a 91C4 type 30mA pointer meter head and a WS-1 type 300Ω0.5W adjustable potentiometer online, found an ordinary 51Ω resistor, prepared a 9V power supply and battery socket, selected a soap box from the supermarket, and used ready-made multimeter test leads for the test wires. With all materials ready, I started making it. Due to low power consumption, contact us LM317 does not need a heat sink. The load resistance at the current signal input terminal is best at 250Ω or less. To ensure maximum current output capability, company news. It is recommended to increase the supply voltage, such as using a 12V or 24V power supply (two 9V batteries in series is also a good method).Usage: 1. First short-circuit the test leads, adjust the potentiometer knob, and observe the current meter indication. It should vary within 4-20mA. This is the detector test; 2. Connect the test leads to the current signal input terminal, adjust the knob, and send the current signal required by the debugging equipment. Step 1 can be omitted and directly proceed to step 2. Uses: 1. For testing the quality of the relevant signal input circuits of instruments or inverters and other electrical equipment; 2. For debugging during installation or maintenance of equipment.