In common power supplies, the voltages that are often used are mostly positive voltages, and the positive voltages are easy to understand. Taking the earth as the reference ground, it is the 0V voltage, and the voltages higher than the 0V voltage are all positive voltages.
However, in notebook power supplies and communication power supplies, more and more negative voltages are used as reference voltages or bias voltages. The ATX power supply sold in the market has a total of five output voltages, including four positive voltage outputs and one negative voltage output. Negative pressure output -12V/0.5A, output power is 6W. So what if negative pressure output is achieved? It is usually necessary to convert the internal positive voltage to a negative voltage and then output it.