This is to continue the last topic of the AC power adapter get hot in use and introduce how to improve it from the aspects of design, components selection and manufacturing process. In the process of practical application, the high temperature rise often occurs in two aspects: the MOS tube of the power transformer and the design of the transformer itself. Today we start from these two aspects. Let’s see how to effectively solve the problem of switching power transformer temperature rise too high.
Let’s begin with the transformer of AC power adapter, if the temperature rise is too high, it is mainly caused by four kinds of problems: copper loss, winding process problem, transformer iron loss and transformer design power is too small. No-load heating is that the transformer insulation is bad or transformer input voltage is high, insulation failure needs to rewind the coil, high input voltage need to reduce the input voltage or increase the number of coil. If the voltage is normal and is hot with load, it is that the load of the power transformer is too large and the load design needs to be changed.
In the design of transformer, the heating condition of MOS transistor is the most serious, and the problem of high temperature rise is caused by loss. The loss of MOS transistor consists of switching process loss and on-state loss. The on-state loss can be reduced by selecting the switch tube with low on-state resistance. The switching process loss is caused by the gate charge size and the switching time, and the switching speed can be chosen to reduce the on-state loss. The recovery time of the device is shorter to reduce. But more important is to design better control mode and buffer technology to reduce the loss, such as using soft-switching technology, can greatly reduce this loss.
In addition, there is a possibility that the temperature of the power transformer itself is too high, that is, the transformer itself has an aging phenomenon. When the engineer checks the transformer itself and the MOS tube has no abnormality, it is necessary to combine the working time and working life of the transformer to make a comprehensive judgment.