Below is the maximum ratings for 2N3904 NPN BJT. As you can see the maximal Emitter-Base voltage is 6 V. I have checked many other BJT datasheets which all show that this voltage is around this value. But in my circuit the Emitter-Base voltage of NPN BJT will be over 6 V which causes the operation is not normal. I konw by connecting a diode to the emitter of the BJT in series can improve the problem. Is there another better method? Thanks in advance!