Half bridge buck circuit - record

        The recent use IR2104+NMOS The tube makes a half bridge BUCK Step down circuit , Do some process here 、 Record of experience .

        The circuit schematic diagram is shown below ：

         ● The driver chip used is IR2104, Recommended EG2104, Because I only have IR2104, So I make do with it , As long as there is no fake chip , There won't be a big problem .

        ● NMOS Tube based on input VCC The voltage of , Select the appropriate withstand voltage value , Under this premise, the smaller the internal resistance, the better （ It's like bullshit ）

        ● Bootstrap diode FR107 stay VCC No more than 40V You can use SS series （ Such as SS14） Schottky diode replacement , Include 1N4148、1N5819, In this way, only one diode model is more convenient for welding

        ● Switching frequency will affect MOS Loss of tube , That is, increase the calorific value , It is more obvious in the case of high current

       ● This record focuses on typical switching spikes and oscillations . Because for the circuit made for the first time , I usually have a sparse layout , Convenient for later debugging and testing （ The first time is more about finding problems and circuit characteristics ）, I didn't know before MOS There will be such problems , What problem is directly shown in the figure above is simple and clear

          The difference is NMOS On tube 、 The conduction waveform of the lower tube , The test conditions are VCC=30V, Output 12V、1.5A

          It can be seen that there are spikes and serious oscillations when the upper tube is switched , After consulting the information, I learned that this is a typical problem , I referred to this article later ：BUCK How on earth does peak oscillation occur ？      This is a very in-depth article , If you want to know more about it, you can take a look

        From this article , I can find that one of the problems of my board is the signal line of the upper and lower tubes , Drive the chip to NMOS The grid line is a little long , Later, the second time Layout when , I draw the layout more compact , Sure enough , Problem solved

         The following figure shows the conduction waveform of the upper and lower tubes , You can see , Almost perfect . The test conditions are VCC=30V, Output 12V、1.5A

   

          That's it , I hope it can help you .