I. Preface
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In the near future, we need to design a power half-bridge circuit, and we are ready to use the IR2181s chip we just purchased to drive the MOS tube half-bridge, and build a simple circuit for testing to lay the foundation for the subsequent application circuit design.
2. Circuit design
Design and test boards, including the microcontroller G030, using the IR2181 to drive two power MOS transistors. The following uses the 1117 to provide a 3.3V working power supply for the microcontroller. Lay the single-sided circuit board and get the test board after one minute. The board is perfectly made. Next, the welding test.
▲ Figure 1.2.1 Experimental schematic
▲ Figure 1.2.2 Experimental PCB
3. Welding test
The circuit board is soldered, cleaned and used for the following tests. In order to test the functionality of the IR2181, the two power MOS tubes were not welded first.
The DAP LINK is plugged into the circuit via a spring clip. Use CubeMX to generate a program framework to write an LED flicker test program. Once downloaded, you can see the circuit start running. This shows that the circuit design and soldering are basically normal. Let's test the output PWM signal.
Through the software, enable the TIME1 complementary PWM output. Using an oscilloscope to measure the TIME1 PWM two output signals, you can see the output PWM signals, which are reversed from each other.
▲ Figure 1.3.1 PWM signal with two outputs
Solder two N-channel MOS power tubes to the circuit board. Observe the gate voltages of the two MOS transistors. It can be noticed that they are reversed from each other. The yellow waveform is the gate voltage of the MOS tube above, and the cyan waveform is the gate voltage of the MOS below. You can see that the amplitude of the gate voltage of the MOS transistor above is twice that of the MOS transistor below. It should be noted here that both the operating voltage of the MOS transistor and the drive voltage of the IR2181 are 12V. So, in this case, the gate drive voltage of the above MOS transistor basically reaches about 24V. From the measurement results, the function of the IR2181s is consistent with that of the previous IR2104s driver IC. However, this measurement method can cause problems, such as parasitic inductance, which causes the signal to jitter up and down. This can be solved by adding a 10 ohm resistance to the gate input.
▲ Use a probe to measure the gate voltage signal of the MOS tube
Set the dead zone between the PWM output signals with a dead zone constant of 20, which corresponds to about 33ns. It can be seen that the gate voltage of the lower tube is about 33ns behind that of the upper tube, and the waveform oscillation is also reduced. The same is true for the rising edge. At this point, a slight reduction in the operating current of the circuit is observed. That's about 2mA less than when there were no dead zones. The upper and lower MOS transistor gate voltage waveforms are now shown with no dead zones. At this time, there is a certain leakage current corresponding to the simultaneous conduction of the upper and lower tubes.
※Summary※
In this paper, the MOS tube half-bridge drive circuit IR2181s is tested, which has two inputs, high and low outputs. In this way, the appropriate dead time can be set in the PWM module of the microcontroller to ensure that the upper and lower MOS transistors can avoid pass-through. Later, based on these preliminary test results, the half-bridge power circuit was designed.