Figure 1- 1

As shown in the above figure, the booster circuit has two working processes: charging process and discharging process. Firstly, the boost circuit is designed on multism as follows:

Charging process:

When the switch tube is turned on, the input current flows through the inductor, and the energy is transferred from the input DC power supply to the inductor, and the two tubes are reversed, and no energy is transferred to the output end.

The following waveform, red is the inductance current, and purple is the voltage value of the switching node SW.

Figure 2 PWM and inductor current waveforms

From the above waveform analysis, it can be seen that when the switch tube is opened, the loop of Ton is taken away, and at this time, the DC power supply charges the inductor, and the inductor current rises linearly.

According to the purple SW node voltage waveform analysis:

When the switch tube is open, Vsw=0.5V

When the switch tube is closed, VO+VD = 8.4V V.

Analyze the voltage across the inductor when the switch tube is turned on;

The voltage difference across the inductor is vin-vsw = 4-0.5 = 3.5v.

The voltage difference across the diode is v0-VSW = 7.2-0.5 = 6.7V. At this time, the diode is reversed to prevent the capacitor from discharging to the ground.

When the switch tube is turned on, the load is mainly supplied by the capacitor, because the voltage of the capacitor cannot change suddenly! !

Discharge process

When the switch is turned off, the inductive energy storage is transmitted to the output terminal (through the diode), but part of the energy at the output terminal comes directly from the input DC source (note the difference with the switch tube, the load is only powered by the capacitor when it is turned on, and the DC source charges the capacitor and supplies power to the load when it is turned off).

Because the current of the inductor will not change suddenly, when the switch tube is turned off, the current will not change suddenly, but will change from the original current to 0 with a certain slope.

Analysis of output capacitor current

As shown in the above figure, the following waveform is the output voltage waveform of the capacitor. According to the analysis, the current of the capacitor is chopped (in fact, it is chopped in all topologies because the diode current composed of the output capacitor current and the load current is chopped).

From the above waveform analysis, the discharge current of the capacitor is 9.05mA, and the diode, capacitor and load current are further measured. It is known that when the switch tube is closed, the DC power supply (DC power supply+inductor) charges the capacitor while supplying power to the load.