BUCk DC/DC converter control module design ideas

The DC chopper circuit experiment includes two basic chopper circuits: step-down chopper circuit and step-up chopper circuit. Figure 1 shows the schematic diagram of the step-down chopper circuit.

The basic principle of the step-down chopper circuit is: when the switch V is on, the power supply F supplies power to the load, the load voltage uo=E, and the load current rises according to an exponential curve; when V is off, the load current continues to flow through the diode VD, the load voltage 1/0 is approximately 0, and the load current decreases according to an exponential curve. In order to make the load current continuous and with small pulsation, the value of the series inductor L is usually larger, and the average value of the load voltage is:

Figure 1 Schematic diagram of step-down chopper circuit

Figure 2 shows the schematic diagram of the boost chopper circuit. When analyzing the working principle of the boost chopper circuit, first assume that the inductance L in the circuit is very large, and the capacitance C is also very large. During the period when V is in the on state, the power supply E charges the inductance L. The charging current is basically constant at I1, and at the same time, the voltage on the capacitor C supplies power to the load R. Because the C value is very large, the output voltage uo is basically kept constant, recorded as Uo.

Figure 2 Schematic diagram of boost chopper

Assume that the time V is in the on state is tON, and the energy accumulated in the inductor L is EI1ton. When V is in the off state, E and L charge the capacitor C together and provide energy to the load R. Assume that the time V is in the off state is toff, and the energy released by the inductor L during this period is (UO-E)I1toff° When the circuit works in a steady state, the energy accumulated by the inductor L in a cycle T is equal to the energy released, that is:

The output voltage of the boost chopper circuit is higher than the power supply voltage.

The function that the control circuit needs to achieve is to generate a PWM signal, which is generated by the PWM module of PIC16F877 to control the on and off of the main power device in the chopper circuit, and to achieve the purpose of controlling the output voltage by adjusting the duty cycle α. In addition, the control circuit also completes certain protection functions.