What is a chopper circuit?

Chopper circuit originally refers to "cutting off" a part of sine wave for some needs in power supply application (for example, when the voltage is 50V, the latter 50V ~ 0V part is cut off with electronic components, and the output voltage is 0. Later, the DC-DC switching power supply was used for reference, mainly because the original linear power supply was "chopped" into pieces by the line during the voltage regulation of the switching power supply.

2, chopper circuit classification

A buck circuit: buck chopper, whose output average voltage Uo is less than the input voltage ui, and the polarity of the output voltage is the same as that of the input voltage.

Step-up circuit: step-up chopper, whose output average voltage Uo is greater than the input voltage ui, and the polarity of the output voltage is the same as that of the input voltage.

C.Buck-Boost circuit: Buck or Boost chopper, whose output average voltage Uo is greater than or less than the input voltage Ui, and the polarity of the output voltage is opposite to that of the input voltage, and it is transmitted through inductance.

D Cuk circuit: step-down or step-up chopper, whose output average voltage Uo is greater than or less than the input voltage ui, and the polarity of the output voltage is opposite to that of the input voltage, and it is transmitted through a capacitor.

This paper mainly expounds the principle of boost chopper.

3. Boost circuit

The booster circuit is shown in the following figure. Assuming that the inductance L value and the capacitance C value are both large, the working principle is analyzed below.

When A and V are connected, E charges L, and the charging current is always Ii, and C simultaneously supplies power to the load. Because of the large value of C, the output voltage is always Uo, and the V connection time is Ton. At this stage, the energy stored in L is EIiTon.

When B and V are disconnected, E and L*** charge to C in the same direction to supply power to the load R. If the time bit Toff of V is set, the energy released by the inductor L at this stage is (Uo-E)IiToff.

C, if the steady state is reached, the energy stored in L and the energy released should be equal in the period T, then

Eton = (Uo-E)IiToff

Uo - E = ETon / Toff

Uo = E( 1 + Ton / Toff)

Uo = E(Ton + Toff)/ Toff = E(T / Toff)

D, because (T/Toff) is greater than or equal to 1, the output voltage of this circuit is higher than the power supply voltage, so it is called boost chopper.

E and (T/Toff) are called boost ratio, and the size of Uo can be changed by adjusting its size.