Design principle:
Buck circuit is the step-down chopper circuit, which is a kind of DC chopper circuit, and the boost chopper circuit constitutes the two most basic circuits of the DC chopper circuit. The function of the DC chopper circuit is to change the direct current into another-fixed Voltage or adjustable voltage direct current, also known as direct direct current direct current converter. One of the typical uses of a step-down chopper circuit is to drive a direct current motor, and it can also be loaded with a battery.
Rectifier circuit design
This design adopts bridge circuit rectification: a full bridge rectifier circuit is composed of four diodes. Perform Fourier transform on the rectified voltage so that the voltage from the rectifier circuit contains relatively human ripples,
The voltage quality is not very good, so it needs to be filtered. This circuit uses RC filter. Because the ratio of the point-flow output voltage UO of the capacitor filter to the secondary voltage U2 of the transformer is relatively human, and it is suitable for the circuit with small current and relatively human inrush current of the rectifier tube. Therefore, the capacitor filter used in this circuit. Because this circuit requires a stable output, a voltage stabilizer diode is also needed for voltage stabilization.
Drive circuit design
A gate drive circuit composed of a pulse transformer. Its I. The principle is that the forward drive signal makes VI1 turn on, the power supply voltage acts on the secondary side of the pulse transformer, and the secondary voltage acts on the IGBT through the diodes VD2, VD3 and the gate resistor to make the ICBT turn on. Transistor VT2 hesitates to reverse-bias the base and truncates.
When the drive signal is zero, VI1 cuts off i:--The secondary excitation current decays rapidly through VD1 and VS, so that the magnetic flux of the pulse transformer returns to zero during the pulse gap. The reverse voltage on the secondary side of the instrument I is added to the diode VD2 via R2. The charge on the IGBT gate junction capacitance is discharged through Rg and VT2, and R2 is the bias current resistance of T2.
The advantages of this circuit: This circuit does not need an independent driving circuit, and the driving circuit has a simple structure. When the pulse changes, the driving voltage amplitude is unchanged, and it can be used to drive IGBTs of various capacities.
Disadvantages of this circuit: there is no reverse voltage of the gate when it is off, and the anti-interference ability is not strong. This kind of circuit is suitable for driving high frequency occasions where the duty cycle is less than 50%.
Boost main circuit design
Boost circuit working principle
When the switch S is at the position a, as shown in Figure 5, the current ir flows through the inductor L, the current increases linearly, and the electrical energy is stored in the inductor L in the form of magnetic energy. At this time, the capacitor C discharges, R flows through the heart current I. Both ends of R are the output voltage V. The polarity is positive and negative. Since the switch tube is turned on, the anode of the diode is connected to the cathode of V. The diode bears the reverse voltage, so the capacitor cannot be discharged through the switch tube. When the switch S is switched to the position b, the circuit is formed as shown in 2(b). The magnetic field in the coil L will change the polarity of the voltage across the coil L to keep i unchanged. In this way, the voltage Vz converted into the magnetic energy of the coil L is connected in series with the power supply V. The voltage supplies power to the capacitor C and the load R. Higher than V. When the capacitor has a charging current; when it is equal to V., the charging current is zero; when V. When there is a tendency to step down, the capacitor discharges to the load R, maintaining V. constant.
Function of each component
Q switch tube IGBI.
The D Russian flow diode prevents the center circuit of c from flowing through Q at T... L open-voltage inductance plays the role of energy storage and voltage increase. C output filter capacitor, which plays the role of energy storage.
Waveform at each point of the circuit
Analysis of Continuous and Discontinuous Inductance Current
Main circuit parameter analysis
The components that need to determine the parameters in the main circuit include IGBT, diode, DC power supply, inductance, and resistance value determination. The parameter determination process is as follows.
(1) For the power supply, the input voltage is required to be 10-30V, and it is continuously adjustable. The design of its DC stabilized power supply module has been completed in front. Therefore, the DC power supply is used as the system power supply.
(2) For resistance, because when the output voltage is 75V, the output current is 0.1-1A. So by Ohm Ding
The available load resistance value is R_Uo-Em, and the available circuit resistance should be 15-1500.
(3) For the choice of ICBT, it is easy to know from Figure 4 that when the IGBT is off, the loop will continue to flow through the pole tube. At this time, the ICBT both ends can withstand the maximum positive voltage of 30V; and when a=1, the IGBT has the maximum current , Its value is 1A. Therefore, it is necessary to select an IGBI with the maximum continuous current of the collector Ic>1A and the reverse mains voltage Bvceo>30V. The general IGBT basic, t. can meet this requirement.
(4) For the choice of pole tube, when a=1, it can withstand the maximum back pressure of 30V; when a approaches 1, its withstand maximum current approaches 1A, so it is necessary to select a rated voltage greater than 30V, A pole tube with a rated current greater than 1A.
(5) In addition to selecting IGBTs and diodes, the design of the main circuit also needs to determine the parameters of the inductance, but the calculation of the inductance parameters is very complicated. The inductance is not calculated here, and the inductance value L is considered to be very hot.
Related Links Principles of DC PWM Converter Basic Structure of DC PWM Converter Circuit
