Design regulated power supply, BUCK circuit and control circuit according to the design task of step-down chopper circuit. The BUCK circuit is used to generate the falling music chopper circuit. The control signal generated by the control circuit is transmitted to the BUCK circuit, so that the signal is added to the switch control terminal, and it can be turned on or off. Control the main circuit of the meter-down chopper circuit by controlling the on and off of the switch.
Basic principle of Buck converter:Buck circuit is a step-down chopper circuit, which is one of the DC chopper circuits, 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 a direct DC-DC converter. One of the typical uses of a step-down chopper circuit is to drive a DC motor, which can also be loaded with a battery.
As shown in the figure below, a fully-controlled switching device Q is used in the circuit. The switching tube Q is driven by the switching pulse signal. The pulse signal comes from the pulse signal control circuit. The period T of the pulse signal remains unchanged, and the pulse width ton can be changed. Then the duty cycle of conduction can be adjusted to change the output power. In order to provide a channel for the inductor current in the load when the switch is turned off, a freewheeling diode D is set. When the transistor is turned on, if the saturation voltage drop is ignored, the output power UO is equal to the input voltage: when the transistor is turned off, if the leakage current of the transistor is ignored, the output voltage is 0. The main circuit 1. Make the waveform as shown in the figure.
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, and the voltage from the rectifier circuit contains large ripples, and the voltage quality is not very good, so it needs to be filtered. This circuit uses RC filter. Because the ratio of the capacitor-filtered DC output voltage UO to the secondary side voltage U2 of the transformer is relatively human, and it is suitable for circuits with small currents and relatively large rectifier currents. Therefore, the capacitor filter used in this circuit. Because this circuit requires a stable output, it also needs to use a regulator_pole tube for voltage stabilization.
Drive circuit design
The following figure shows a gate drive circuit composed of a pulse transformer. 1. The principle is that the forward driving signal makes VI1 turn on, the power supply voltage acts on the primary side of the pulse transformer, and the second and second voltage acts on the ICBI through the diodes VD2, VD3 and the gate resistor to make ICBI turn on. Transistor VT2 hesitates to reverse-bias the base and truncates.
When the drive signal is zero, VI1 will stop at i. The primary 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 transformer is added to the pole tube VD2.E via R2. The charge on the IGBI gate junction capacitor 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 drive circuit, and the drive circuit has a simple structure. When the pulse changes, the drive voltage amplitude is unchanged, and it can be used to drive ICBI 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%.
Parameter setting of each part
The components that need to determine the parameters in the main circuit include IGBT, diode, DC power supply, inductance, capacitance, and resistance value determination. The parameter determination process is as follows. In this design process, the I. operating frequency is set to 100kHz.
(1) Power supply
Because the problem requires the input voltage to be about 36V, the input voltage value is obtained through the rectifier circuit. (2) Heart resistance
Because when the output voltage is 12V, the output current is 3A, and the negative I resistance can be obtained as RL=Uo/Io=4Q. (3) IGBI
When the IGBT is turned off, the loop continues to flow through the pole tube. At this time, the maximum positive voltage on both ends of the IGBT is 36V: when = 1, ICBI has the maximum current, which is 3A. Therefore, it is necessary to set the maximum continuous current of the IGBT collector Ic>3A, and the reverse breakdown voltage Bvceo>36V.
(4) Diode
When =1, it bears the maximum back pressure of 36V; when it approaches 1, its maximum current is close to 3A, so it is necessary to set the diode rated voltage to be greater than 36V and the rated current to be 3A.
Problems encountered in the design process and troubleshooting measures:
(1) I am unfamiliar with the concept of DC chopper circuit, and I feel unable to start, and I understand the principle after reviewing 15 related books.
(2) I don't know how to calculate and select some relevant parameters of the BUCK converter (for example, choose Lf and Cf). After going online: query relevant knowledge and discuss and analyze with students, and finally determine the parameters selected for the relevant originals after calculation.
(3)-: At the beginning of the design, the drive control circuit was not involved, but later I found that I had ignored this block. (4) Through checking the information, I know the types of various drive circuits, and finally according to the design requirements of the course and the actual situation, considering that the frequency requirement is 1khz as a high-frequency circuit, and the duty of the chopper circuit is relatively small, so I choose to use discrete components The drive circuit is composed.
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