Design of high power adjustable switching power supply

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Summary:

1 Introduction

Switching power supplies have emerged as an alternative to linear regulated power supplies, and their applications and implementations have become increasingly sophisticated. The integrated technology makes the electronic device develop in the direction of miniaturization and intelligence. The new electronic device requires the switching power supply to have smaller volume and lower noise interference, so as to achieve integration and integration. For medium and small power switching power supplies, monolithic integration is achieved, but in high-power applications, due to excessive power loss, it is difficult to make monolithic integration, and it is necessary to ensure the parameters of the power supply according to its topology. Try to reduce the size of the system.

2. Typical switching power supply design

The switching power supply is generally composed of a PWM (Pulse Width Modulation) control IC (Integrated Circuit) and a power device (power MOSFET or IGBT), and meets three conditions: the switch (the device operates in the switching nonlinear state), and the high frequency. (The device operates at low frequencies that are not close to the upper frequency) and DC (the power output is DC instead of AC).

2.1 Control IC

Take the MC33060 as an example to introduce the control IC.

The MC33060 is a high performance voltage-driven pulse width modulation device manufactured by ON Semi Semiconductor. It uses a fixed-frequency single-ended output and can operate from -40 ° C to 85 ° C. Its internal structure is shown in Figure 1 [1], the main features are as follows:

1) integrated all pulse width modulation circuits;

2) Built-in linear sawtooth oscillator, the external component has only one resistor and one capacitor;

3) Built-in error amplifier;

4) Built-in 5V reference voltage with 1.5% accuracy;

5) Adjustable dead zone control;

6) Built-in transistor provides 200mA drive capability;

7) Undervoltage lockout protection;

Figure 1 MC33060 internal structure diagram

Brief description of its working principle: MC33060 is a fixed frequency pulse width modulation circuit with built-in linear sawtooth oscillator. The oscillation frequency can be adjusted by an external resistor and a capacitor.

(2-1):

The width of the output pulse is achieved by comparing the positive sawtooth voltage on capacitor CT with the other two control signals. The output of power tube Q1 is controlled by a NOR gate, ie the output is only active during a sawtooth voltage greater than the control signal.

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