DC-DC circuit design skills and device selection principles
DC-DC refers to direct current (Direct Current). It is a device that converts electrical energy of one voltage value into electrical energy of another voltage value in a DC circuit. For example, a DC voltage (5.0V) can be converted into other DC voltages (1.5V or 12.0V) through a converter. We call this converter a DC-DC converter, or switching power supply or switching adjustment Device.
The DC-DC converter is generally composed of a control chip, an inductor, a diode, a transistor, and a capacitor. When discussing the performance of DC-DC converters, if you only focus on the control chip, you cannot judge its pros and cons. The component characteristics of the peripheral circuit and the wiring method of the substrate can change the performance of the power circuit. Therefore, a comprehensive judgment should be made.
The use of DC-DC converters is conducive to simplifying the design of power circuits, shortening the development cycle, and achieving the best indicators. It is widely used in power electronics, military industry, scientific research, industrial control equipment, communication equipment, instrumentation, switching equipment, and access equipment, Mobile communications, routers and other communications fields and industrial control, automotive electronics, aerospace and other fields. With the characteristics of high reliability and easy system upgrade, the application of power modules is becoming more and more extensive. In addition, DC-DC converters are also widely used in products such as mobile phones, MP3s, digital cameras, and portable media players. It belongs to the chopper circuit in the circuit type classification.
Its main feature is high efficiency: Compared with the LDO of a linear regulator, high efficiency is a significant advantage of DCDC. Usually the efficiency is above 70%, and the high one can reach above 95% under heavy load. The second is to adapt to a wide voltage range.
A: Modulation method
1: PFM (Pulse Frequency Modulation Method)
The switching pulse width is constant, and the output voltage is stabilized by changing the frequency of the pulse output. Even if the PFM control type is used for a long time, especially when the load is small, it has the advantage of low power consumption.
2: PWM (pulse width modulation method)
The frequency of the on pulse is constant, and the output voltage is stabilized by changing the pulse output width. The PWM control type has high efficiency and good output voltage ripple and noise.
B: Under normal circumstances, the performance differences of DC-DC converters using PFM and PWM, which are two different modulation methods, are as follows.
The selection method of PWM frequency and PFM duty cycle. The PWM/PFM conversion type implements PFM control when the load is small, and automatically switches to PWM control when the load is heavy.
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