What Is a Buck Converter?

The DC / DC converter is a voltage converter that effectively outputs a fixed voltage after converting the input voltage. DC / DC converters are divided into three categories: step-up DC / DC converters, step-down DC / DC converters, and step-up and step-down DC / DC converters. Three types of control can be used according to demand. The PWM control type has high efficiency and good output voltage ripple and noise. The PFM control type has the advantage of low power consumption even when it is used for a long time, especially when the load is small. The PWM / PFM conversion type implements PFM control at small loads, and automatically switches to PWM control at heavy loads. At present, DC-DC converters are widely used in mobile phones, MP3, digital cameras, portable media players and other products. It is a chopper circuit in terms of circuit type classification.

DC-DC converter

The DC / DC converter is a voltage converter that effectively outputs a fixed voltage after converting the input voltage. DC / DC converters are divided into three categories: step-up DC / DC converters, step-down DC / DC converters, and step-up and step-down DC / DC converters. Three types of control can be used according to demand. The PWM control type has high efficiency and good output voltage ripple and noise. The PFM control type has the advantage of low power consumption even when it is used for a long time, especially when the load is small. The PWM / PFM conversion type implements PFM control at small loads, and automatically switches to PWM control at heavy loads. At present, DC-DC converters are widely used in mobile phones, MP3, digital cameras, portable media players and other products. It is a chopper circuit in terms of circuit type classification.

Chinese name

DC-DC converter

Foreign name

Direct current-Direct current converter

Classification

Boost, Buck and Buck-Boost

nickname

Switching power supply or switching regulator

Constitute

Diodes, transistors, capacitors, etc.

What is DC (Direct Current)? It refers to a DC power source, such as a dry battery or a car battery. The 220V power supply for household use is alternating current (AC). If a DC voltage (3.0V) can be converted into another DC voltage (1.5V or 5.0V) by a converter, we call this converter a DC-DC converter, or a switching power supply or switching regulator. .

A: The DC-DC converter is generally composed of a control chip, an inductor, a diode, a triode, and a capacitor. When discussing the performance of a DC-DC converter, if it is only for a control chip, it cannot be judged for its merits. The characteristics of the components of the peripheral circuit and the wiring method of the substrate can change the performance of the power supply circuit. Therefore, comprehensive judgment should be made.

B: modulation method

1: PFM (Pulse Frequency Modulation)

The switching pulse width is constant, and the output voltage can be stabilized by changing the frequency of the pulse output.

2: PWM (pulse width modulation)

The switching pulse frequency is constant, and the output voltage can be stabilized by changing the pulse output width.

C: In general, the performance differences of DC-DC converters using two different modulation methods, PFM and PWM, are as follows.

Selection of PWM frequency and PFM duty cycle.

The DC-DC circuit design must consider at least the following conditions:

1. The range of external input power supply voltage and the output current.

2. DC-DC output voltage, current, system power maximum.

Considering the choice of PWM IC based on the above two points:

1. Maximum input voltage of PWM IC.

2. The frequency of PWM switching. The choice of this point is related to the efficiency of the system. The choice of the size of the energy storage inductor and capacitor also has a certain impact.

3. The maximum rated current that the MOS tube can withstand and its rated power. If the DC-DC IC has a built-in MOS, you only need to consider the rated current output by the IC.

4. MOS switching voltage

2. Diode: Schottky diodes are usually used. The reverse voltage and forward current should be considered when selecting. Generally, the reverse voltage is twice the input power voltage and the forward current is twice the output current.

3. Capacitor: The selection of capacitor is based on the switching frequency, system ripple requirements and output voltage requirements. The capacitance and the equivalent resistance inside the capacitor determine the magnitude of the ripple (of course, it is also related to the inductance). ^[1]

The DC-DC converter powers the various circuits in the entire system. Although each circuit may perform well on the test bench, the overall performance of the system often does not reach the performance effect of each circuit. Why? There are many potential factors, and the overall grounding system of the various circuits in the system is the primary reason. The designer needs to be very clear about how each circuit is grounded and if there is a ground loop in the system.

A ground loop is formed when more than one ground connection exists between two circuits and / or systems. Repeated ground channels are equivalent to forming a receiving interface

Figure 1 Typical ground loop

Due to the voltage difference between the instruments, the signal in the interconnecting wires will add this voltage difference to the signal, causing a "acoustic" voltage in the wires. This is one reason why 60 Hz noise (or horizontal interference in the video signal) is heard in the audio signal. Another problem is the current flowing in the signal cable ground. This current can also flow into cables and equipment. Designers always pay attention to the grounding of the ground, but often do not optimize the design, thereby eliminating the sensitivity of the noise floor. Therefore, it is the most basic requirement to ensure that the ground loop current does not cause problems in the system when properly designing the ground circuit inside the system.

As another example, a ground loop is a common problem when multiple audio-visual system components are connected together. Common noise in audio systems is often caused by ground loop problems. In addition, the audible "acoustic sound" is also a typical ground loop problem (of course, this depends on the frequency of the AC power supply voltage used in the country). Of course, the most common example of a ground loop problem is when the system uses an instrument connected to an outlet, while another instrument is connected to a different grounded outlet elsewhere in the room.

Ground the system to avoid ground loops.