I. There are three common architectures of DC-DC:
- Buck (step-down DC/DC converter)
- Boost (step-up DC/DC converter)
- Buck-Boost (step-up and step-down DC/DC converter)
II. A DC-DC converter is generally composed of a control chip, inductance coil, diode, triode, and capacitor.
III. Main parameter references for DC-DC chip selection:
- When selecting a DC/DC, the input and output voltages, output load, efficiency, cost, packaging, and switching frequency should be considered first to meet the application. Special applications also need to consider static power consumption (such as for handheld devices), standby power consumption, etc.
- Input voltage range (Input Voltage): Consider the range of actual input voltage fluctuations and select according to the recommended working voltage range in the DC/DC device manual to ensure that it does not exceed the device specifications.
- Output voltage (Vout): The output voltage is a very important parameter of DC/DC, and it is also the first parameter that electronic equipment designers should consider when selecting. DC/DC has two types: fixed output voltage and adjustable output voltage.
- Maximum output current (Max Current): The continuous output current capability is an important parameter of DC/DC devices. When selecting, this parameter should be referred to and a certain margin should be reserved. The selection of the output current parameter of DC/DC needs to evaluate the instantaneous peak current and heat generation of the subsequent circuit, and determine it comprehensively and meet the derating requirements (generally, 80% derating should be met, that is, if 2A is actually required, at least 2.5A and above current output capability DCDC should be selected).
- Ripple noise (Ripple): The switching action of DC/DC devices and the charging and discharging of inductors and capacitors will cause problems such as EMI (electromagnetic radiation/interference) and large power supply ripples. If the ripple of the DC/DC device is large, it will directly affect the conversion efficiency of the device, affect the instability of the system operation, have a relatively high heat generation, and make the power consumption of the entire system relatively large. Regarding the index that can be achieved for ripples depends on the design of the power supply itself, and at the same time, it needs to consider the actual needs of the power supply system with load, that is, to pay attention to the ripples under light load and heavy load. The ripple value of each output load of the power supply is related to the current value of this road. The power supply generally will not exceed this range under light load. The power ripple of DC/DC power supply generally should be below 200mV to 50mV, and it cannot exceed this range under full load. In actual use, most digital chips with high requirements have a 5% ripple requirement. For small-signal analog circuits, the power supply ripples are extremely demanding. Generally, it is required to be 50mV or even lower. At this time, linear power supply may need to be considered. High-speed and high-precision data acquisition systems have relatively high requirements for accuracy and speed, and are extremely sensitive to the ripple noise of the power supply. In addition to requiring small power supply ripple noise, it is also necessary to select some operational amplifiers with high precision, common mode, and large power supply suppression ratio to cooperate. The ripple noise of the power supply generally needs to be controlled within 10mV.
- Switching frequency (Switching Frequency): DCDC generally has a working frequency of several hundred K to several M. The switching frequency determines the selection of the external inductance. The larger the frequency, the relatively smaller the required inductance value, saving the area of the circuit board. The larger the external inductance, the better the suppression effect on ripples. The disadvantage is that it cannot quickly respond to changes in the load.
- Efficiency (Efficiency): DC/DC devices have a relatively high conversion efficiency, and will not cause excessive heat energy loss and heat dissipation problems in high-power power conversion. At the same time, it is necessary to pay attention to both light load and heavy load. Under light load, it will affect the standby power, and under heavy load, it will affect the temperature rise. Generally, it should be able to reach more than 80%.
- Load regulation (Load Regulation): Changes in the power load will cause changes in the output voltage of the power supply. When the load increases, the output voltage decreases; conversely, when the load decreases, the output voltage increases. A good power supply has a smaller output change caused by load changes, usually with an indicator of 3%-5%. Load regulation is an indicator to measure the quality of the power supply. A good power supply has a smaller voltage drop when the output is connected to the load.
IV. Applications of DC-DC:
The use of DC-DC converters is beneficial to simplifying the design of the power supply circuit, shortening the development cycle, and achieving the best indicators, etc., and is widely used in power electronics, military industry, scientific research, industrial control equipment, communication equipment, instrument and meter, switching equipment, access equipment, mobile communication, routers, and other communication fields and industrial control, automotive electronics, aerospace, and other fields.
It has the characteristics of high reliability and easy system upgrade, and the application of power modules is becoming more and more widespread. In addition, DC-DC converters are also widely used in products such as mobile phones, MP3, digital cameras, portable media players, etc. In terms of circuit type classification, it belongs to chopping circuit.
Its main features are high efficiency: Compared with the LDO of the linear regulator, high efficiency is a significant advantage of DC-DC. Usually, the efficiency is above 70%, and the efficiency can reach above 95%. Secondly, it has a wide range of adaptable voltages.