The difference between a buck regulator and a boost regulator
Function and output voltage direction
Step-down regulator
The main function of a step-down regulator is to reduce a higher input voltage to a lower stable output voltage. For example, the common 12V DC input voltage is converted into a stable output voltage of 5V or 3.3V to meet the needs of low voltage power supply such as mobile phone chargers and some chips on the computer motherboard.
Boost voltage regulator
The boost voltage regulator is to increase the lower input voltage to the higher stable output voltage. For example, in some devices that use single or multiple dry batteries (1.5V or 3V, etc.) for power supply, the voltage can be raised to 5V, 9V, etc., through the boost regulator, in order to power circuits or devices that require higher voltages, such as portable loudspeakers and some handheld measuring instruments.
Circuit structure and working principle
Step-down regulator
Basic circuit structure: The common buck regulator adopts the buck converter structure. It is mainly composed of power switching tubes (such as MOSFET), inductors, capacitors, diodes and control circuits.
Working principle: When the power switch tube is on, the input voltage charges the inductor, the inductor current rises linearly, at this time the diode is reversed off, and the load is powered by the capacitor; When the switching tube is cut off, the inductor generates a reverse electromotive force, which supplies power to the capacitor and load through the diode, and the inductor current decreases linearly. By controlling the on-off and cut-off time (duty cycle) of the switching tube, the output voltage is adjusted to keep the output voltage stable.
Boost voltage regulator
Basic circuit structure: The boost converter structure is usually used, and also includes power switching tubes, inductors, capacitors, diodes and control circuits.
Working principle: When the power switch tube is on, the input voltage is added to both ends of the inductor, the inductor current rises linearly, at this time the diode is cut off, and the capacitor is discharged to the load to maintain the output voltage; When the switching tube is off, the reverse electromotive force generated by the inductance is superimposed with the input voltage, charging the capacitor through the diode and supplying power to the load. By adjusting the on-off and cut-off time (duty cycle) of the switching tube, the output voltage can be raised and stabilized.
Application scenario
Step-down regulator
Consumer electronic devices: widely used in mobile phones, tablets, laptops and other devices. Most of the chips and circuit modules inside these devices require a variety of low-voltage levels of power supply, and the power input of the device (such as lithium battery voltage or external adapter voltage) is relatively high, and a step-down regulator is needed to meet the voltage requirements of different components.
Power adapter: Used to convert the mains to a lower DC voltage output, such as the common 220V AC mains to 5V, 9V, 12V DC voltage, for mobile phones, routers and other devices to charge or power.
Boost voltage regulator
Portable devices: For portable devices powered by low-voltage batteries (such as dry batteries, button batteries), use when some components in the device require a higher voltage. For example, some flashlights powered by a single 1.5V dry battery boost the voltage to 3V or higher with a boost regulator to provide brighter lighting.
Renewable energy system: In the solar photovoltaic power generation system, when the photovoltaic cell output voltage is low at low light intensity, the boost regulator can raise the low voltage to a voltage level suitable for subsequent circuits (such as inverters) to improve the utilization efficiency of solar energy.
Efficiency characteristic
Step-down regulator
In the process of buck, the efficiency of buck regulator is related to the difference of input and output voltage, the load current, the performance of circuit components and other factors. Generally speaking, when the difference between input and output voltage is small, the efficiency is relatively low in the case of light load (small load current), and the efficiency will be improved with the increase of load current. However, if the difference between input and output voltage is too large, the efficiency will also be reduced due to the influence of power loss (mainly the loss of components such as switching tubes and inductors).
Boost voltage regulator
The efficiency of the booster regulator is also affected by many factors. Because in the boost process, the inductor needs to store more energy to raise the voltage, and the diode will have a certain energy loss in the reverse cutoff, so in the case of low input voltage, high output voltage and heavy load (large load current), the efficiency may be greatly affected, but with the development of technology, new boost regulators are also constantly improving efficiency.
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