A buck-boost converter is a type of SMPS (Switch-Mode Power Supply) that uses the same concept of both a buck converter and a boost converter, but in one combined circuit. We take a look at the circuitry involved and outline what applications can benefit from a buck boost converter.
How does a buck-boost converter work?
The main objective of a buck-boost converter is to receive an input DC voltage and output a different level of DC voltage, either lowering or boosting the voltage as required by the application. The design of a buck-boost converter is similar to a buck converter and boost converter, except that it is in a single circuit and it usually has an added control unit. The control unit senses the level of input voltage and takes appropriate action on the circuit based on that voltage.
If you need a quick review of how an SMPS works or how buck and boost converters are designed, check out this article: How Does a Switch-Mode Power Supply (SMPS) Work?and this article: Types of Switching DC to DC Converters.
Figure 1 shows a typical 4-switch buck-boost circuit. The diagram only shows two switches, however, the two diodes on the circuit also act as switches (since only forward voltage can get through). The control unit is usually either a PWM and control or an oscillator to control the switches. The switches can either be BJTs or MOSFETs depending on your design. If you’re dealing with low frequency, you’ll want to use a BJT, whereas if you’re dealing with high frequency, then MOSFET is the way to go. The diodes can also be different variations depending on your design, but a diode with low forward voltage and capable switching at high speeds would be your best bet.
What Are Examples of Buck-Boost Converter Applications?
Buck boost converters make it easy to modulate voltage for a wide variety of popular applications including consumer electronics, power amplifiers, self-regulating power supplies and control applications.
A buck boost application is best explained in terms of a battery powered system. Let’s say that the system has no charge and you only have a certain amount of voltage to charge up the system. The “boost” portion of the buck-boost converter is used to make the input voltage produce an output voltage that is greater than the input voltage. This allows the max voltage to charge the system as quick as possible.
As the charge of the system reaches its max capacity, however, you run the risk of overheating. This is where the “buck” portion of the buck-boost converter then recognizes that the charge of the system is getting close to full, and lowers the voltage gradually. Once the system reaches max charge, the voltage level drops to zero.
Buck-Boost Converter ICs We Like
LTC3130EMSE#PBF From Analog Devices
This buck-boost DC/DC converter is both efficient and low-noise (up to 1.2MHz Ultralow noise PWM frequency). Its input voltage can range from 2.4V to 25V, while its output voltage can range from 1V to 25V, making it very versatile.
We recommended this IC for long-life battery-operated instruments, portable military radios, low power sensors and solar panel post-regulators/chargers.
S6BP202A from Cypress Semiconductor
These buck boost converters ICs impress our applications engineers. See if they’re the right fit for your application.
This 1-channel buck-boost DC/DC converter IC has four built-in switching FETs and can supply up to 2.4A of load current within an input voltage range from 2.5 V to 42 V. It Choose from a variety of output voltages (5.000V/5.050V/5.075V/5.100V/5.125V/5.150V/5.200V) and take advantage of a wide operating frequency range from 200 kHz to 2.1 MHz.
We recommend this converter for long-life battery-operated instruments, portable military radios, low power sensors and solar panel post-regulators/chargers.
MC34063ECN from STMicroelectronics
The MC34063 has an output switch current in excess of 1.5 A and can operate from 3 V to 40 V. It also has a frequency operation all the way up to 100 kHz.This device contains an internal temperature compensated reference, comparator, duty cycle controlled oscillator with an active current limit circuit, driver and high current output switch. Output voltage is adjustable through two external resistors with a 2% reference accuracy for applications that require extra precision.
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