Inverting Single Inductor Buck & Boost

V IN V IN I SWITCH I SWITCH I LOAD I LOAD V OUT V OUT Function: Inverting (negative output from positive input, -V
OUT can be greater than or less than V
Function: Step-up and step-down
IN )
When to use: This topology is an alternative to sepic and flyback topologies when automatic step-up/step-down functionality is needed, but no transformer or second inductor is required
When to use: When an inverted, regulated output is needed. This topology is commonly used for output currents from approximately 300 mA to 5 A.
Characteristics: A second switch and output diode are added, resulting in an effective overlapped boost topology on top of a basic buck topology. If desired, synchronous rectification can be implemented to increased efficiency (both diodes may be replaced by FETs).
Characteristics: Easy to implement, single output
Devices to use: Any buck integrated regulator or controller (see National’s App Note AN-1157 for implementing with a SIMPLE SWITCHER® buck regulator)
Devices to use: Any integrated buck regulator or controller, including SIMPLE SWITCHER buck regulators
Comments: Alternatives for voltage inversion include cuk topologies (low noise) or switched capacitor converters where I
OUT Comments: Be sure to watch the voltage applied to the gate in the second FET which will be V is less than 200 mA (no inductor needed)
IN . If V
IN is too high for the selected FET specifications, use voltage limiting circuitry.

Push-Pull Current-Fed Push-Pull (Cascaded)

I LOAD V IN I LOAD V V OUT IN V OUT Function: Isolated step-down, step-up or buck-boost and multiple outputs
Function: Isolated step-down, step-up, or buck-boost topologies. Can do tightly regulated multiple outputs.
When to use: When isolated, medium-to-high power conversion is needed (25 W to 1000 W). This topology can also be used when the input voltage range is very wide or when the V
When to use: When isolated medium- to high-power conversion is needed,but reduced losses, high efficiency, and no output inductor are also desired.
IN /V
OUT ratio in step-down applications requires a very small duty cycle (and thus might yield poor regulation) if a standard buck topology is used.
Characteristics: The current-fed cascaded topology consists of a buck regulation stage followed by a push-pull isolation stage. Because the buck stage feeds continuous current to the push-pull stage, no output inductor is required.
Devices to use: LM5030 current-mode push-pull controller
Comments: The peak current and voltage stress in the switches are given by: V
Devices to use: LM5041 current-mode cascaded controller
PK = 2.6 V
IN max., I
PK = 1.56 x P
OUT /V
IN min.
Comments: To increase conversion efficiency, the use of synchronous rectification is recommended, both for the current-fed buck stage and the push-pull output stage (self-driven synchronous rectification)

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