INVERTING BUCK-BOOST CONVERTERS

Inverting Buck-Boost Converters

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Inverting Buck-Boost Converters

An inverting buck-boost is a type of switch-mode power supply (SMPS) that converts an input voltage into a higher or lower output voltage. It is given the name inverting because it generates a negative output voltage.

The basic schematic of a inverting buck-boost converter. SW1 is typically a MOSFET switched by control logic (not shown).

The basic schematic of a inverting buck-boost converter. SW1 is typically a MOSFET switched by control logic (not shown).

Output Voltage

Again, the output voltage for an ideal SEPIC is purely determined by the input voltage and the duty cycle \(D\), as given in the following equation:

\begin{align} V_{OUT} = -\frac{D}{1 - D} V_{IN} \end{align}

To give you an idea of how varying the duty cycle can produce either a higher or lower output voltage, see the below image which shows how the output voltage can vary from a small fraction of \(V_{IN}\) to many times larger than \(V_{IN}\), and they are equal when the duty cycle is set at 50%.

Relationship between duty cycle and the voltage ratio for a inverting buck-boost converter, ignoring the sign (so applicable for a SEPIC also). Dotted line drawn where `\(V_{OUT} = V_{IN}\)`, at `\(D=0.5\)`.

Relationship between duty cycle and the voltage ratio for a inverting buck-boost converter, ignoring the sign (so applicable for a SEPIC also). Dotted line drawn where \(V_{OUT} = V_{IN}\), at \(D=0.5\).

As the duty cycle approaches 100%, the ideal output voltage approaches infinity! In practise, non-idealities and component absolute maximums limit the the output voltage to something in the range of 10x the input voltage.

References


Authors

Geoffrey Hunter

Dude making stuff.

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