Inverting Buck-Boost Converters

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.

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%.

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