Inverse converter

A buck-boost converter , English inverting buck-boost converter, is in the power electronics , a form of DC-DC converter comprising a positive input voltage at a negative output voltage without galvanic isolation converts. The flyback converter is based on the inverse converter, but with otherwise the same functional principle, it has been expanded to include galvanic isolation. This elementary circuit is used as a component in the area of power supplies such as switched-mode power supplies .

Demarcation

The English Four Switch Buck-Boost Converter , in German referred to as cascaded step-down converter, is not an inverse converter, despite the similar name. It is a combination of a buck converter and a boost converter , with only one common inductance . With this topology, the polarity of the input and output voltage - in contrast to the inverse converter - is the same.

Both buck-boost topologies have in common, despite their completely different structure, that the output voltage can be smaller or larger than the input voltage. Only the inverting buck-boost converter is described below.

function

Basic circuit of an inverse converter

The adjacent circuit diagram of a supplies DC power source , a constant positive voltage U _E . The switch S , in real circuits usually in the form of a transistor realized on for the duration of t _A , the voltage on the coil with an inductance L . The current I through the coil changes by the amount:

${\displaystyle \Delta I={\frac {U_{\text{e}}\cdot t_{\text{ein}}}{L}}}$

After the duty cycle of the switch S for the duration t _of off, which remain constant switching of the current through the coil needs. Characterized that is diode D conductive and charges the capacitor to a negative potential relative to the reference voltage U _a of:

${\displaystyle -U_{\text{a}}=L\cdot {\frac {\Delta I}{t_{\text{aus}}}}}$

The cycle then repeats itself. The level of the negative output voltage can be specified by the pulse width ratio η between the two switching states:

${\displaystyle -{\frac {U_{\text{a}}}{U_{\text{e}}}}={\frac {t_{\text{ein}}}{t_{\text{aus}}}}={\frac {\eta }{1-\eta }}}$

Like any switching converter, the inverse converter can be operated in discontinuous current mode , this is the case when the current through the coil drops to 0 in one cycle, or in continuous current mode . The switching frequency depends, among other things, on the load R and the permissible ripple current .

literature

• Ulrich Schlienz: Switching power supplies and their peripherals . 3. Edition. Vieweg, 2007, ISBN 978-3-8348-0239-2 .
• Sanjaya Maniktala: Switching Power Supplies AZ . 2nd Edition. Elsevier, 2012, ISBN 978-0-12-386533-5 .