Principle of operation

AN2837

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Principle of operation

The polarity-inverting converter uses the basic principle of energy storage in the inductor L

during the ON time of the operating period (Figure 2), and then transfers the energy via the

freewheeling diode D to the output during the OFF time (Figure 3).

When the switch turns ON, the diode is reverse-biased and current flows only in the

inductor.

When the switch is turned OFF, the reverses its polarity, thus the freewheeling diode is

forward-biased, and the energy stored in the inductance is transferred to the load as well as

the capacitor.

The output voltage across the capacitor becomes negative because the inductor current is

negative with respect to ground.

This circuit is also known as a buck-boost converter because this type of converter can step-

up and step-down the magnitude of the input voltage.