Buckboost chronogram discontinuous fr. Buckboost chronogram discontinuous. Buckboost chronogram. Buckboost conventions.
Buckboost converter. Buckboost operating fr. Buckboost operating. Buckboost resistance fr. Buckboost resistance-ru. Buckboost resistance.
Conversor Boost. Convertisseur Buck Boost. Cuk converter with AC transformer. Cuk converter. Doppelinverter schalter.
In this mode Tr2 is turned off, and Tr1 is switched on and off by a high frequency square wave from the control unit. When the gate of Tr1 is high, current flows though L, charging its magnetic field, charging C and supplying the load. The Schottky diode D1 is turned off due to the positive voltage on its cathode.
Fig 3. The initial source of current is now the inductor L. Its magnetic field is collapsing, the back e. As the current due to the discharge of L decreases, the charge accumulated in C during the on period of Tr1 now also adds to the current flowing through the load, keeping V OUT reasonably constant during the off period.
In Boost Converter mode, Tr1 is turned on continually and the high frequency square wave applied to Tr2 gate. During the on periods when Tr2 is conducting, the input current flows through the inductor L and via Tr2, directly back to the supply negative terminal charging up the magnetic field around L. Whilst this is happening D2 cannot conduct as its anode is being held at ground potential by the heavily conducting Tr2.
For the duration of the on period, the load is being supplied entirely by the charge on the capacitor C, built up on previous oscillator cycles. At the start of the off period of Tr2, L is charged and C is partially discharged.
The inductor L now generates a back e. Notice particularly that the polarity of the voltage across L has now reversed, and so adds to the input voltage V S giving an output voltage that is at least equal to or greater than the input voltage. See how the Buck-Boost circuit is really just a combination of Buck and Boost mode circuits. See how the operation of the circuit in both Buck and Boost modes can be controlled by a simple control unit.
See the current paths during the on and off periods of the switching transistor in either mode. See the magnetic field around the inductor grow and collapse, and observe the changing polarity of the voltage across L. Watch the effect of ripple during the on and off states of the switching transistor. In Boost Mode see the input voltage V S L add to give an output voltage greater than the input voltage. There are a number of variations of this basic Buck-Boost circuit, some designs working at lower frequencies or at high voltages may use bipolar transistors instead of MOSFETs; at low frequencies the higher speed switching of MOSFETs is less of an advantage.
Another variation is to use synchronous switching where, instead of using diodes that simply respond to the voltage polarity across them, four synchronised by the control unit MOSFETs do all the switching. The control unit may also carry out over current and over voltage protection, as well as the normal oscillator and pulse width modulation functions to regulate the output voltage.
This reduces the overall current drawn from the typically battery supply, prolonging battery life. Buck-Boost Converter I.
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