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This article describes a stepdown DC-to-DC (or buck) converter in which the switching transistor is referenced to ground.
English (United States)
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Buck Converter With Switch Referenced to Ground
This article describes a stepdown DC-to-DC (or buck) converter in which the
switching transistor is referenced to ground.
In a conventional buck converter, the switch transistor is not referenced to
ground, making it difficult to provide proper transistor drive voltages. Different
approaches have been used in an effort to overcome drive problems. In a ``level
shifting'' approach, a control circuit which is referenced to ground is used to drive
a high voltage PNP transistor which, in turn, drives the switch transistor in the
buck converter. The drawbacks to this approach are the high power dissipation
levels, the requirement for an expensive high voltage PNP transistor, and the
difficulty of achieving negative off drive.
In a ``transformer drive'' approach in a conventional buck converter, a pulse
transformer is used to drive the base of the switch transistor. For large variations
of bulk voltage, the required ratio may make it difficult or impossible to reset the
transformer each cycle. Also, pulse transformers tend to be expensive.
In the buck converter disclosed in the drawing, the control circuit and the
switch transistor are both referenced to ground while the output voltage Vo is
referenced to the bulk voltage Vb. When the switch transistor Q1 is driven on by
control 10, current is supplied to load 12 while capacitor 14 charges and energy
is stored in inductor 16. When Q1 is on, diode 18 is backbiased. When swi...