On Fri, 03 Apr 2009 21:57:39 -0600 Hope for the Heartless
| In article
|> what are buck-boost transformers and its operation??????
| They're autotransformers. In "buck" mode, they reduce the AC voltage by
| the tap ratio. In boost mode, they increase it by the tap ratio.
Some buck-boost transformers can be wired as isolation transfermers. Those
that have TWO line voltage windings can do this. It reduces the capacity.
Suppose you have a BB transformer that has 2 120V windings and 2 12V windings.
In the usual cases, the 2 120V windings can be wired in parallel to a 120V
supply, or wired in series to a 240V supply. The 12V windings would then be
wired in parallel (for 12V) or series (for 24V) to provide a boost to 132V or
144V or 252V or 264V, or the equivalent ratio for lower voltage supplies. Or
these can be connected backwards for voltage drop.
To make an isolation transformer, the two 120V windings are kept separate.
One of them is connected to the 120V supply while the other has one or two
of the 12V windings in series for 132V or 144V. This can be reversed to
step down an overvoltage supply.
Another configuration is to wire the 12V windings backwards. This reduces
the voltage (and also reduces the capacity somewhat), or in reverse supply
can step lower voltages up. The ratio is slightly different and is a choice
for slight variations in voltage if needed. Both isolation and autotransformer
methods exist for this, too.
Yet another configuration only works in autotransformer mode that can give
yet another ratio. That involves the two 12V windings in series with each
other, but the 120V windings (whether parallel for 120V purpose or series for
240V purpose) tapping to the center of the two 12V windings.
Buck boost transformers also exist with 16V and 24V windings (for 32V and
48V when in series). Also, 240V line voltage windings exist (480V in series).
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