9-17
2-2 Hor Drive Circuit
As mentioned in section of Deflection circuit, the switching-
over between duty ratio of drive pulse and base current is
necessary. In High Voltage circuit, more severe condition is
added.
In Fig. 21, solid line shows current waveform of output
transistor of High Voltage circuit, and dotted line shows
current waveform of output transistor of Deflection circuit.
Comparing these, the damper period TD’ is short, because
transistor of High Voltage circuit has small a.c. element but
it has large d.c. element.
By this reason, in high voltage side, discontinuous
phenomenon tends to happen: (The phenomenon that
continuity of current is lost because base current is not
supplied to hor output transistor even though damper period
finishes.) This phenomenon tends to happen because d.c.
element becomes large by decreasing of power voltage under
lower frequency and results in short period of damper.
Therefore, it is necessary that in high voltage side, period of
base current flowing is made long. Damper period TD
becomes long, because d.c. element exists little in Deflection
side.
Because drive pulse is commonly used in High voltage side
and in Deflection side, this duty ratio is controlled to be fit in
High voltage side. Specially, it is necessary that duty ratio is
largely changed, so that the period of base current flowing is
made long in low frequency mode.
To change amount of base current, switching-over operation
of voltage which is applied to primary of drive trans, is done
as in Deflection circuit. But the base current is set to smaller
value than in Deflection circuit, as much as collector current
of output transistor is small.
TD'
TD
Id
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