Akai VS-X9EGN

Until t = tl is reached, “ic” climbs up proportionally
to the passage of time under the influence of “‘ib’’,
but since “ic”? cannot exceed hFE.ib in level, Vb as
well as “ib”? will drop down to a zero level at the
point in time tl when the linearity of ‘‘ic”’ is lost.
At that time, since ib = 0, ‘‘ic” will also drop down to
a zero level, and TR1 will turn off.
During the interval in which TR1 remains on (tO to
tl), no current flows through the secondary coil of
transformer TI due to the reverse biased D8. See
Fig. 8-4.
Fig. 8-4
2) TRI: OFF MODE
Because TRI sharply turns off at tl, a voltage with
the illustrated polarity will then be induced in coil
Lp. See Fig. 8-5.
Collector voltage VCE of TR1 at that time will be:
VCE=V+Vp
Meanwhile, for overvoltage preventive purposes, TR1
has been provided with a snubber (composed of DS,
R4, and C7). See Fig. 8-6.
In secondary coil Ls of transformer T1, a voltage with
the illustrated polarity will be generated to flow
current “‘is’”’ through Ls. See Fig. 8-5.
vs = Vout + VD8 = Vout
The “‘is” waveform will slope down rightward. See
Fig. 8-7.
Tl is 08
Vs cl2
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<
ao]
VCE
Fig. 8-6
is
t
0 ti t2
TRI ———ON —ste OFF —S<— ON —>
Fig. 8-7
During the interval in which TR1 remains off,
voltage ‘“‘vb” is generated in coil Lb and its magni-
66397
tude proportional to the current “‘is’’ slope (i.e.
vb = Mbs a), Current “ib” will be flown by “vb”
to charge capacitor C6. See Fig. 8-8.
At t=t2, since “is” drops down to a zero level
(Fig. 8-7), voltage “vb” will also drop down to zero.
Then, as soon as vb = 0 is reached, C6 will begin to be
discharged. See Fig. 8-9.
The discharge current will again flow a base current
through TR1 which will therefore turn on.
The cyclic repetition of the above steps sustains an
oscillatory behavior of the circuit.
Vout
Fig. 8-8
Fig. 8-9
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