Note: Descriptions are shown in the official language in which they were submitted.
~61~ 0?7
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This invention relates to improvements in a ringing
choke type DC/DC converter for controlling in response to varia-
tions in a load, an input voltage and an environmental tempera-
ture.
The present invention will be further illustrated by
way of the accompanying drawings, in which:-
Fig. 1 is a circuit diagram showing a prior-art ringing
type DC/DC converter;
Fig. 2 is a waveform diagram showing the waveforms of
respective points when the circuit in Fig. 1 operates;
Fig. 3 is an equivalent circuit diagram of a voltage
control section of the circuit in Fig. l;
Fig. 4 is a circuit diagram of an embodiment of an
R.C.C. according to the present invention;
Fig. 5 is an equivalent circuit diagram of a voltage
control section of the circuit in Fig. ~;
Fig.s 6 and 7 are circuit diagrams of another embodi-
ments of R.C.C. of the invention;
Fig.s 8 and 9 are characteristics diagrams showing the
temperature characteristics of capacitors; and
Fig.s 10 and 11 are circuit diagrams showing still
another embodiments of R.C.C. using constant-voltage elements.
In the drawings, the same symbols lndicate the same or
corresponding parts.
Fig. 1 is a circuit illustrating a prior-art ringing
-- 1 --
~8~7
-
choke type DC/DC converter (hereinbelow referred to as an
"R.C.C.") disclosed, for example, in Fig. 6 on page 214 of TRAN-
SISTOR TECHNIQUE, issued in September, 1977 (by CQ Publication
Co., ~apan). In the drawing, numeral 1 denotes a d.c. power
source, numeral 2 denotes a transformer, the starting end of a
primary winding 3 of the transformer 2 is connected to the posi-
tive electrode of the d.c. power source 2., and the finishing end
of the primary winding 3 is connected to the collector of a tran-
sistor 4. The emitter of the transistor 4 is connected to the
negative electrode of the d.c. power source 1. Numeral 5 denotes
a starting resistor connected between the positive electrode of
the d.c. power source 1 and the base of the transistor 4, numeral
~ denotes a feedback winding of the transformer 2, the starting
end of the feedback winding 6 is connected through a series cir-
cuit of a resistor 7 and capacitor 8 to the base of the transis-
tor 4, and the finishing end of the feedback winding 6 is con-
nected to the emitter of the
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~ 26~
transistor 4. Numeral 9 denotes a diode, the cathode side
of the diode 9 is connected to the starting end of the
feedback winding 6, and the anode side of the windiny 6 is
connected to the negative electrode of a capacitor 10. The
positive electrode of the capacitor 10 is connected to the
finishing end of the feedback wincling 6. Numeral 11
denotes a Zener diode, the cathode side of the diode 11 is
connected to the base of the transistor 4, and the anode
side of the diode ll is connected to the negative electrode
of the capacitor lO. Numeral 12 denotes a secondary
winding of the transformer 2, numeral 13 denotes a diode,
the anode side of the diode 13 is connected to the
finishing end of the secondary winding 12, and the cathode
side of the diode 13 is connected to the positive electrode
of a capacitor 14. The negative electrode of the capacitor
14 is connected to the starting end of the secondary
winding 12. Numeral 15 denotes a load, which is connected
to both ends of the capacitor 14.
The operation of the R.C.C which self-excited
oscillates will be described with reference to the
waveforms of respective points at operating time in Fig. 2.
When a power switch, not shown, is now turned on, a voltage
Vin of the d.c. power source is applied through the
starting resistor 5 to the base of the transistor 4, and a
base current flows to the transistor 4. Thus, the
-- 2 --
~ ~i8;~:07
transistor 4 is turned on, and the collector current ic
flows to the primary winding 3. A voltage generated in the
feedback winding 5 by the magnetomotive force of the
primary winding 3 due to the collector current ic is
differentiated by the resistor 7 and the capacitor 8 to
become a base current of the differentiated waveform and
hence a forward base current iB of the transistor 4, and
the transistor 4 is therefore quickly saturated. Since the
voltage is applied reversely to the diode 13 for rectifying
an output as a load of the transistor 4 in this state, no
current flows, the collector current ic becomes a value
defined by the inductance of the primary winding 3, and
does not increase any more with respect to the base current
iB when the collector current becomes ic = hfe-iB, where
hfe denotes the current amplification factor of the
transistor 4. Thus, since the magnetic flux ln the corP of
the transformer 2 becomes constant, the voltages of the
respective windings are cancelled, and the transistor 4 is
rapidly shifted to an off state. When the transistor 4
becomes the off state, a voltage of reverse polarity to the
on state of the transistor 4 is generated in the windings as
a vibrating voltage by the magnetic energy stored in the
transformer 2 during the current flow. Therefore, a
voltage of the direction for turning on the diode 13 is
outputted to the secondary winding 12 at this time to
~ Z~ 7
charge the capacitor 14 and to supply a power to the load
15. Here, a voltage of reverse direction between the base
and the emitter of the transistor 4 is similarly generated
in the feedback winding 6 to charge the capacitor 8 through
the resistor 7 so that the electrode side connected to the
base of the transistor 4 becomes positive. Here, since a
variation in the magnetic flux in the core of the
transformer 2 becomes constant when the magnetic energy
stored during the on period is discharged to all the loads
of the windings, the voltages of the windings of the
transformer 2 tend to be cancelled. Here, the base current
i3 flows as a forward base current from the capacitor 8 to
the transistor 4 in response to the variation in the
voltage, and the transistor 4 again becomes on state.
Thus, the transistor 4 alternatively repeats the on state
and the off state to repeat the switching of the transistor
4, thereby continuing a self-excited oscillation.
Then, a mechanism for controlling the voltage in Fig.
1 will be described. As described above, the feedback
winding 6 generates a voltage in the direction for turning
on the diode 9 during the off period of the transistor 4 to
charge the capacitor 10. Thus, it is considered that the
voltage across the capacitor 10 is substantially
proportional to an outpllt voltage Vo and an input voltage
Vin. Therefore, the sum of the charging voltage of the
capacitor 10 and the induced voltage of the feedback
winding 6 is applied to the Zener diode 11 when the
transistor 4 is next turned on, and a Zener current
proportional to the difference between both the voltages
flows thereto. Thus, a part of the current supplied from
the feedback winding 6 to the base of the transistor 4 is
bypassed as the Zener current to control the base current
iB of the transistor 4, thereby controlling the on width of
the transistor 4 to act so that the output voltage Vo
becomes stable irrespective of the input voltage Vin and
the load 5. The operating principle of controlling the
voltage described above will be further described in more
detail with an equivalent circuit shown in Fig. 3.
Since Fig. 3 is shown for the convenience of
describing the voltage control, the capacitor 8 which does
not relate directly to the voltage control is omitted. The
base emitter junction of the transistor is represented by a
linear type in the equivalent circuit in Fig. 3 if the base
current iB flows forwardly in the transistor 4, and the
voltage V between the base and the emitter is to be
BE
represented by the following equation (1).
VBE = rBiB + VB (1)
where rB denotes the operating resistance of the transistor
4, and VB denotes a junction barrier voltage. Similarly,
if the voltage applied between the anode and the cathode
~6~2~7
of the Zener diode 11 becomes as high as the Zener voltage,
the Zener current iz flows, and the Zener diode voltage VzD
is to be represented by the following equation (2) in a
linear type.
ZD Z Z z (2)
where rz denotes the operating resistance of the Zener
diode 11, and Vz denotes a Zener voltage. Since the
equivalent circuit ofFig.3 is shown at a timing that the
transistor 4 is turned on, a feedback voltage ofVfis
generated in the feedback winding 6 in the direction as
shown in Fig 3. Further, the capacitor 10 is charged to
the voltage produced by subtracting the voltage Vfof the
feedback winding 6 by the on voltage of the diode 9 during
the off period of the transistor 4 and hence a voltage Vcf.
If the on voltage of the diode 9 is extremely low to be also
to be ignored, it is said that the charging voitage Vcf is
substantially equal to the voltage Vfof the feedback
winding 6 during the off period of the transistor 4. The
capacitor 10 has a capacitive component Cf and an impedance
component iCf~ A current flowing to the resistor 7 is
represented by if. Here, assume that the feedback current
if is branched to the base current iB and the Zener current
iz to be the state of the following equation (3),
iB = if - iz (3)
the following equation (4) is satisfied.
6~ 7
rB x iB + VB = r~iz+Vz+ - ~iZdt-vcf+rcfiz (4)
In the equation (4), - ¦izdt denotes the ripple voltage of
the capacitor 10. If rB x iB is smaller than the other
terms to be ignored and Cf is sufficiently large to ignore
1 ~
the term of -Jizdt, the equation (4) can be expressed by
the following equation (5)
VB = (rz + rcf)iz + Vz - VCf (5)
Therefore, the iz is represented by the following
equation (6) from the equation (5).
Vc f+VB-Vz
iz = - (6)
( rZ+rcf )
If the above equation is transformed in term of the Vz, the
following equation (7) is attained.
Vz = VB + VCf (rz rCf) Z
Here, when the Zener diode 11 is not turned on, iz=O.
Therefore, the equation (7) can be represented by the
following equation (8).
VZD = VB + VCf (8)
If the input voltage Vin is raised or the load 15 is
lightened so that the charging voltage Vcf increases and
-- 7 --
the VzD in the equation (8) become equal to or smaller
than Vz as below,
VZD 2 Vz (9)
the Zener current iz represented by the equation (6) flows.
Here, if the input voltage Vin is raised or the load 15 is
lightened, the feedback voltage Vf rises and the feedback
current if also increases, but since the charging voltage
Vcl also increases so that the Zener current iz increases,
the base current iB flowing to the transistor ~ is limited
by the equation (3) to shorten the on width, thereby
controlling so that the charging voltage Vcf becomes a
target value Vz.
The above description is the detailed mechanism of the
voltage control.
Since the prior-art R.C.C is constructed as described
above, if the input voltage Vin is raised, the load 15 is
lightened or the environmental temperature is lowered,
there is a problem that the oscillation of the transistor 4
becomes intermittent to cause the output voltage Vo to
become unstable. Thus, in order to stably operate the
R.C.C., it is necessary to limit the input voltage Vin, to
apply a dummy load to the load 15, to limit the
environmental temperature or to increase the value of the
output capacitor 14 so as to stabilize the output even if
the oscillation becomes intermittent. Additional problems
~21~i8~:~7
to solve the problem will be further described in detail.
The indirect control of the output voltage Vo by
controlling the base current iB by controlling the Zener
current iz by the equation (6) if the input voltage Vin is
raised or the load 15 is lightened to cause the Zener
current iz to increase was described above. However, since
the term of -(rz+rcf) increases as the Zener current iz
increases in term of the equation (7), the Zener voltage Vz
does not satisfy the equation (9) and the Zener diode ll
becomes the state that does not become on. Thus, the base
current iB becomes extreme~y larger than the target value
to cause the excessive current to flow, so that the on
period of the transistor 4 becomes extremely longer than
the target value, with the result that the output voltage
Vo largely increases. Therefore, since the Vf increases,
the Vcf also increases, the Vcf resultantly decreases, the
state that the base current iB does not flow is continued
until the Vz of the equation (7) satisfies the equation
(9), the oscillation of the transistor 4 becomes
intermittent to cause the transistor 4 to intermittently
oscillate. The stability of the output voltage Vo is
largely lost due to the intermittent oscillation.
If the environmental temperature varies, the values of
rcfr rz and iB alters, and the intermittent oscillation
tends to feasibly occur.
~ ~6132~
.
Further, the capacity Cf of the capacitor 10 increased
to ignore the influence in the equation (4) must be increased in
the actual circuit to cause the space and the cost of the R.C.C.
to become disadvantageous.
S
This invention has been made to eliminate the above-
described drawbacks of the prior-art R.C.C. and provides an
R.C.C. which largely widens varying ranges to load, input voltage
and temperature that the oscillation of the transistor 4 becomes
intermittent and the output voltage becomes unstable to improve
the characteristics and which does not need to apply a dummy load
nor to increase the value of the output capacitor 14.
In the R.C.C. of this invention, a first current out-
putted from a feedback winding of a transformer is branched to asecond current flowing to a branch circuit for varying an
impedance in response directly or indirectly to the voltage of a
primary winding, the feedback winding or a secondary winding when
a transistor is off, the base of the transistor is controlled by
the remaining current to control an output voltage, and an
impedance element is inserted through the base and emitter ~unc-
tion of the transistor in parallel with the branch circuit.
The R.C.C. of the invention inserts the impedance ele-
ment in series with the base and the emitter junction to therebyincrease the varying ranges to the load, the input voltage and
the temperature for turning on a Zener diode to act to remarkably
increase the varying range which does not cause the oscillation
to become intermittent.
Thus, according to one aspect of the present invention
there is provided a ringing choke-type DC/DC converter comprising
a transformer having primary winding, a feedback winding, a
secondary winding; a transistor having a base and an emitter and
connected between said primary winding and said feedback winding;
an input DC power source connected to said primary winding
-- 10 --
through said transistor; a DC power output connected to said
secondary winding; a base circuit having a first capacitor and
connected between the base of said transistor and said feedback
winding; a branch circuit branching from said base circuit and
having a Zener diode connected in series with a second capacitor,
and stabilizing means including an impedance element connected in
series between said transistor and said branch circuit for
Ereventing said transistor intermittently operating, thereby
stabilizing said DC power output. Suitably said second capacitor
of said branch circuit has a frequency-response impedance value
at a low temperature several times higher than that at an ambient
temperature. Desirably the Zener diode of said branch circuit
provides a voltage several times higher than a voltage variation
of said DC power output.
In another aspect of the present invention there is
provided a ringing choke-type DC/DC converter comprising a trans-
former having a primary winding, a feedback winding, and a sec-
ondary wind~ng; a transistor having a base and an emitter and
connected between said primary winding and said feedback winding;
an inpu~ DC power source connected to said primary winding
through said transistor; a DC power output connected to said sec-
ondary winding; a base circuit having a first capacitor and con-
nected between the case of said transistor and said feedback
winding; a branch circuit branching from said base circuit and
having a Zener diode connected in series with a second capacitor,
and stabilizing means including a constant voltage element con-
nected across the base and emitter of said transistor for pre-
venting said transistor from intermittently operating, thereby
stabilizing said DC power output.
In another aspect of the present invention there is
provided a ringing choke-type DC/DC converter comprising a trans-
former having a primary winding, a feedback winding, and a sec-
ondary winding; a transistor having a base and an emitter andconnected between said primary winding and said feedback winding;
-- 11 --
an input DC power source connected to said primary winding
through said transistor; a DC power output connected to said sec-
ondary winding; a base circuit having a first capacitor and con-
nected between the base of said transistor and said feedback
winding; a branch circuit branching from said base circuit and
having a zener diode connec-ted in series with a second capacitor,
and stabilizing means including a constant voltage element in
parallel with the branch circuit for preventing said transistor
from intermittently operating, thereby stabilizing said DC power
1 o output .
- lla -
~6~ 7
Now, an e~lbodiment of the present invention will be
described with reference to the accompanying drawings.
In Fig. 4, numeral 1 denotes a d.c. power source,
numeral 2 denotes a transformer, the starting end of a
primary winding 3 of the transformer 2 is connected to the
positive electrode of the d.c. pow~er source 2, and the
finishing end of the primary windi:ng 3 is connected to the
collector of a transistor 4. The ~emitter of the transistor
4 is connected to the negative electrode of the d.c. power
source 1. Numeral 5 denotes a starting resistor connected
at one end thereof to the positive electrode of the d.c.
power source 1, and connected at the other end thereof
through a resistor 16 to the base of the transistor 4.
Numeral 6 denotes a feedback winding of the transformer 2,
the starting end of the feedback winding 6 is connected
through a series circuit of a resistor 7, a capacitor 8 and
the resistor 16 to the base of the transistor 4, and the
finishing end of the feedback winding 6 is connected to the
emitter of the transistor 4. Numeral 9 denotes a diode,
the cathode side of the diode 9 is connected to the
starting end of the feedback winding 6, and the anode side
of the winding 6 is connected to the negative electrode of
a capacitor 10. The positive electrode of the capacitor 10
is connected to the finishing end of the feedback winding
6. Numeral 11 denotes a Zener diode, the cathode side of
- 12 -
i82~7
the diode 11 is connected to the connecting point a of the
resistor 5, the resistor 16 and the capacitor 8, and the
anode side of the diode 11 is connected to the negative
electrode of the capacitor 10. Numeral 12 denotes a
secondary winding of the transformer 2, the starting end of
the secondary winding 12 is connected to the negative
electrode of a capacitor 14, and the finishing end of the
secondary widing 12 is connected to the anode side of a
diode 13.- The cathode side of the diode 13 is connected to
the positive electrode of the capacitor 14. Numeral 15
denotes a load, which is connected to b~th ends of the
capacitor 14.
Since the operation of the R.C.C. constructed as
described above to its oscillation is the same as that of
the prior-art example shown in Fig. 1, the description
thereof will be omitted, and a voltage control of the
portion deeply related to an intermittent oscillation will
be described in detail.
When an equivalent circuit of the voltage controller
of Fig. 4 is drawn, Fig. 5 is attained. When an equation
corresponding to the equation (4) is calculated in the same
manner as the prior-art example from Fig. 5, the following
equation (10) is attained.
1 ~
(r +RBl)iB+vB=rziz+vz+ - )izdt VCf Cf z
- 13 -
~6~ 7
When the same assumption as that of the prior-art
example is preparedr the equation (10) can be represented
by the following equation (11).
VZ=RsliB+v~+vcf (rz Cf) Z (11)
Therefore, since the term of ~ 1xiB increases by inserting
the resistor 16 to the base and the emitter junction of the
transistor 4 even if an input voltage Vin rises or the load
15 increases to cause the Zener current iz to increase, the
off range of the Zener diode ll is widened, and even if the
Zener current iz increases in the amount of RB1xiB as
compared wi-th the equation (7) of the prior-art example,
the equation (9) is satisfied. Therefore, the ranges to
the load and the input voltage that does not cause the
oscillation to become intermittent are remarkably improved.
Since the term of RB1xiB is provided in the equation, the
range to the environmental temperature is also remarkably
improved.
In the embodiment described above, the resistor 16 has
been inserted between the base of the transistor 4 and the
connecting point a. However, the same advantages can be
also provided even if the resistor 16 is inserted between
the emitter side of the transistor 4 and a connecting point
b as shown, for example, in Fig. 6.
In the embodiment described above, the resistor 16 has
been used as a circuit element for generating a voltage
- 14 -
when the current flows. However, the same advantages can
be also provided even if the junction of a diode, a Zener
diode or a transistor, or the combination thereof is, for
example, inserted so that the direction for generating a
voltage is forward to the direction of the junction between
the base and the emitter of the transistor 4, and a reverse
current bypassing diode is connected directly or
indirectly.
In the embodiment described above, the base current of
the transistor 4 for controlling the output voltage has
been controlled by the Zener diode 11. However, any
circuit of circuit elements or its combination may be used
if the circuit can vary the impedance in response directly
or indirectly to the voltage of the primary winding 3, the
feedback winding 6 and the secondary winding 12 when the
transistor is off, and its example will be, for example,
shown in Fig. 7.
In the embodiment described above, the Zener diode 11
and the capacitor 11 are connected merely in series.
~owever, the same advantages can be also provided if the
present invention is applied to a circuit if the circuit is
provided to shorten the oscillation stopping period of the
intermittent oscillation by connecting the capacitor 10 and
a resistor in parallel.
According to the present invention as described above,
the impedance element is inserted in series with the base
and the emitter junction of the transistor for controlling
the output voltage of the R.C.C. Therefore, the allowable
varying ranges to the load, the input voltage and the
temperature which do not cause the oscillation to become
intermittent can be largely widened, thereby improving the
control characteristic, decreasing the capacity of the
capacitor which was increased heretofore to eliminate an
lntermittent oscillation and improving the space and the
cost. Since the dummy load heretofore mounted to eliminate
the intermittent oscillation can be obviated, the space,
the cost and the heat generation can be improved. Further,
the output capacitor can be set to the optimum capacity to
similarly improve the space, the cost and the heat.
The temperature characteristic of the capacitor 10
will be described. Fig. 8 shows frequency-impedance
characteristic of the capacitor 10 of the R.C.C. In Fig.
8, a solid line illustrates the impedance at the
environmental temperature tambient temperature) of 20C,
and a broken line illustrates the impedance at the
environmental temperature (low temperature) of -20C.
Since the R.C.C. is usually used in a frequency range of 10
to 100 kHz, it is understood from Fig. 8 that the impedance
v~riations at the ambient temperature becomes approx. 10
times as high as those at the low temperature. Since the
~6~0~
rcf increases at the low temperature in term of the
equation (7), the Zener voltage Vz does not satisfy the
equation (9~ according to the load and/or input voltage
conditions to become the state that the diode 11 is not
turned on. Thus, since the base current iB becomes
extremely larger than the target value to cause an
excessive current to flow to the transistor 4, the on
period of the transistor 4 becomes extremely longer than
the target value to cause the output voltage Vo to largely
increase. Therefore, since the feedback voltage Vf
increases, the charging voltage Vcf also increases, the
charging voltage Vcf resultantly decreases, the state that
the base current iB does not flow continues until the Zener
voltage Vz of the equation (7) again satisfies the equation
t9~, and the oscillation of the transistor 4 becomes
intermittent to cause the transistor 4 to become
intermittent. The stability of the output voltage Vo is
largely lost due to the intermittent oscillation.
Therefore, the capacitor 10 has characteristics that
the value of the capacity thereof in the switching
frequency of the transistor 4 becomes several times as
small as the value at the ambient temperature, i.e., the
characteristics as shown in Fig. 9. Thus, the variations
in the impedances at both the ambient and low temperatures
become several times or less. Therefore, since the
- - 17 -
variation in the impedance rcf is small, the influence o~
the term of the rcf in the equation (7) decreases to
satisfy the equation (9) at the low temperature, and the
temperature of the intermittent oscillation becomes
remarkably lower than that of the prior-art example,
thereby improving the usable temperature range.
Then, the Zener diode ll of the R.C.C. will be
described. The fact that, if the input voltage Vin is now
raised or the load 15 is lightened to cause the Zener
voltage iz to increase, the Zener current iz is controlled,
the base current iB is controlled and the output voltage Vo
is indirectly controlled according to the equation (6) is
as described above. Since the Zener diode 11 is heretofore
decided according to the allowable loss, the Zener diode
having the allowable loss as high as the loss usually
generated by observing the margin was used. Thus, since
the operating resistor Rz in the equation (7) affects
larger influence than the other terms and the term of
-(rz+rcf)iz increases as the Zener current iz increases,
the Zener voltage Vz does not satisfy the equation (9) so
that the Zener diode ll becomes the state that does not
become on. Therefore, since the base current iB becomes
extremely larger than the target value to cause the large
current to flow, the on period of the transistor becomes
extremely longer than the target value, thereby largely
- 18 -
~2~ 7
increasing the output voltage Vo. Accordingly, since the
feedback voltage Vf increases, the charging voltage Vcf
increases, the charging voltage Vcf resultantly decreases,
the state that the base current iB does not flow until the
Zener voltage Vz of the equation (7) again satisfies the
equation (9) continues so that the oscillation of the
transistor 4 becomes intermittent to cause the transistor
to become intermittent. The stability of the output
voltage Vo is largely lost due to the intermittent
oscillation.
If the environmental temperature varies, the impedance
component rcf of the capacitor 10, the operating resistance
rz of the Zener diode 11 and the operating resistance rB f
the transistor vary, and it becomes the state that the
intermittent oscillation feasibly occurs.
The capacitor Cf of the capacitor 10 which is
increased to ignore the influence in the equation (4) must
be increased in the actual circuit so that the space and
the cost become disadvantageous. Therefore, the Zener
diode 11 has the allowable loss several times as high as
the loss generated therein. Thus, the operating resistance
of the Zener diode is lower than the prior-art example, and
the influence of the voltage drop due to the Zener current
flowing to the branch circuit when the base current flows
can be suppressed to low, thereby largely widening the
- 19 -
~6~ 7
varying ranges to the load, the input voltage and the
temperature which causes the oscillation to become
intermittent to improve the characteristics.
Then, the voltage VcE between the collector and the
emitter of the transistor 4 will be described. A reverse
voltage is generated, as shown in Fig. 1, between the base
and the emitter of the transistor 4 when the transistor 4
is turned off, but the voltage of the feedback winding 6
moves in the direction for eliminating the voltage when the
variation in the magnetic flux in the core of the
transformer 2 becomes constant as described with respect to
Fig. 1. Thus, the voltage of the feedback winding 6
decreases, and the voltage VBE between the base and the
emitter of the transistor 4 becomes positive. Therefore,
the transistor 4 tends to turn on at this time, but since
the base current iB is less, the transistor 4 cannot be
sufficiently saturated. Thus, the VcE waveform is deformed
as shown by a broken line in Fig. 2. Since the collector
current ic also flows to the transistor 4, a loss is
generated to cause the transistor 4 to be largely heated.
Therefore, it becomes necessary to increase a cooling fin
or to select the transistor 4 of large margin, thereby
increasing the cost. Thus, as shown in Fig. 10, a
constant-voltage element of a constant-voltage diode 19 is
connected to the transistor 4. In other words, the
- 20 -
constant-voltage diode 19 is connected at the cathode side
thereof to the emitter of the transistor 4, and connected
at the anode side thereof to the base of the transistor 4.
In the R.C.C. constructed as descrlbed above, the
operation to the oscillation is the same as that of the
prior-art example shown in Fig. l, and the description
thereof wi].l be accordingly omitted. The elimination of
the distortion of the waveform of the collector voltage VcE
will be described in detail. A voltage of deeply negative
direction is applied between the base and the emitter of
the transistor 4 by the operation of the constant-voltage
diode 19 in term of the off period of the transistor 4.
Therefore, when the variation in the magnetic flux in the
core of the transformer 2 becomes constant, the feedback
winding voltage starts decreasing, but since the base and
the emitter voltage does not become positive until the base
current iB becomes the sufficient value for saturating the
transistor 4, the transistor 4 is not turned on, thereby
eliminating the distortion of the VcE waveform like the
prior-art example to obviate the loss due to the
distortion.
In the embodiment described with respect to Fig. 10,
the constant-voltage diode 19 has been connected between
the base and the emitter of the transistor 4 to deepen the
voltage between the base and the emitter to the negative
~6~
side in the state that the transistor 4 was off. However~
the constant-voltage diode 19 may be any if it is
constant-voltage element, and the constant-voltage diode 19
may be connected in series with a diode 20 as shown in Fig.
11 .
- 22 -
