JPH0247197B2 - JIREIHATSUSHINKI - Google Patents

Description

Detailed Description of the Invention Technical Field The present invention relates to a self-excited oscillator for a DC-DC converter, etc., called an on-off type stone-type transistor converter or a ringing chain-type transistor converter, and more particularly, to a self-excited oscillator for a DC-DC converter, etc., which has low power loss. This invention relates to an excited transistor oscillation circuit.

Conventional technology On-off type DC-DC including conventional self-excited oscillation circuit
In Figure 1 showing the converter, 1 is a DC power supply, 2
3 is an output transformer, and 3 is a switching transistor, which are connected in series. That is, one end of the primary winding 4 of the transformer 2 is connected to one end (positive terminal) of the DC power supply 1, the other end is connected to the collector of the switching transistor 3, and the emitter of the switching transistor 3 is connected to the other end of the DC power supply 1. connected to the terminal (negative terminal). transformer 2 is 2
In addition to the secondary winding 5, it also has a tertiary winding 6, and a secondary winding 5
A rectifying and smoothing circuit 9 consisting of a rectifying diode 7 and a capacitor 8 is connected to the output stage, and a load 1 is connected to the output stage.
0 is connected. The tertiary winding 6 is a base drive winding, and one end (upper end) of the tertiary winding 6 is a current limiting resistor 11.
The other end (lower end) is connected to the emitter. A starting resistor 15 is connected between one end of the power supply 1 and the base of the switching transistor 3. Reference numeral 16 denotes a voltage control transistor, which is connected between the base and emitter of the switching transistor 3. 17 is a voltage control circuit, which compares the voltage detected from the output line of the rectifying and smoothing circuit 9 with the reference voltage of the reference power supply 18, and includes a differential amplifier 19 that outputs an output voltage corresponding to the difference between the two; It includes a light emitting element 20 that is in a light emitting state according to the output of the dynamic amplifier 19, and a control element 21 that is a light receiving element whose impedance changes in response to the light emission of the light emitting element 20. In addition,
The output voltage control element 21 is connected between the base of the voltage control transistor 16 and ground.

Next, the operation of the circuit shown in FIG. 1 will be explained. First, when the power supply 1 of the converter is turned on, the base current of the switching transistor 3 flows through the starting resistor 15, turning on the transistor 3 and starting oscillation. During the ON period of the switching transistor 3, the power supply voltage is applied to the primary winding 4, and a voltage is also obtained in the tertiary winding 6 accordingly, causing the base current to flow through the switching transistor 3.
I _B is supplied. As a result, the conduction of the transistor 3 is maintained, and the collector current I _C gradually increases. At this time, a voltage is generated in the secondary winding 5 that turns off the diode 7, and the release of energy is prevented. After that, when h _FE · I _B (where h _FE is the current amplification factor of transistor 3) is reached and transistor 3 is saturated, it becomes impossible to increase the collector current I _C and transistor 3 goes into an unsaturated state. do.
As a result, the voltage across the primary winding 4 decreases, the base current also decreases, and the transistor 3 suddenly turns off. The energy stored in the transformer 2 while the transistor 3 is on is released through the rectifier diode 7 while the transistor 3 is off. While the transformer 2 is discharging energy, a voltage is generated in the tertiary winding 6 that reverse biases the transistor 3, so the transistor 3 does not turn on, but when the energy dissipation ends,
The transistor 3 is turned on again due to ringing caused by the leakage inductance of the transformer 2.

In the above-mentioned oscillation state, for example, when the output voltage becomes higher than the reference voltage, the differential amplifier 19
The output of the light emitting element 20 increases, and the intensity of light emitted from the light emitting element 20 also increases. As a result, the resistance value of the output voltage control element 21 decreases, the base current of the voltage control transistor 16 increases, and the voltage control transistor 16
Bypass current flowing to increases. Therefore, the base current I _B of the switching transistor 3 decreases, the peak of the collector current I _C of the switching transistor 3 determined by h _FE · I _B is also suppressed low, and the energy stored in the transformer 2 becomes small.
The output voltage V ₀ is returned to the reference voltage. Output voltage V ₀
When is lower than the reference value, the operation is opposite to the above.

By the way, in order to increase the capacity of this converter, it is necessary to increase the peak value of the collector current of the switching transistor 3, which inevitably requires a large base current _IB . Losses due to resistance increase. or,
As the input voltage increases, the base current also increases in proportion to this, leading to overdrive, increasing switching loss in the switching transistor 3, and reducing efficiency. Furthermore, since the voltage control transistor 16 controls the base current I _B of the switching transistor 3 in class-A operation, the power loss in the voltage control transistor 16 becomes large and the efficiency decreases.

OBJECT OF THE INVENTION Therefore, an object of the present invention is to provide a self-excited oscillator with low power loss.

Structure of the Invention To achieve the above object, the present invention will be described with reference to the reference numerals in the drawings showing the embodiments for ease of understanding. a switching transistor 3 connected in series with the transformer 4; a DC power supply 1 that supplies a DC voltage to a series circuit consisting of the primary winding 4 and the switching transistor 3; and the primary winding of the transformer 2. a secondary winding 5 electromagnetically coupled to the transformer 2; a starting circuit connected to the base of the switching transistor 3; and the primary winding 4 of the transformer 2.
and a tertiary winding 6 electromagnetically coupled to the secondary winding 5.
and a base drive circuit connected to the base of the switching transistor 3 so as to supply a base current based on the induced voltage of the tertiary winding 6;
A current corresponding to the current in the primary winding 23 of the current transformer 22 connected in series to the emitter or collector of the current transformer 22 and the current in the primary winding 23 of the current transformer 22 is supplied to the base of the switching transistor 3. The secondary winding 2 of the current transformer 22 is connected between the base and emitter of the switching transistor 3 as shown in FIG.
4, a control transistor 16 connected directly or indirectly between the base and emitter of the switching transistor 3, and a control transistor 16 for controlling the output voltage obtained at the output stage of the secondary winding 5 of the transformer 2. For example, a control circuit including the control element 21 of the embodiment and the switching transistor 3
generates a gradient voltage in one direction in synchronization with turning on of the switching transistor 3, and the slope of the gradient voltage is controlled by the control circuit;
a triangular wave voltage generating circuit 27 that generates a ramp voltage in the opposite direction to the one direction in synchronization with the turning off of the triangular waveform voltage generating circuit 27;
The present invention relates to a self-excited oscillator comprising a circuit including, for example, the transistor 33 of the embodiment, which detects that the gradient voltage in one direction has reached a predetermined level and turns on the control transistor 16.

Effects of invention According to the above invention, the following effects can be obtained.

(a) Since the base of the switching transistor 3 is controlled by current feedback from the current transformer 22 and also by voltage feedback from the tertiary winding 6 of the transformer 2, a highly efficient self-excited oscillator can be provided. .

(b) Since the collector current or emitter current of the switching transistor 3 is fed back to the base by the current transformer 22, the base current increases as the collector current or emitter current increases. Therefore, it is no longer necessary to constantly flow the base current required to obtain the desired peak value of the collector current, and efficiency is improved.

(c) Since the base current based on the tertiary winding 6 of the transformer 2 decreases, even if the voltage of the tertiary winding 6 increases due to an increase in input voltage, the base current of the switching transistor 3 will decrease significantly. Does not increase. Therefore, increase in switching loss due to overdrive can be reduced.

(d) Since the voltage control transistor 16 performs a switching operation to control the on-time of the switching transistor 3, the voltage control transistor 1
6 is reduced.

(e) As described above, the power loss in each part of the switching transistor 3 and its control circuit is significantly reduced, so the efficiency of the oscillator is improved.

Embodiment Next, a DC-DC converter including a self-excited oscillator according to an embodiment of the present invention will be described with reference to FIGS. 2 and 3. However, in Figure 2, the code 1
21 are substantially the same as those indicated by the same reference numerals in FIG. 1, so their explanation will be omitted.

In the DC-DC converter shown in FIG. 2, the primary winding 23 of a single-turn current transformer 22 is connected in series with the emitter of the switching transistor 3.
The secondary winding 24 of the current transformer 22 is connected to the switching transistor 3 via a rectifier diode 25 for blocking reverse current.
It is connected between the base and emitter of. In addition,
The turns ratio of current transformer 22 is set to 1:h _FE .

26 is a capacitor as a trigger circuit;
One end of the tertiary winding 6 and the switching transistor 3
is connected in series with the base of Because this capacitor 26 is provided, even if voltage continues to be generated in the tertiary winding 6 during the ON period of the switching transistor 3, the base current is not continuously supplied from the tertiary winding 6, and the switch Only the on trigger signal of the switching transistor 3 is supplied.

27 is a triangular wave voltage generating circuit, which includes a quaternary winding 28 of the transformer 2 and a triangular wave generating capacitor 29.
and two backflow blocking diodes 30 and 31,
It consists of a resistor 32 for discharge time constant. One end of the triangular wave generating capacitor 29 is connected to one end of the quaternary winding 28, and the other end is connected to the other end of the quaternary winding 28 via a backflow blocking diode 30 and an output voltage control element 21. There is. Note that the polarity of the quaternary winding 28 is set so that the reverse current blocking diode 30 is turned on during the on period of the switching transistor 3. The reverse current blocking diode 31 and the discharging resistor 32 are connected to the other end of the capacitor 29 and the quaternary winding 2.
8 and the other end. Note that the diode 31 is turned on during the off period of the switching transistor 3.

33 is a transistor for turning on the transistor 16, its emitter is connected to one end of the capacitor 29, its base is connected to the other end of the capacitor 29, and its collector is connected to the resistor 34.
It is connected to the base of the off-control transistor 16 via. The collector of the OFF control transistor 16 is connected to the base of the switching transistor 3 via a current limiting resistor 34, and its emitter is connected to the emitter of the switching transistor 3 via an auxiliary power supply capacitor 35.
Note that the capacitor 35 is connected in parallel to the quaternary winding 28 via a diode 36, and is charged during the ON period of the switching transistor 3.

Next, the operation of the circuit shown in FIG. 2 will be explained with reference to the waveform diagram shown in FIG. When the DC power supply 1 is connected, the switching transistor 3 is connected through the starting resistor 15.
Base current flows and oscillation begins. After that,
At time t ₁ in FIG. 3, if a voltage that turns on the switching transistor 3 is generated in the tertiary winding 6, a differential current I _B1 shown in FIG. 3 flows through the capacitor 26 to the base of the switching transistor 3. The switching transistor 3 turns on quickly and reliably. When the switching transistor 3 is turned on, a collector current I _C flows, which gradually increases as shown in FIG. As a result,
A current I _B2 is supplied to the switching transistor 3 through current feedback by the current transformer 22 . Therefore, the combined current I _B of I _B1 and I _B2 flows through the switching transistor 3. On the other hand, during the ON period of the switching transistor 3, the following operation occurs in the triangular wave voltage generation circuit 27. When the switching transistor 3 is turned on at _t1 in FIG. 3, a voltage is generated in the quaternary winding 28 to charge the capacitor 29, and charging of the capacitor 29 starts. Note that this charging current flows through the diode 30 and the control element 21. Therefore, the charging time constant is determined by C of the capacitor 29 and the resistance R of the control element 21 consisting of the diode 30 and the phototransistor. Since the resistance value of the control element 21 changes so that it becomes small when the output voltage is large and becomes large when the output voltage is small, the charging time constant CR changes depending on the output voltage. As the capacitor 29 is charged, the potential V _A at the lower end of the capacitor 29 gradually decreases from t ₁ to t ₂ as shown in FIG. When the potential V _A reaches the base-emitter voltage -V _BE at which the transistor 33 is turned on, the transistor 33 is turned on and the potential flows into the base of the on-control transistor 16 in the next stage. As a result, a bypass circuit for the base current _IB of the switching transistor 3 is formed, and the base current decreases, and a reverse bias is applied to the switching transistor 3 via the capacitor 35, so that the switching transistor 3
is turned off. As a result, an opposite voltage is obtained in the tertiary winding 6, and this voltage and the voltage of the capacitor 26 reverse bias the switching transistor 3. After that, the remaining charge of the capacitor 26 is transferred to the resistor 11. , tertiary winding 6, current transformer secondary winding 2
4. Emitted by a circuit consisting of a diode 25.

On the other hand, in the triangular wave voltage generation circuit 27, the capacitor 29 is discharged during the off period of the switching transistor 3. That is, the quaternary winding 28
The diode 31 is turned on by the voltage generated during the off period, and the charge in the capacitor 29 is discharged in a discharge circuit consisting of the capacitor 29, the quaternary winding 28, the resistor 32, and the diode 31. Note that the time constant of this discharge circuit is constant regardless of the output voltage.

During this off period, when the energy release from the transformer 2 is completed, a voltage is generated again to turn on the switching transistor 3, the transistor 3 is turned on, and charging of the triangular wave generating capacitor 29 is started.

Next, voltage control will be described. Now, if the output voltage becomes low, the resistance value of the control element 21 becomes large, and the charging time constant of the capacitor 29 becomes large. As a result, the time it takes for the potential V _A to reach -V _BE becomes longer as shown by the dotted line in FIG. 3, and the on period of the switching transistor 3 also becomes longer. Therefore, the output voltage is returned to the original voltage. Contrary to the above, when the output voltage increases, the operation is opposite to the above. In addition, in order to control the output voltage, the collector current of the switching transistor 3 is
The charging time constant of the capacitor 29 is determined so that the transistor 16 is turned on before I _C reaches h _FE · I _B .

As is clear from the above, in this circuit, it is not necessary to always supply a constant base current from the tertiary winding 6 that can obtain the peak value of the collector current I _C , and the trigger current that turns on the transistor 3 is Just let it flow. Therefore, power loss caused by the resistor 11 and the like is reduced.

Furthermore, since the base current I _B of the switching transistor 3 is supplied by current feedback from the current transformer 22, the base current I _B is not constant as shown in FIG. Therefore, the base current required to obtain the peak value of the collector current I _C does not flow during periods other than the peak value, and power loss during the on period is reduced. Note that only the diode 25 is inserted between the current transformer 22 and the base of the transistor 3, and the power loss here is small.

Furthermore, since the transistor 16 for voltage control and off control is turned on only during off control, the power loss in the circuit of the resistor 34 and this transistor 16 is extremely small.

Modifications The present invention is not limited to the embodiments described above, and, for example, the following modifications are possible.

(a) The current transformer 22 may be connected to the collector side of the switching transistor 3.

(b) Instead of using a phototransistor as the control element 21, it may be another light receiving element, a bipolar transistor, or an FET.

(c) It can also be applied to open-loop voltage control without feedback control. In this case, the control element 21 may be a variable resistor.

(d) The circuit configuration of the triangular wave voltage generation circuit 27 may be modified to various circuits that generate a triangular wave in synchronization with turning on of the switching transistor 3.

(e) A low level constant current may be supplied from the tertiary winding 6 during the on period without providing the capacitor 26.

(f) The starting resistor 16 may be connected to a power source or signal source different from the power source 1.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a conventional DC-DC converter, Fig. 2 is a circuit diagram showing a DC-DC converter according to an embodiment of the present invention, and Fig. 3 shows the state of each part in Fig. 2. FIG. 1...DC power supply, 2...Transformer, 3...Switching transistor, 4...Primary winding, 5...
Secondary winding, 6... Tertiary winding, 8... Rectifier and smoothing circuit, 11... Resistor, 15... Starting resistance, 16...
Voltage control transistor, 17... Voltage control circuit, 21... Output voltage control element, 22... Current transformer, 23... Primary winding, 24... Secondary winding, 25
...Diode, 26...Trigger capacitor,
27...triangular wave voltage generation circuit, 28...quaternary winding, 29...triangular wave generation capacitor, 33...detection control transistor.

Claims (1)

[Claims] 1. A transformer comprising: a primary winding 4 of a transformer 2; a switching transistor 3 connected in series to the primary winding 4; and the primary winding 4 and the switching transistor 3. a DC power supply 1 that supplies DC voltage to a series circuit; a secondary winding 5 electromagnetically coupled to the primary winding 4 of the transformer 2; and a starting circuit connected to the base of the switching transistor 3. It includes a tertiary winding 6 that is electromagnetically coupled to the primary winding 4 and the secondary winding 5 of the transformer 2, and is configured to supply a base current based on the induced voltage of the tertiary winding 6. a base drive circuit connected to the base of the switching transistor 3; a primary winding 23 of the current transformer 22 connected in series to the emitter or collector of the switching transistor 3; a secondary winding of the current transformer 22 connected between the base and emitter of the switching transistor 3 so as to supply a current corresponding to the current of the primary winding 23 to the base of the switching transistor 3; 24; a control transistor 16 connected directly or indirectly between the base and emitter of the switching transistor 3; and a control transistor 16 for controlling the output voltage obtained at the output stage of the secondary winding 5 of the transformer 2. a control circuit for generating a ramp voltage in one direction in synchronization with turning on of the switching transistor 3, and the slope of the ramp voltage being controlled by the control circuit;
a triangular wave voltage generation circuit 27 that generates a ramp voltage in the opposite direction to the one direction in synchronization with the turning off of the switching transistor 3; , and a circuit for turning on the control transistor 16. 2 The base drive circuit is connected to 3 of the transformer 2.
The self-excited oscillator according to claim 1, which is a circuit including a capacitor (26) for supplying a differential current to the base of the switching transistor (3) based on the output of the next winding (6). 3. The triangular wave voltage generating circuit 27 is configured to be charged by the voltage generated in the quaternary winding 28 provided in the transformer 2 and the quaternary winding 28 during the ON period of the switching transistor 3. and a discharge circuit that controls the capacitor 29 to a discharge state in response to the voltage generated in the quaternary winding 28 during the off period of the switching transistor 3. The self-excited oscillator according to the range 1 or 2. 4 The circuit for controlling the control transistor 16 to turn on has an emitter connected to one end of the capacitor 29, a base connected to the other end of the capacitor 29, and a collector connected to the control transistor 16.
4. A self-excited oscillator according to claim 3, which is a circuit including a transistor 33 connected to the base of the self-exciting oscillator.