JPH0231592B2 - CHOKURYUUCHOKURYUHENKANKI - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a transistor DC-DC converter capable of reducing power loss.

Prior Art In Fig. 1 showing a conventional self-excited on-off transistor DC-DC converter, 1 is a DC power supply;
2 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 overcurrent detection resistor R. ₁ to the other end (negative terminal) of the DC power supply 1. In addition to the secondary winding 5, the transformer 2 has
It also has a tertiary winding 6, a rectifying and smoothing circuit 8 consisting of a rectifying diode 7 and a capacitor 9 is connected to the secondary winding 5, and a load 10 is connected to this output stage. The tertiary winding 6 is a base drive winding, and one end (upper end) thereof is connected to the base of the switching transistor 3 via a current limiting resistor 11, and the other end (lower end) is connected to the emitter. 15 is a constant voltage control circuit, which includes a constant voltage control capacitor 12 and a rectifier diode 13 for capacitor charging.
and a Zener diode 14 as a constant voltage diode. One end of a capacitor 12 in this constant voltage control circuit 15 is connected to the lower end of the tertiary winding 6, and the other end is connected to the upper end of the tertiary winding 6 via a rectifier diode 13. Since the rectifier diode 13 has a directionality that makes it conductive in response to the induced voltage of the tertiary winding 6 that reverse biases the transistor 3, the capacitor 12 has a directionality that makes it conductive in response to the induced voltage of the tertiary winding 6 that reverse biases the transistor 3. The voltage of the line 6, ie, the regulated voltage, is charged. A Zener diode 14 as a constant voltage diode is connected between the other end of the capacitor 12 and the base of the transistor 3. The Zener diode 14 is connected in such a direction that it breaks down to a constant voltage when the transistor 3 is forward biased. Reference numeral 16 denotes a starting resistor, which is connected between the base of the switching transistor 3 and the DC power supply 1. The collector of the overcurrent control transistor Q is connected to the base of the switching transistor 3, its emitter is connected to the lower end of resistor _R1 , and its base is connected to the upper end of resistor _{R1 via resistor R2 .}

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 16, turning on the transistor 3 and starting oscillation. During the ON period of the switching transistor 3, a power supply voltage is applied to the primary winding 4, and a voltage is also obtained in the tertiary winding 6 in response to this, and as shown in FIG. Base current I _B is supplied to transistor 3 . As a result, the conduction of the transistor 3 is maintained, and the collector current I _C gradually increases as shown in FIG. 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, h _FE・I _B (however, h _FE is transistor 3
When transistor 3 reaches saturation (current amplification factor), it becomes impossible to increase collector current I _C ,
Transistor 3 goes into an unsaturated state. As a result, the voltage across the primary winding 4 decreases, the base current also decreases, and the transistor 3 suddenly turns off.
Then, the period during which the transistor 3 is on (t ₁ to _{t 2} )
The energy stored in the transformer 2 is released through the rectifier diode 7 during the period when the transistor 3 is off (t ₂ to _{t 3} ). While the energy of the transformer 2 is being released, a voltage is generated in the tertiary winding 6 that reverse biases the transistor 3, so the transistor 3 does not turn on. However, once the energy is released, the leakage inductance of the transformer 2 The transistor 3 is turned on again due to the ringing caused by the above.

The capacitor 12 of the constant voltage control circuit 15 is charged with the voltage of the tertiary winding 6 during the off period of the transistor 3. Since the voltage of the tertiary winding 6 during this off period corresponds to the output voltage V ₀ , the capacitor 12 is charged with a voltage corresponding to fluctuations in the output voltage V ₀ . Note that the capacitor 12 is charged in a direction that reverse biases the transistor 3. A series circuit of a Zener diode 14 and a capacitor 12 is connected in parallel to the emitter-base junction of the transistor 3, and the Zener diode 14 has a directionality that breaks down at the voltage when the transistor 3 is turned on. The base bias of the transistor 3, that is, the base current, is controlled by the voltage difference between the constant voltage, that is, the reference voltage, obtained across the transistor 14, and the charging voltage of the capacitor 12, and a constant voltage characteristic is obtained. Now, if the output voltage becomes high, the capacitor 12 becomes the diode 13 during the off period.
charged to a high voltage via the As a result, when the base current is supplied to the transistor 3 using the voltage generated in the tertiary winding 6 during the ON period of the transistor 3, the current flowing through the Zener diode 14 increases and the base current flowing to the transistor 3 decreases. As a result, the peak of the collector current I _C determined by h _FE I _B is also suppressed to a low level, the energy stored in the transformer 2 is reduced, and the output voltage V ₀
is returned to the reference voltage. When the output voltage V ₀ is lower than the reference value, the operation is opposite to the above.

When the emitter current of transistor 3 exceeds a certain value due to a short circuit in load 10, etc., the overcurrent detection resistor
Transistor Q is turned on based on the voltage drop across _R1 , the base current _IB is shunted to this transistor Q, and the current of switching transistor 3 is limited.

By the way, this converter uses an overcurrent detection resistor.
Since _R1 is connected in series with the switching transistor 3, power loss here is large.
Furthermore, since a constant base current I _B is always supplied during the on period from t ₁ to _{t 2} regardless of the magnitude of the collector current I _C , loss increases.

OBJECT OF THE INVENTION Therefore, an object of the present invention is to provide a transistor DC-DC converter with low 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. 4, a rectifying and smoothing circuit 8 connected to the secondary winding 5, and a primary winding 18 of a current transformer 17 connected in series to the switching transistor 3. and the transformer connected between the base and emitter of the switching transistor 3 so as to supply a current corresponding to the current in the primary winding 18 of the current transformer 17 to the base of the switching transistor 3. An overcurrent detection resistor 22 connected in series with the secondary winding 19 of the current transformer 17 and the secondary winding 19 of the current transformer 17 is connected between the base and emitter of the switching transistor 3. an overcurrent control transistor 21,
One end of the overcurrent detection resistor 22 and the overcurrent are connected so that the overcurrent control transistor 21 is operated for overcurrent control in response to the voltage drop across the overcurrent detection resistor 22 exceeding a certain value. an overcurrent control current supply circuit connected between the base of the current control transistor 21 and a control signal supply circuit for supplying a control signal for controlling on/off of the switching transistor 3 to the base of the switching transistor 3; This relates to a DC-DC converter consisting of a circuit.

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

(a) Since the overcurrent detection resistor 22 is provided on the secondary side of the current transformer 17 for current feedback, and the overcurrent control transistor 21 is controlled based on this, the power in the overcurrent detection resistor 22 is Loss current transformer 17
can be reduced in accordance with the turns ratio.

(b) Since the current transformer 17 is shared for current feedback and overcurrent detection, the circuit configuration is simplified.

(c) Since the collector current or emitter current of the switching transistor 3 is fed back to the base by the current transformer 17, the base current increases as the collector current or emitter current increases. Therefore, it is no longer necessary to constantly return the base current required to obtain the desired peak value of the collector current, improving efficiency.

Embodiment Next, a DC-DC converter according to an embodiment of the present invention will be described with reference to FIGS. 3 to 11.
However, in Figures 3 to 11, the numbers 1 to 16
Components indicated by are substantially the same as those indicated by the same reference numerals in FIG. 1, so a description thereof will be omitted. In addition, the same reference numerals are given to parts that are common to each other in Figs. do.

First Embodiment In the DC-DC converter according to the first embodiment shown in FIG.
A primary winding 18 of a current transformer 17 is connected in series to the collector of the transistor 3, and a secondary winding 19 of the current transformer 17 is connected between the base and emitter of the switching transistor 3 via a rectifier diode 20 for blocking reverse current. has been done. Note that the turns ratio of the current transformer 17 is set to 1:h _FE . A resistor 11 connected between the tertiary winding 6 of the transformer 2 and the base of the transistor 3
is set so that the base current is significantly limited compared to the circuit shown in FIG. Reference numeral 21 denotes an overcurrent control transistor, which is connected between the base and emitter of the switching transistor 3. 22 is a resistor for overcurrent detection, and current transformer 17
is connected in series to the secondary winding 19 of. Reference numeral 23 denotes a comparison control transistor as an overcurrent control current supply circuit, whose emitter is connected to one end of the overcurrent detection resistor 22, and whose base is connected to the resistor 24.
The collector is connected to the other end of the overcurrent detection resistor 22 through the overcurrent control transistor 21.
connected to the base of.

Since the DC-DC converter constructed as shown in FIG. 3 has a starting resistor 16 and a tertiary winding 6 of the transformer 2, it starts in the same way as the converter shown in FIG.
Then, during the on period of transistor 3,
A composite current I _B of currents I _B1 and I _B2 shown in FIG. 4 becomes the base current of the transistor 3, and the collector current increases with a slope as shown by I _C in FIG. Note that I _B1 is a constant base current supplied from the tertiary winding 6 of the transformer 2 based on voltage feedback,
I _B2 is the base current supplied from the secondary winding 19 of the current transformer 17 based on current feedback, and the current I _B1
is set smaller than the maximum value of current I _B2 . When the output voltage increases, the charging voltage of the capacitor 12 increases as in the case of Fig. 1, the base current is shunted through the Zener diode 14, and the current I _B flowing into the base of the transistor 3 decreases. However, as in the case of FIG. 1, the output voltage decreases.

A triangular wave voltage is generated across the overcurrent detection resistor 22 in response to changes in the collector current I _C , and this is applied between the base and emitter of the comparison control transistor 23 via the resistor 24, resulting in a base-emitter voltage. Compared to V _BE . Overcurrent detection resistor 22
When the voltage across the voltage is low, the comparison control transistor 23 does not become conductive, so the overcurrent control transistor 21 is also kept off. On the other hand, load 10
If the collector current I _C increases due to a short circuit, etc., the voltage across the overcurrent detection resistor 22 is increased, the comparison control transistor 23 is turned on, and the voltage across the current transformer 17 is increased.
The current in the next winding 19 flows into the base of the overcurrent control transistor 21 via the transistor 23,
Transistor 21 is turned on. As a result, the base current supplied from the secondary winding 19 of the current transformer 17 and the tertiary winding 6 of the transformer 2 is transferred to the transistor 21.
The collector current I _C of the switching transistor 3 is limited.

According to the method shown in FIG. 3, there is no need to connect the overcurrent detection resistor 22 in series with the switching transistor 3, so the power loss due to the overcurrent detection resistor 22 is reduced compared to the conventional circuit shown in FIG. 1/
h _FE can be reduced.

Additionally, since the base current gradually increases due to the feedback of the collector current I _C , significant excess base current is limited from flowing before the collector current I _C reaches its peak, improving efficiency.

Further, a control signal supply circuit for controlling on/off of the switching transistor 3 is constituted by a tertiary winding 6 of the transformer 2, and based on this tertiary winding 6, a current is generated when the transistor 3 starts to be turned on.
Since I _B1 is supplied by voltage feedback, self-oscillation can be continued stably.

Also, as the input voltage increases, the current increases accordingly.
Even if I _B1 increases, since the ratio of I _B1 to the total base current I _B is small, the increase in switching loss due to overdrive is small.

Second Embodiment In the second embodiment of the converter shown in FIG.
In place of the transistor 23 in the figure, a Zener diode 25 is connected between one end of the resistor 22 and the base of the transistor 21;
A resistor 26 is placed between the base of and its emitter line.
is connected. When this converter enters the current state, the voltage drop across the overcurrent detection resistor 22 increases, the Zener diode 25 as an overcurrent control current supply circuit becomes conductive, and a large base current flows into the transistor 21, causing the resistance value As the current decreases, the base current of the switching transistor 3 becomes more shunted, and the switching transistor 3
The base current of I C decreases and the collector current I _C is limited. In the converter shown in FIG. 5, constant voltage control is not performed based on voltage detection at the tertiary winding 6 of the transformer 2, but based on voltage detection at the load 10. That is, an error amplifier 28 is provided that compares and amplifies the output voltage at one end of the load 10 and the reference voltage provided from the reference voltage source 27, and an output corresponding to the difference between the two inputs obtained from the error amplifier 28 is sent to the light emitting diode 29. is supplied to Since the phototransistor 30 is optically coupled to the light emitting diode 29, the phototransistor 30 is controlled in accordance with the output voltage. Now, if the output voltage increases, the error output increases, and the resistance of the phototransistor 30 connected between the secondary winding 19 of the current transformer 17 and the base of the transistor 21 decreases. , the base current of transistor 21 increases, the base current of switching transistor 3 decreases, and the output voltage decreases. Note that during normal operation, the Zener diode 25 is kept off,
Transistor 21 operates in a non-saturation region. Fifth
If configured as shown in the figure, the transistor 21 is used for both overcurrent control and constant voltage control, so
Configuration is simplified. Third Embodiment The converter of the third embodiment shown in FIG. 6 is configured to limit the current with a fold-back droop characteristic when the load is short-circuited. That is, the current detection resistor 22 is connected to the upper end of the secondary winding 19 of the current transformer 17 and the common line 3.
1, a resistor 32 is connected between the upper end of this resistor 22 and the base of the control transistor 21, and the control transistor 21 is of a PNP type.
The collectors of are connected to the common line 31.
Further, a quaternary winding 33 is provided to detect the output voltage with a polarity opposite to that of the tertiary winding 6.
A capacitor 35 is connected in parallel to the next winding 33 via a rectifier diode 34, and this capacitor 35
The lower end of the control transistor 21 is connected to the control transistor 21 via the resistor 36.
connected to the base of. When this converter enters an overcurrent state due to a short circuit and the output voltage decreases, the voltage of the capacitor 35 also decreases, and the resistor 36 and resistor 3
2 also decreases, the base current of the control transistor 21 increases, and conversely, the base current of the switching transistor 3 decreases, and the collector current also decreases. As a result, when the output voltage decreases, the base current of the control transistor 21 flows more easily, and the current-voltage characteristic becomes a fold-back drooping characteristic. Note that even when an overcurrent is detected by the resistor 22, the base current of the control transistor 21 increases, thereby limiting the overcurrent. In the embodiment shown in FIG. 6 as well, the control transistor 21 is used for both overcurrent control and constant voltage control. That is, the phototransistor 30 is connected between the lower end of the capacitor 12 charged with the voltage of the tertiary winding 6 of the transformer 2 and the base of the control transistor 21 . In this circuit, when the output voltage becomes higher than the reference voltage, the resistance of the phototransistor 30 decreases, the base current of the control transistor 21 increases, the base current of the switching transistor 3 decreases, and the output voltage decreases. do.

Fourth Embodiment A converter according to a fourth embodiment shown in FIG. 7 has a differentiating circuit consisting of a capacitor 38 and a resistor 39 connected in place of the current limiting resistor 11 of the converter shown in FIG.
Further, a diode 40 is connected between the base and emitter of the transistor 3 to form a discharge circuit for the capacitor 38. In this converter, the base current I _B2 of I _C /h _FE flows as shown in FIG. 8 due to current feedback by the current transformer 17, and the differential shown as I _B1 in FIG. 8 when the transistor 3 is on and off flows. A current flows through the capacitor 38, and the combined current of the currents I _B1 and I _B2 , indicated by I _B in FIG. 8, becomes the base current of the transistor 3. That is, when the energy release of the transformer 2 is completed and a voltage is generated in the tertiary winding 6 that forward biases the transistor 3, a differential current I _B1 based on this voltage flows into the transistor 3, and the transistor 3 rapidly and It will definitely turn on. Also, the collector current I _C is
When h _FE /I _B is reached and transistor 3 is turned off, the voltage on capacitor 38 is discharged through diode 40, a reverse bias voltage is applied to transistor 3, and transistor 3 is quickly turned off.
Note that the solid lines indicating I _C , I _B1 , I _B2 , and I _B in FIG. 8 indicate the state where the input voltage is maximum, and the dotted line indicates the state where the input voltage is minimum. In this embodiment, no current is supplied from the tertiary winding 6 during the entire on period of the transistor 3, so that efficiency can be improved.

Fifth Embodiment The converter according to the fifth embodiment shown in FIG.
The resistor 11 of the converter shown in FIG. 5 is replaced with a differentiating circuit consisting of a capacitor 38 and a resistor 39, and a diode 40 is added. Therefore, the operation of the circuit other than the capacitor 38 is the same as in FIG. 5, and the operation of the circuit related to the capacitor 38 is the same as in FIG.

Sixth Embodiment The sixth embodiment of the converter shown in FIG.
In place of the resistor 11 of the converter shown in the figure, the capacitor 38
A differential circuit consisting of a resistor 39 and a resistor 39 is provided. Note that a capacitor 41, a diode 42, and a resistor 43 are added in FIG. In this circuit as well, the operation is the same as that shown in FIG. 6 except for the differentiating circuit, and the operation of the differentiating circuit is the same as that shown in FIG. 7.

Seventh Embodiment The converter of the seventh embodiment shown in FIG. 11 is configured as a separately excited oscillation circuit. That is, except for the circuit that supplies the control signal to the base of the switching transistor 3, the configuration is the same as that shown in FIG. have. The control pulse supply circuit 44 generates a control pulse formed to perform constant voltage control based on the output voltage, and is coupled to the primary winding 46 of the transformer 45. A secondary winding 47 of the transformer 45 is connected to the base of the switching transistor 3 via a capacitor 38 and a resistor 39. Therefore, the switching transistor 3 is turned on in response to the pulse from the pulse supply circuit 44, and thereafter the feedback current from the current transformer 17 becomes the base current.

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

(A) A resistor 11 or a capacitor 38 may be connected to the lower side of the tertiary winding 6.

(B) The current transformer 17 may be connected to the emitter side of the transistor 3.

(C) In Figures 3, 5, and 6, a parallel circuit consisting of a varistor and a capacitor is connected to the tertiary winding 6.
may be connected in series.

(D) Light emitting diode 29 and phototransistor 3
0 may be replaced with a general transistor.

(E) The converters shown in Figures 5, 6 and 7 are connected to
As shown in FIG. 1, a separately excited system may be used.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram of a conventional DC-DC converter, Fig. 2 is a waveform diagram showing the states of each part in Fig. 1, and Fig. 3 is a circuit diagram of a converter according to the first embodiment of the present invention. , FIG. 4 is a waveform diagram showing the state of each part in FIG. 3,
5, 6, and 7 are circuit diagrams showing the converters of the second, third, and fourth embodiments, respectively; FIG. 8 is a waveform diagram showing the states of each part in FIG. 7; 9th
10 and 11 are circuit diagrams respectively showing fifth, sixth and seventh embodiments of the present invention. 1...DC power supply, 2...Transformer, 3...Switching transistor, 4...Primary winding, 5...Secondary winding,
6... Tertiary winding, 8... Rectifier smoothing circuit, 15... Constant voltage control circuit, 17... Current transformer, 18... Primary winding, 19
... Secondary winding, 20 ... Rectifier diode, 21 ... Overcurrent control transistor, 22 ... Overcurrent detection resistor,
23... Comparison 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 rectifier and smoothing circuit 8 connected to the secondary winding 5.
and a primary winding 18 of a current transformer 17 connected in series with the switching transistor 3, and a current corresponding to the current of the primary winding 18 of the current transformer 17 is connected to the base of the switching transistor 3. a secondary winding 19 of the current transformer 17 connected between the base and emitter of the switching transistor 3 so as to supply the current to the current transformer 17; The voltage drop across the overcurrent detection resistor 22, the overcurrent control transistor 21 connected between the base and emitter of the switching transistor 3, and the overcurrent detection resistor 22 exceeds a certain value. an overcurrent control current supply connected between one end of the overcurrent detection resistor 22 and the base of the overcurrent control transistor 21 so as to cause the overcurrent control transistor 21 to perform an overcurrent control operation in response to the overcurrent control transistor 21; A DC-DC converter comprising: a circuit; and a control signal supply circuit for supplying a control signal for controlling on/off of the switching transistor 3 to the base of the switching transistor 3. 2. The overcurrent control current supply circuit is a circuit including a semiconductor switch element that is turned on in response to a voltage drop across the overcurrent detection resistor 22 exceeding a certain value. DC-DC converter described in section. 3. The DC-DC converter according to claim 2, wherein the semiconductor switch element is a Zener diode 25. 4 The semiconductor switch element is a transistor 2
3. The DC-DC converter according to claim 2. 5. The control signal supply circuit is a circuit including a tertiary winding 6 electromagnetically coupled to the primary winding 4 of the transformer 2 and connected between the base and emitter of the switching transistor 3. The DC-DC converter according to the range 1, 2, 3, or 4. 6. The control signal supply circuit is a circuit that supplies pulses controlled by the output voltage obtained from the rectification and smoothing circuit 8.
The DC-DC converter according to item 1 or 3 or 4.