JPH0242078Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a transistor DC converter for use in a DC power supply circuit for video equipment, audio equipment, etc.

[Conventional technology]

As shown in FIG. 2, a series circuit consisting of a primary winding 3 of a transformer 2 and a switching transistor 4 is connected to a DC power supply 1, and a rectifier circuit consisting of a diode 6 and a capacitor 7 is connected to the secondary winding 5 of the transformer 2. The circuit is connected, and a tertiary winding 9 is provided in the transformer 2 for driving the base. This tertiary winding 9 is connected to the base of the transistor 4 via a resistor 10, and a constant voltage is applied to the base of the transistor 4. A switching regulator to which the control circuit 11 is connected to obtain a constant voltage at the output terminal 12 is well known. Note that 13 is a commercial AC power source, which is connected to the DC power source 1 consisting of a rectifier circuit. 14 is a starting resistor, and DC power supply 1
and the base of transistor 4. The voltage control circuit 11 includes a base current bypass transistor 15 connected between the base and emitter of the switching transistor 4, a diode 16, a capacitor 17, and a Zener diode 18 for controlling the transistor 15. The capacitor 17 is charged with the voltage of the tertiary winding 9 (equivalent to the output voltage) when it is off, and the transistor 15 is controlled based on a comparison between this voltage and the reference voltage of the Zener diode 18.

In the switching regulator described above, when the supply of DC power is started, a starting current flows through the starting resistor 14 and oscillation starts. When the transistor 4 is turned on, the voltage of the power supply 1 is applied to the primary winding 3, a corresponding voltage is generated in the tertiary winding 9, and the base current flows from this winding 9 to the transistor 4.
I _B is supplied. After that, when the collector current of the transistor 4 is saturated, it is turned off, and during this off period, the diode 6 is turned on, and the transformer 2
energy is released to the output side. The output voltage is controlled by allowing a portion of the current I ₁ of the tertiary winding 9 to bypass the transistor 15 . Since this type of operation is well known, its explanation will be omitted.

By the way, in this type of device, if the voltage E _IN of the power supply 1 increases, the voltage of the primary winding 3 and the tertiary winding 9 will increase.
The voltage and current of will also increase. Since the switching regulator of FIG. 2 has a voltage control circuit 11, all of the current _I1 in the tertiary winding 9 is transferred to the transistor 4.
The voltage control transistor 15 is bypassed. Since the bypass current I ₂ is unrelated to driving the transistor 4, it ends up being a power loss. . This problem becomes noticeable when the AC power supply voltage to which the equipment is connected changes from, for example, 100V to 220V. The power supply circuit is switched according to changes in the AC power supply voltage so that it can be used with either a 100V AC power source in Japan or a 220V AC power source in a foreign country. Although it is conceivable to construct the circuit as follows, the circuit configuration becomes complicated and the switching operation becomes troublesome, and there is also a risk that the switching operation may be forgotten. Such a problem occurs not only when the AC power supply voltage changes, but also in any case where the DC power supply voltage changes for some reason.

In order to solve the above-mentioned problems, a capacitor is provided which is charged with a substantially constant voltage induced in the tertiary winding 9 when the switching transistor 4 is off, and the base current of the switching transistor is controlled by the charge of this capacitor. The supply method was patented in the 1980s.
No. 45187 and Japanese Patent Application No. 60-221670. According to this method, efficiency can be significantly improved when the input voltage is high.

[Problem that the invention attempts to solve]

However, the above application does not disclose a circuit for quickly turning off the switching transistor 4. Therefore, an object of the present invention is to provide a transistor DC converter with high switching speed by utilizing the invention of the above-mentioned application.

[Means for solving problems]

To achieve the above object, the present invention will be explained with reference to the reference numerals in the drawings showing the embodiments. A secondary winding 5 electromagnetically coupled to the primary winding 3 and a switching transistor 4 connected to the secondary winding 5.
a rectifier circuit 8 including a diode 6 that is turned on when the transistor is turned off; and a rectifier circuit 8 that is electromagnetically coupled to the primary winding 3 and the secondary winding 5 and connected between the base and emitter of the switching transistor 4. 3
In a DC converter including a secondary winding 9 and a constant voltage control circuit connected to the base of the switching transistor 4, a voltage between one end of the tertiary winding 9 and the base of the switching transistor 4 is provided. a first capacitor 20 connected to one end of the tertiary winding 9 and the first a diode 19 connected between one end of the capacitor 20, a circuit that charges the first capacitor 20 with the voltage generated in the transformer when the switching transistor 4 is turned off, and an emitter of the It is connected to one end of a capacitor 20, its collector is connected to the emitter of the switching transistor 4, and its base is connected to one end of the tertiary winding 9 via a resistor 23, and when the switching transistor 4 is turned on, The present invention relates to a transistor DC converter characterized in that it includes an on-control transistor 22 having a polarity that turns on, and a second capacitor 24 connected in parallel to the resistor 23.

[Effect]

In the above invention, when a voltage is generated in the tertiary winding 9 in the direction of turning on the switching transistor 4, the voltage between the second capacitor 24, the base-emitter of the on-control transistor 22, the first capacitor 20, and the switch is connected. Current flows through the circuit consisting of the base and emitter of the switching transistor 4,
The two transistors 4, 22 turn on quickly. Conversely, when a voltage that turns off the switching transistor 4 is generated in the tertiary winding 9, the charging voltage of the second capacitor 24 increases between the tertiary winding 9 and the emitter-base of the switching transistor 4. , is applied to the circuit consisting of the first capacitor 20 and the emitter-base of the on-control transistor 22, and the two transistors 4 and 22 are reverse biased and quickly turned off.

〔Example〕

Next, a switching regulator according to an embodiment of the present invention will be described with reference to FIG. However, since the parts denoted by numerals 1 to 18 are substantially the same as those denoted by the same numerals in FIG. 2, the explanation thereof will be omitted. In this embodiment, a first capacitor 20 is connected between one end of the tertiary winding 9 and the base of the switching transistor 4 via a first diode 19 and a resistor 10. The first diode 19 is connected between one end of the tertiary winding 9 and one end (right end) of the first capacitor 20, and is turned on by the voltage induced in the tertiary winding 9 when the switching transistor 4 is off. It has the following polarity.

In order to configure a charging circuit for the first capacitor 20, a second diode 21 is connected between the other end (lower end) of the tertiary winding 9 and the other end (left end) of the first capacitor 20. There is. This second diode 21 has a polarity that turns on when the switching transistor 4 is off.

An npn transistor 22 is provided to form an on-control circuit by discharging the first capacitor 20. This ON control transistor 22
The emitter of is connected to one end (right end) of the first capacitor 20, and its base is connected to the tertiary winding 9 through a parallel circuit of a resistor 23 and a second capacitor 24.
The collector is connected to one end of the switching transistor 15 via a backflow blocking diode 25.
It is connected to the Emitsuta. The second capacitor 24 is related to the present invention, and is set to have a smaller capacitance than the first capacitor 20.

〔motion〕

In the circuit shown in Figure 1, turn on the power switch (not shown).
When turned on, the base current of the switching transistor 4 is supplied through the starting resistor 14, and the switching transistor 4 is turned on. After that, when the switching transistor 4 is saturated and turned off, the diode 6 is turned on, and the energy stored in the transformer 2 when the switching transistor 4 is on is released, and when this release is finished, the switching transistor is turned off again. 4 is turned on.

By the way, during the off period of the switching transistor 4, a substantially constant voltage is generated in the tertiary winding 9 regardless of the history of the power supply voltage _EIN . Since this voltage is opposite to the voltage when the switching transistor 4 is turned on, the second diode 21 is turned on, and the tertiary winding 9, the second diode 21, the first capacitor 20, and first diode 19
A closed circuit consisting of the first capacitor 2 is formed.
0 is charged with constant voltage. In this off state, the collector-emitter of the on-control transistor 22 is forward biased by the voltage of the tertiary winding 9.
Since the base is reverse biased, this ON control transistor 22 is kept in the OFF state.

When switching transistor 4 is on, 3
Based on the voltage of the next winding 9, the second capacitor 2
4, between the base and emitter of the on-control transistor 22, the first capacitor 20, and the resistor 10.
A current flows through the circuit consisting of the base and emitter of the switching transistor 4, and the two transistors 4 and 22 are quickly turned on. When the on-control transistor 22 is turned on, the first capacitor 20, the resistor 10, the base-emitter of the switching transistor 4, the backflow blocking diode 25, and the on-control transistor 2 are connected.
2 is formed, and the base current I _B of the switching transistor 4 is supplied based on the voltage of the first capacitor 20 which is charged almost constantly.

With this circuit, the AC power supply voltage can be changed from, for example, 100V.
When the voltage changes to 220V, the voltage of the tertiary winding 9 also increases when the switching transistor 4 is turned on, but
Since the capacitance C 2 of the second capacitor 24 is set lower than the capacitance C ₁ of the first capacitor 20, charging of the second capacitor ₂₄ is completed within a short time, and the base of the ON control transistor 22 is Only a limited base current flows through the resistor 23. The switching transistor 4 is therefore driven substantially independently of the high voltage of the tertiary winding 9, but dependent on the first capacitor 20;
An increase in the current bypassed by the constant voltage control transistor 15 can be suppressed.

The present invention is not limited to the above-described embodiments, but can be modified as follows, for example.

(a) Instead of the constant voltage control circuit 11 in FIG. 1, the voltage at the output terminal 12 is detected, an error signal between this detected voltage and the reference voltage is formed, and based on this error signal, a constant voltage control transistor is A circuit for controlling 15 may be provided.

(b) The charging circuit may be constructed by connecting a resistor instead of the diode 21.

[Effect of idea]

As is clear from the above, according to the present invention, the second
The switching transistor and the on-control transistor can be quickly turned on and off by the capacitor.

[Brief explanation of the drawing]

FIG. 1 is a circuit diagram showing a switching regulator according to an embodiment of the present invention, and FIG. 2 is a circuit diagram showing a conventional switching regulator. 1...Power supply, 2...Transformer, 3...Primary winding, 4...Switching transistor, 5...2
Secondary winding, 8... Rectifier circuit, 9... Tertiary winding, 19
...first diode, 20...first capacitor, 21...second diode, 22...on control transistor, 24...second capacitor.

Claims (1)

[Claims for Utility Model Registration] A series circuit of a transformer primary winding 3 connected to a DC power supply 1 and a switching transistor 4, a secondary winding 5 electromagnetically coupled to the primary winding 3, A rectifier circuit 8 is connected to the secondary winding 5 and includes a diode 6 that is turned on when the switching transistor 4 is turned off, and is electromagnetically coupled to the primary winding 3 and the secondary winding 5 and In the DC converter, the DC converter includes a tertiary winding 9 connected between the base and emitter of the switching transistor 4, and a constant voltage control circuit connected to the base of the switching transistor 4, A first capacitor 20 connected between one end of the secondary winding 9 and the base of the switching transistor 4 is turned on by a voltage induced in the tertiary winding 9 when the switching transistor 4 is turned off. a diode 1 connected between one end of the tertiary winding 9 and one end of the first capacitor 20 with polarity;
9; a circuit for charging the first capacitor 20 with a voltage generated in the transformer when the switching transistor 4 is turned off; an emitter thereof is connected to one end of the first capacitor 20, and a collector thereof is connected to the switch an on-control transistor connected to the emitter of the switching transistor 4, whose base is connected to one end of the tertiary winding 9 via a resistor 23, and has a polarity that turns on when the switching transistor 4 is on; 22; and a second capacitor 24 connected in parallel to the resistor 23.