JPH0250715B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transistor DC converter for use in DC power supply circuits of 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, and this tertiary winding 9 is connected to the base of the transistor 4 via a resistor 10, and furthermore, a voltage control is applied to the base of the transistor 4. Connect circuit 11,
A switching regulator that obtains a constant voltage at the output terminal 12 is well known. Note that 14 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, which is connected between the DC power supply 1 and the base of the 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 when it is off (equivalent to the output power supply), 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, the present applicant proposed in Japanese Patent Laid-Open No. 60-45187 a capacitor that is charged with a substantially constant voltage induced in the tertiary winding 9 when the switching transistor 4 is turned off. We proposed a method in which the base current of the switching transistor is supplied by the charge of this capacitor. According to this method, efficiency can be significantly improved when the human power voltage is high.

[Problem that the invention seeks to solve]

However, the circuit shown as an example in the above application is constructed in such a way that the switch element for forming the discharge circuit of the capacitor is forward biased with the tertiary winding. Therefore, a relatively large current flows through the discharge circuit forming switch element based on the voltage of the tertiary winding.

Therefore, an object of the present invention is to provide an extremely efficient transistor DC converter by utilizing the invention of the above application.

[Means for solving problems]

To achieve the above object, the present invention will be described 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 having a secondary winding 9, a switching transistor driving capacitor 20 connected between the tertiary winding 9 and the switching transistor 4, and a switching transistor driving capacitor 20 connected between the tertiary winding 9 and the switching transistor 4, a first diode 19 connected between one end of the tertiary winding 9 and one end of the capacitor 20 and having a polarity turned on by a voltage induced in the tertiary winding 9; A second capacitor connected between the other end of the tertiary winding 9 and the other end of the capacitor 20 and having a polarity that is turned on by a voltage induced in the tertiary winding 9 when the switching transistor 4 is turned off. the diode 21 and the capacitor 2
0 and the emitter of the switching transistor 4, and has a direction such that a forward voltage is applied between the emitter and the collector by the voltage of the capacitor 20 when the switching transistor 4 is turned on. When the switching transistor 4 is off, no on-drive base current is supplied to the control transistor 22, and when the switching transistor 4 is on, the discharge control transistor 22 is
The present invention relates to a transistor DC converter characterized by comprising a base control circuit that supplies an on-drive base current to the transistor.

[Effect]

Since the above invention utilizes the invention of the earlier application, the basic operation is the same as that of the earlier application. However, the discharge control transistor 22
Since it is connected in a forward direction relative to the tertiary winding 9 and in a reverse direction relative to the tertiary winding 9, the collector current of the discharge control transistor 22 is not supplied from the tertiary winding when the switching transistor is turned on.
Therefore, almost no current flows through the tertiary winding 9 when turned on, and power loss is significantly reduced.

〔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 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 capacitor 20, and has a polarity that is turned on by the voltage induced in the tertiary winding 9 when the switching transistor 4 is off. have.

In order to configure the charging circuit for the 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 capacitor 20. This second diode 21 has a polarity that turns on when the switching transistor 4 is off.

A discharge control transistor 22 for forming a discharge circuit for the capacitor 20 is connected between one end (right end) of the capacitor 20 and the emitter of the switching transistor 4, and is connected to the tertiary winding 9 when the switching transistor 4 is off. It has a polarity that is reverse biased at a voltage of . This discharge control transistor 2
The base of the transistor 2 is connected to one end of the tertiary winding 9 via a resistor 23 in order to turn on the transistor 2 only when the switching transistor 4 is on.

Incidentally, a capacitor 24 connected between one end of the tertiary winding 9 and the base of the switching transistor 4 is used to quickly start the operation.

〔motion〕

In the circuit of FIG. 1, when a power switch (not shown) is 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 turned on is released, and the switching transistor 4 is turned on again. . In addition to the above-described oscillation operation, a constant voltage output is obtained at the output terminal 12 by constant voltage control by the voltage control circuit 11.

By the way, during the off period of the switching transistor 4, a substantially constant voltage is generated in the tertiary winding 9, which is unrelated to 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 capacitor 20, and the first A closed circuit consisting of the diode 19 is formed, and the capacitor 20 is charged at a constant voltage. In this off state, the voltage in the tertiary winding 9 is generated in a direction that forward biases the discharge control transistor 22, but the base of the discharge control transistor 22 is connected to the upper end of the tertiary winding 9 via the resistor 23. Therefore, no base current flows and the discharge control transistor 22 is kept in an off state.

When the switching transistor 4 is turned on after the capacitor 20 is charged, the capacitor 20,
Through a closed circuit consisting of a resistor 10, a switching transistor 4, and a discharge control transistor 22,
The discharge current of the capacitor 20 flows, and the base current of the switching transistor 4 is supplied. At this time, the voltage of the tertiary winding 9 is in the direction of reverse biasing between the emitter and collector of the discharge control transistor 22, and since the first diode 19 is provided, the discharge is performed using the tertiary winding 9 as a power source. The collector current of control transistor 22 does not flow. However, the base current of the discharge control transistor 22 is supplied from the tertiary winding 9 via the resistor 23, and the discharge control transistor 22 is controlled to be turned on. As a result, a discharge circuit for the capacitor 20 is established, and a base current is supplied to the switching transistor 4.

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 first diode 19 is turned off, the voltage on the tertiary winding 9 becomes substantially independent of the driving of the switching transistor 4 and the charging of the capacitor 20. Therefore, the switching transistor 4 is controlled in the same way as when the AC power supply voltage is 100V, and a constant voltage is obtained at the output terminal 12 regardless of fluctuations in the input voltage.

As is clear from the above, in the circuit shown in FIG. 1, the constant voltage control transistor 15 does not absorb fluctuations in the input voltage, so power loss is reduced. Furthermore, the dynamic range of the constant voltage control transistor 15 may be narrow. Further, when the output terminal 12 is short-circuited, the voltage of the capacitor 20 decreases, so that the on period of the switching transistor 4 is shortened, and a fold-back droop characteristic is obtained. Furthermore, when the switching transistor 4 is on, the tertiary winding 9 supplies the base current of the discharge control transistor 22, and
Since the starting current is only supplied through the capacitor 24 and the collector current of the discharge control transistor 22 is not supplied, power loss is significantly reduced, and efficiency is greatly improved, especially when the input voltage is high.

The present invention is not limited to the embodiments described above, but may be modified. For example, as shown in FIG. 3, in order to control the constant voltage control transistor 15, the voltage at the output terminal 12 may be detected and a control signal for keeping this voltage constant may be generated by the constant voltage control circuit 27. good. Alternatively, the constant voltage control transistor 15 may be omitted from the circuit shown in FIG. 1, and the cathode of the Zener diode 18 may be connected to the base of the switching transistor 4. Further, it is also applicable to a case where the constant voltage control circuit 11 is not provided.
Alternatively, as shown in FIG. 3, a quaternary winding 26 may be provided in the transformer 2, and the base current of the discharge control transistor 22 may be supplied by the voltage of the quaternary winding 26 when the switching transistor 4 is on. good. Further, a speed-up capacitor may be connected in parallel to the resistors 10 and 23. Further, the capacitor 20 may be connected in series to the lower end line of the tertiary winding 9. Furthermore, instead of flowing the starting current through the starting resistor 14, a starting pulse may be supplied.

〔Effect of the invention〕

As is clear from the above, according to the present invention, a simple circuit configuration consisting of a capacitor and this charge/discharge control circuit can prevent fluctuations in the output voltage corresponding to fluctuations in the input power supply voltage. Also,
Decrease in efficiency when the input power supply voltage is high can be suppressed.

[Brief explanation of drawings]

Fig. 1 is a circuit diagram showing a switching regulator according to an embodiment of the present invention, Fig. 2 is a circuit diagram showing a conventional switching regulator, and Fig. 3 is a circuit diagram showing a switching regulator according to a modified example. It is a circuit diagram showing a part. 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...Capacitor, 2
1...Second diode, 22...Discharge control transistor.

Claims (1)

[Claims] 1. Transformer primary winding 3 connected to DC power supply 1
and a series circuit with a switching transistor 4,
a secondary winding 5 electromagnetically coupled to the primary winding 3;
a diode 6 connected to the secondary winding 5 and turned on when the switching transistor 4 is turned off;
and a tertiary winding 9 electromagnetically coupled to the primary winding 3 and the secondary winding 5 and connected between the base and emitter of the switching transistor 4. The DC converter includes: a switching transistor driving capacitor 20 connected between the tertiary winding 9 and the switching transistor 4; and a switching transistor driving capacitor 20 connected between the tertiary winding 9 and the switching transistor 4; One end of the tertiary winding 9 and the capacitor 2
A first diode 1 connected between one end of 0
9, and has a polarity that is turned on by a voltage induced in the tertiary winding 19 when the switching transistor 4 is turned off, and is connected between the other end of the tertiary winding 9 and the other end of the capacitor 20. a second diode 21 connected between one end of the capacitor 20 and the emitter of the switching transistor 4; a discharge control transistor 22 having a direction in which a forward voltage is applied to the discharge control transistor 22; no on-drive base current is supplied to the control transistor 22 when the switching transistor 4 is off; A transistor DC converter comprising: a base control circuit that supplies an on-drive base current to the discharge control transistor 22.