JP2003047243A - Switching power supply apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a switching power supply apparatus which can simplify a structure of a voltage control circuit controlling a switching device and, further, can employ a transformer having three terminals on its primary side. SOLUTION: In a switching power supply apparatus which controls a switching device provided on a primary side of a transforming means and applies a voltage to the primary winding of the transforming means to induce a voltage in its secondary winding, a voltage control circuit is composed of one transistor device. A drive winding which detects the voltage induced in the secondary winding is provided on the primary side and a terminal of one of the primary winding and the drive winding is used in common with a center tap.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is one of transformer means.
The present invention relates to a switching power supply device that induces a voltage in a secondary winding by controlling a switching element provided on the secondary side and applying a voltage to the primary winding.

[0002]

2. Description of the Related Art FIG. 5 is a diagram showing a configuration example of a conventional switching power supply device. In this figure, ringing
An example of a choke converter is shown. In FIG. 5, the voltage source 10 generates a DC voltage. The negative side of the voltage source 10 is connected to the common potential point. The transformer means 11 has a structure in which the primary winding 12 and the drive winding 13 are provided on the primary side and the secondary winding 14 is provided on the secondary side. The switching element 15 is composed of an NPN type transistor.
The voltage source 10, the primary winding 12 and the switching element 15 are connected in series, and the DC voltage of the voltage source 10 is applied to the primary winding 12 via the switching element 15. A voltage is induced in the secondary winding 14 by controlling the switching element 15 and applying a voltage to the primary winding 12.

An AC voltage generated in the secondary winding 14 is converted into a DC output voltage V0 by a rectifying / smoothing circuit including a diode 16 and a capacitor 17. The diode 18 and the capacitor 19 are connected in series at both ends of the drive winding 13. The voltage generated across the drive winding 13 is the diode 1
It is rectified and smoothed by 8 and the capacitor 19.

The resistor 20 is connected between one end of the drive winding 13 and the base of the switching element 15. Resistance 2
1 is connected between one end of the primary winding 12 and the base of the switching element 15. The winding directions of the primary and secondary windings are opposite. The transistor 22 is composed of an NPN type transistor, and the emitter is the capacitor 1
9, the collectors are connected to the bases of the switching elements 15, respectively. The voltage control circuit 23 receives the potential V1 at the connection point between the diode 18 and the capacitor 19,
The driving of the transistor 22 is controlled so that the potential V1 becomes constant.

In the circuit of FIG. 5, the output voltage on the secondary side is V0,
The forward voltage drop of each of the diodes 18 and 16 is determined by VF.
1, VF2, the number of turns of the drive winding 13 and the number of turns of the secondary winding 14 are N2 and N3, respectively, the following equation holds because the output voltage of the transformer is proportional to the winding ratio. -(V0 + VF2) / (V1 + VF1) = N3 / N2 The voltage control circuit 23 is composed of an operational amplifier and has a voltage V1.
Is controlled to be constant. This allows N3 and N
It is possible to obtain an output voltage according to the winding ratio of 2. In the operational amplifier that constitutes the voltage control circuit 23, the negative side input terminal is the connection point of the diode 18 and the capacitor 19 (potential V
1), the positive side input terminal is connected to the common potential point, and the output terminal is connected to the base of the transistor 22. For example, if N2 = N3 is set for simplicity and the forward voltage drops VF1 and VF2 are equal, -V0 = V
It becomes 1.

However, in the conventional example of FIG. 5, since the operational amplifier is used in the voltage control circuit, there is a problem that the circuit configuration becomes complicated. Further, since the primary winding and the drive winding are provided with two terminals each, there is a problem that a transformer having three terminals on the primary side cannot be used.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and can simplify the configuration of the voltage control circuit, and can use a transformer having three terminals on the primary side. It is intended to realize a switching power supply device.

[0008]

The present invention is a switching power supply device having the following configuration.

(1) A voltage generated in the secondary winding by inducing a voltage in the secondary winding by controlling a switching element provided on the primary side of the transformer means and applying a voltage to the primary winding. Is detected by the drive winding provided on the primary side, the voltage control circuit controls the switching element based on the detected voltage, and the output voltage on the secondary side is controlled to be constant. The control circuit is composed of a first transistor element whose collector current changes according to the detection voltage of the drive winding, the collector current flowing by driving the first transistor element is supplied to the base, and the base current causes the collector voltage to flow. Changes, and the switching power supply device has a second transistor element for controlling the time for which the switching element is turned on by the voltage across this voltage.

(2) The switching power supply device according to (1), characterized in that the voltage control circuit has a configuration in which a voltage dividing circuit is provided in a stage preceding the base of the first transistor element.

(3) In the voltage control circuit, an emitter follower including a transistor element and a resistor is provided in front of the base of the first transistor element, and a voltage dividing circuit is connected to the base of the transistor element in the emitter follower. The switching power supply device according to (1) is characterized in that a voltage according to the detection voltage of the drive winding is applied to the voltage dividing circuit.

(4) In the voltage control circuit, a voltage dividing circuit is provided in front of the base of the first transistor element,
An emitter follower including a transistor element and a resistor is connected to the emitter of the transistor element, and the transistor element in the emitter follower and the emitter of the first transistor element are commonly connected to the resistor in the emitter follower, and the voltage divider circuit is connected to the resistor. The switching power supply device according to (1), wherein the switching power supply device is configured to apply a voltage according to the detection voltage of the drive winding.

(5) One of the terminals of the primary winding and the drive winding shares a center tap, one end of the primary winding is connected to a common potential point, and the switching element has a voltage on the primary side. The switching power supply device according to (1), which is connected to the positive side of the power source.

[0014]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in detail below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of the present invention. In FIG. 1, the same parts as those in the previous figure are designated by the same reference numerals.
The switching power supply device of the embodiment is a ringing choke converter. In FIG. 1, the transformer means 31 is
The primary winding 32 and the drive winding 33 are provided on the secondary side, and the secondary winding 34 is provided on the secondary side. Primary winding 3
2 and one terminal of the drive winding 33 share the center tap 35. The winding directions of the primary and secondary windings are opposite. One end (the terminal on the side of the center tap 35) of the primary winding 32 is connected to the common potential point.

The diode 36 and the capacitor 37 are connected in series at both ends of the drive winding 33. The voltage generated across the drive winding 33 is rectified and smoothed by the diode 36 and the capacitor 37. The switching element 38 is M
It is composed of an OS type FET. The source of the switching element 38 is connected to the positive side of the voltage source 10, and the drain is connected to one end of the primary winding 32. The resistor 39 is
One end is connected to the gate of the switching element 38, and the other end is connected to the common potential point. The capacitor 40 is
One end is connected to the gate of the switching element 38, and the other end is connected to one end of the drive winding 33.

The transistor element 41 is composed of a PNP type transistor. Transistor element 41
Has an emitter connected to the positive side of the voltage source 10 and a collector connected to the gate of the switching element 38. The voltage control circuit 42 is composed of one transistor element 421. The transistor element 421 is composed of an NPN type transistor, and has a control voltage Vct at its emitter.
rl is applied, the collector is connected to the base of the transistor element 41, and the base is connected to the cathode side of the diode 36. The control voltage Vctrl is a constant voltage supplied from a constant voltage source or the like.

In the circuit of FIG. 1, the output voltage of the rectifying and smoothing circuit composed of the diode 36 and the capacitor 37 is V10,
The forward voltage drop of each of the diodes 36 and 16 is calculated as VF.
Assuming that the numbers of turns of 10, VF20, drive winding 33 and secondary winding 34 are N2 and N3, respectively, the output voltage of the transformer is proportional to the winding ratio, and therefore the following equation is established. (V0 + VF20) / (V10 + VF10) = N3 / N
Two

The transistor element 421 controls the output voltage V0 as follows. The base-emitter voltage of the transistor element 421 is VBE3. V10> Vct
When rl + VBE3 is reached, the transistor element 421 is turned on, a base current flows through the transistor element 41, and the gate-source voltage of the switching element 38 is reduced. As a result, the time during which the switching element 38 is on is shortened and the rise of the output voltage V0 is suppressed. This stabilizes the voltage so that V10 = Vctrl + VBE3. At this time, the output voltage V0 is given by the following equation. V0 = (N3 / N2) ・ (Vctrl + VBE3 + VF1
0) -VF20

FIG. 2 is a block diagram showing another embodiment of the present invention. The circuit of FIG. 2 is a circuit in which the voltage control circuit 42 is provided with a voltage dividing circuit including resistors 422 and 423 to increase the degree of freedom of the output voltage V0. In the circuit of FIG. 2, the output voltage V10 of the rectifying / smoothing circuit including the diode 36 and the capacitor 37 is divided by the resistors 422 and 423 and input to the base of the transistor element 421. In this circuit, the output voltage V10 is given by the following equation. V0 = (N3 / N2) * {A (Vctrl + VBE3) + V
F10} -VF20 A = (R2 + R3) / R3 R2: resistance value of resistor 422, R3: resistance value of resistor 423 For the sake of simplicity, if N3 = N2 and VF10 = VF20 are set, V0 = {(R2 + R3) / R3 } ・ (Vctrl + VBE
3)

FIG. 3 is a block diagram showing another embodiment of the present invention. The base-emitter voltage of a transistor changes under the influence of ambient temperature. That is, the base-emitter voltage becomes an error factor of the output voltage. The embodiment of FIG. 3 solves this problem. In the embodiment of FIG. 3, an emitter follower including a transistor element 424 and a resistor 425 is added to the voltage control circuit of the embodiment of FIG. The transistor element 424 is a PNP type transistor, the emitter is the base of the transistor element 421, the collector is the common potential point, and the bases are the resistors 422 and 423.
Are connected to the respective connection points. The resistor 425 has one end on the positive side of the voltage source 10 and the other end on the transistor element 42.
4 emitters, respectively. Assuming that the base-emitter voltages of the transistor elements 421 and 424 are equal, the base-emitter voltages of these two transistor elements cancel each other out. Therefore, the output voltage V0 is given by the following equation. V0 = {(R2 + R3) / R3} .Vctrl By this, the error factor of the base-emitter voltage can be removed.

FIG. 4 is a block diagram showing another embodiment of the present invention. The circuit of FIG. 4 is another configuration example for removing the influence of the base-emitter voltage of the transistor. In the voltage control circuit of this embodiment, an emitter follower including a transistor element 424 and a resistor 425 is added between the emitter of the transistor element 421 and the point where the control voltage Vctrl is applied. The emitter of the transistor element 424 and the emitter of the transistor element 421 are commonly connected to the resistor 425.
Is connected to one end of. The collector of the transistor element 424 is connected to the positive side of the voltage source 10, and the control voltage Vctrl is applied to the base. The other end of the resistor 425 is connected to the common potential point.

Also in the voltage control circuit of this embodiment, if the base-emitter voltages of the transistor elements 421 and 424 are equal, the base-emitter voltages of these two transistor elements cancel each other out. Therefore, the output voltage V0
Is given by V0 = {(R2 + R3) / R3} · Vctrl

[0023]

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

According to the first aspect of the invention, since the voltage control circuit is composed of one transistor element, the structure of the voltage control circuit can be simplified as compared with the conventional example.

According to the second aspect of the invention, since the voltage control circuit is provided with the voltage dividing circuit, the degree of freedom of the output voltage of the switching power supply device can be increased.

In the third and fourth aspects of the invention, since the voltage control circuit is provided with the emitter follower, the error factor due to the base-emitter voltage of the transistor can be eliminated.

In the invention of claim 5, one terminal of the primary winding and the drive winding shares a center tap, one end of the primary winding is connected to a common potential point, and the switching element is on the primary side. It is connected to the positive side of the voltage source. With such a configuration, a transformer having three terminals on the primary side can be used.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment of the present invention.

FIG. 2 is a configuration diagram showing another embodiment of the present invention.

FIG. 3 is a configuration diagram showing another embodiment of the present invention.

FIG. 4 is a configuration diagram showing another embodiment of the present invention.

FIG. 5 is a diagram showing a configuration example of a conventional switching power supply device.

[Explanation of symbols]

10 voltage source 31 Transformer Means 32 primary winding 33 Drive winding 34 Secondary winding 35 Center tap 38 switching elements 41 Transistor element (second transistor element) 42 Voltage control circuit 421 transistor element (first transistor element) 422, 423, 425 resistance 424 Transistor element

Claims (5)

[Claims] 1. A switching element provided on the primary side of the transformer means is controlled to apply a voltage to the primary winding, thereby inducing a voltage in the secondary winding and reducing the voltage generated in the secondary winding. The voltage is detected by the drive winding provided on the primary side, and the voltage control circuit controls the switching element based on the detected voltage.
In the switching power supply device for controlling the output voltage on the secondary side to be constant, the voltage control circuit includes a first transistor element whose collector current changes according to the detection voltage of the drive winding. A switching power supply having a second transistor element for controlling a time when the switching element is turned on by the collector current flowing by the driving of the apparatus. 2. The switching power supply device according to claim 1, wherein the voltage control circuit is configured such that a voltage dividing circuit is provided in a stage preceding the base of the first transistor element. 3. The voltage control circuit includes an emitter follower formed of a transistor element and a resistor in front of the base of the first transistor element, and the voltage divider circuit is connected to the base of the transistor element in the emitter follower.
2. The switching power supply device according to claim 1, wherein a voltage according to the detection voltage of the drive winding is applied to the voltage dividing circuit. 4. The voltage control circuit is provided with a voltage dividing circuit in a stage preceding the base of the first transistor element, and an emitter follower including a transistor element and a resistor is connected to the emitter of the first transistor element, The transistor element in the follower and the emitter of the first transistor element are commonly connected to a resistor in the emitter follower, and a voltage according to the detection voltage of the drive winding is applied to the voltage dividing circuit. The switching power supply device according to claim 1. 5. One of the terminals of the primary winding and the drive winding shares a center tap, one end of the primary winding is connected to a common potential point, and the switching element is a voltage source on the primary side. 2. It is connected to the positive side of
The switching power supply described.